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an important notice at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications, intellectual property matters and other important disclaimers. unless otherwise noted, this document contains production data. ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 ads126x precision, 5-channel and 10-channel, 40-ksps, 24-bit, delta-sigma adcs with pga and monitors 1 1 features 1 ? 24-bit, high-precision adcs ? offset drift: 1 nv/ c ? gain drift: 0.5 ppm/ c ? noise: 30 nv rms (20 sps, gain = 128) ? linearity: 2 ppm ? cmos pga gain: 1 to 128 ? wide input voltage range: 7 mv to 5 v ? data rate: 2.5 sps to 40 ksps ? simultaneous 50-hz and 60-hz rejection mode ? single-cycle settling mode ? signal and reference monitors ? 5-v or 2.5-v power supply ? internal temperature sensor ? cyclic redundancy check ? excitation current sources ? sensor burn-out current sources ? four general-purpose input/outputs (ads1261) ? ac excitation for bridge sensors (ads1261) ? 5-mm 5-mm qfn package 2 applications ? plc analog input modules ? weigh scales and strain-gauge digitizers ? temperature, pressure measurement ? lab instrumentation ? process analytics 3 description the ads1260 and ads1261 (ads126x) are precision, 40-ksps, delta-sigma ( ) analog-to-digital converters (adcs) with an integrated programmable gain amplifier (pga) and internal fault monitors. the sensor-ready adcs provide a high-accuracy, single- chip solution for the most demanding measurements, including weigh scales and resistance temperature devices (rtd). the adcs are comprised of an input signal multiplexer, a low-noise pga, providing gain from 1 to 128, a 24-bit modulator, and a programmable digital filter. the high-impedance pga inputs (1 g ) reduce measurement error caused by sensor loading. the ads1260 supports three differential or five single- ended inputs. the ads1261 supports five differential or 10 single-ended inputs. the integrated current sources simplify the measurement of rtds. the flexible digital filter is programmable for single- cycle settled conversions, while providing simultaneous 50-hz and 60-hz line cycle rejection. signal and reference monitors, a temperature sensor, and crc data verification enhance data reliability. the ads126x are pin compatible devices offered in a 5-mm 5-mm qfn package and are specified over the ? 40 c to +125 c temperature range. device information (1) part number package body size (nom) ads1260 (2) vqfn (32) 5.0 mm 5.0 mm ads1261 (1) for all available packages, see the package option addendum at the end of the data sheet. (2) the ads1260 device is preview. block diagram productfolder 24-bit ? adc pga input mux digital filter serial interface and crc verification cs dout/drdy sclk start clock mux clkin refout ref monitor signal monitor buf ain0 ain1 ain2 aincom supply monitor level shift temp sensor ads1260 ads1261 3 v 5 v (d) ref mux 2.5-v ref ain3 ain4 ain5 ain6 ain7 ain8 sensor excitation internal oscillator pwdn din 5 v (a) sensor test gpio ac-exc ads1261 reset ain9 (a) (d) control drdy support &community tools & software technical documents ordernow
2 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated table of contents 1 features .................................................................. 1 2 applications ........................................................... 1 3 description ............................................................. 1 4 revision history ..................................................... 2 5 device comparison table ..................................... 3 6 pin configuration and functions ......................... 3 7 specifications ......................................................... 5 7.1 absolute maximum ratings ...................................... 5 7.2 esd ratings .............................................................. 5 7.3 recommended operating conditions ....................... 6 7.4 thermal information .................................................. 6 7.5 electrical characteristics ........................................... 7 7.6 timing requirements .............................................. 10 7.7 switching characteristics ........................................ 11 7.8 typical characteristics ............................................ 14 8 parameter measurement information ................ 20 8.1 noise performance ................................................. 20 9 detailed description ............................................ 24 9.1 overview ................................................................. 24 9.2 functional block diagram ....................................... 25 9.3 feature description ................................................. 26 9.4 device functional modes ........................................ 41 9.5 programming ........................................................... 48 9.6 register map ........................................................... 57 10 application and implementation ........................ 70 10.1 application information .......................................... 70 10.2 typical application ................................................ 74 10.3 initialization setup ................................................. 77 11 power supply recommendations ..................... 78 11.1 power-supply decoupling ..................................... 78 11.2 analog power-supply clamp ................................ 78 11.3 power-supply sequencing .................................... 78 12 layout ................................................................... 79 12.1 layout guidelines ................................................. 79 12.2 layout example .................................................... 79 13 device and documentation support ................. 81 13.1 documentation support ........................................ 81 13.2 related links ........................................................ 81 13.3 receiving notification of documentation updates 81 13.4 community resources .......................................... 81 13.5 trademarks ........................................................... 81 13.6 electrostatic discharge caution ............................ 81 13.7 glossary ................................................................ 81 14 mechanical, packaging, and orderable information ........................................................... 81 4 revision history changes from original (march 2018) to revision a page ? changed ads1261 device from advanced information to production data (active) ............................................................... 1
3 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated (1) reference inputs, gpios, and ac excitation output drive are multiplexed with the analog inputs. (2) the ads1260 device is preview. 5 device comparison table part number channels reference inputs (1) gpio (1) ac-excitation (1) single-ended differential ads1260 (2) 5 3 1 ? ? ads1261 10 5 2 4 2 or 4 output drive 6 pin configuration and functions rhb package: ads1261 vqfn-32 top view 32 ain0 9 start 1 aincom 24 ain8 31 ain1 10 cs 2 capp 23 ain9 30 ain2 11 sclk 3 capn 22 nc 29 ain3 12 din 4 avdd 21 nc 28 ain4 13 drdy 5 avss 20 nc 27 ain5 14 dout/drdy 6 refout 19 nc 26 ain6 15 bypass 7 pwdn 18 clkin 25 ain7 16 dgnd 8 reset 17 dvdd not to scale thermal pad
4 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated pin functions pin type description no. name 1 aincom analog input/output analog input common, idac1, idac2, vbias 2 capp analog output pga output p; connect a 4.7-nf c0g dielectric capacitor across capp and capn 3 capn analog output pga output n; connect a 4.7-nf c0g dielectric capacitor across capp and capn 4 avdd analog positive analog power supply 5 avss analog negative analog power supply 6 refout analog output internal 2.5-v reference output; connect a 10- f capacitor to avss 7 pwdn digital input power down, active low 8 reset digital input reset, active low 9 start digital input start conversion control, active high 10 cs digital input serial interface chip select, active low 11 sclk digital input serial interface shift clock 12 din digital input serial interface data input 13 drdy digital output data ready indicator, active low 14 dout/ drdy digital output dual function serial interface data output and active-low data ready indicator 15 bypass analog output internal subregulator bypass; connect a 1- f capacitor to dgnd 16 dgnd digital digital ground 17 dvdd digital digital power supply 18 clkin digital input 1) internal oscillator: connect to dgnd 2) external clock: connect clock input 19-22 nc ? no connection 23 ain9 analog input/output ads1260: no connection ads1261: analog input 9, idac1, idac2 24 ain8 analog input/output ads1260: no connection ads1261: analog input 8, idac1, idac2 25 ain7 analog input/output ads1260: no connection ads1261: analog input 7, idac1, idac2 26 ain6 analog input/output ads1260: no connection ads1261: analog input 6, idac1, idac2 27 ain5 analog input/output ads1260: no connection ads1261: analog input 5, idac1, idac2, gpio3, acx2 28 ain4 analog input/output ads1260: analog input 4, idac1, idac2 ads1261: analog input 4, idac1, idac2, gpio2, acx1 29 ain3 analog input/output ads1260: analog input 3, idac1, idac2 ads1261: analog input 3, idac1, idac2, refn1, gpio1, acx2 30 ain2 analog input/output ads1260: analog input 2, idac1, idac2 ads1261: analog input 2, idac1, idac2, refp1, gpio0, acx1 31 ain1 analog input/output analog input 1, idac1, idac2, refn0 32 ain0 analog input/output analog input 0, idac1, idac2, refp0 thermal pad thermal pad ? exposed thermal pad; connect to avss. pad must be soldered for mechanical integrity.
5 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated (1) stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. these are stress ratings only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under recommended operating conditions . exposure to absolute-maximum-rated conditions for extended periods may affect device reliability. (2) input and output pins are diode-clamped to the internal power supplies. limit the input current to 10 ma in the event the analog input voltage exceeds avdd + 0.3 v or avss ? 0.3 v, or if the digital input voltage exceeds dvdd + 0.3 v or dgnd ? 0.3 v. 7 specifications 7.1 absolute maximum ratings (1) min max unit power supply voltage avdd to avss ? 0.3 7 v avss to dgnd ? 3 0.3 dvdd to dgnd ? 0.3 7 analog input voltage ainx avss ? 0.3 avdd + 0.3 v digital input voltage cs, sclk, din, dout/ drdy, drdy, start, reset, pwdn, clkin dgnd ? 0.3 dvdd + 0.3 v input current continuous, all pins except power-supply pins (2) ? 10 10 ma temperature junction, t j 150 c storage, t stg ? 60 150 c (1) jedec document jep155 states that 500-v hbm allows safe manufacturing with a standard esd control process. (2) jedec document jep157 states that 250-v cdm allows safe manufacturing with a standard esd control process. 7.2 esd ratings value unit v (esd) electrostatic discharge human-body model (hbm), per ansi/esda/jedec js-001 (1) 2000 v charged-device model (cdm), per jedec specification jesd22-c101 (2) 500
6 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated (1) in pga mode, the maximum differential input voltage is (avdd - avss - 0.6 v) / gain, when operating with v ref avdd - avss - 0.6 v 7.3 recommended operating conditions min nom max unit power supply analog power supply avdd to avss 4.75 5 5.25 v avss to dgnd ? 2.6 0 digital power supply dvdd to dgnd 2.7 5.25 v analog inputs v (ainx) absolute input voltage pga mode see equation 5 v pga bypassed avss ? 0.1 avdd + 0.1 v in differential input voltage v in = v ainp ? v ainn v ref / gain see (1) v voltage reference inputs v ref differential reference voltage v ref = v (refpx) ? v (refnx) 0.9 avdd ? avss v v (refnx) negative reference voltage avss ? 0.05 v (refpx) ? 0.9 v v (refpx) positive reference voltage v (refnx) + 0.9 avdd + 0.05 v external clock f clk frequency 2.5 sps to 25.6 ksps 1 7.3728 8 mhz 40 ksps 1 10.24 10.75 duty cycle 40% 60% general-purpose inputs/outputs (gpios) input voltage avss avdd v digital inputs (other than gpios) input voltage dgnd dvdd v temperature t a operating ambient temperature ? 45 125 c (1) for more information about traditional and new thermal metrics, see the semiconductor and ic package thermal metrics application report. 7.4 thermal information thermal metric (1) ads1260, ads1261 unit vqfn (rhb) 32 pins r ja junction-to-ambient thermal resistance 28.6 c/w r jc(top) junction-to-case (top) thermal resistance 17.0 c/w r jb junction-to-board thermal resistance 9.7 c/w jt junction-to-top characterization parameter 0.2 c/w jb junction-to-board characterization parameter 9.7 c/w r jc(bot) junction-to-case (bottom) thermal resistance 0.7 c/w
7 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated (1) chop-mode input current scales with data rate. (2) normal-mode rejection ratio performance depends on the digital filter configuration. (3) common-mode rejection ratio is specified at f in = 60 hz. (4) power-supply rejection ratio specified at dc. 7.5 electrical characteristics minimum and maximum specifications apply from t a = ? 40 c to +125 c. typical specifications are at t a = 25 c. all specifications are at avdd = 5 v, avss = 0 v, dvdd = 3.3 v, v ref = 2.5 v, f clk = 7.3728 mhz, pga mode, gain = 1, and data rate = 20 sps (unless otherwise noted). parameter test conditions min typ max unit analog inputs absolute input current pga mode, v (ainx) = 2.5 v 4 6 na pga bypass 200 absolute input current drift 0.01 na/ c differential input current pga mode, v in = 2.5 v ? 3 1 3 na pga mode, chop mode (1) 5 pga bypass, v in = 2.5 v 40 differential input current drift 0.05 na/ c differential input impedance pga mode 1 g pga bypass 50 m crosstalk 0.1 v/v pga gain settings 1, 2, 4, 8, 16, 32, 64, 128 v/v antialias filter frequency c capp, capn = 4.7 nf 60 khz performance dr data rate 2.5 40000 sps noise performance see table 1 inl integral non-linearity gain = 1 to 16 ? 10 2 10 ppm fsr gain = 32 ? 12 3 12 gain = 64 and 128 7 gain = 1 to 32 (40 ksps) 5 v os offset voltage t a = 25 c ? 175 / gain ? 5 50 / gain 175 / gain + 5 v chop mode ? 0.5 / gain ? 0.05 0.2 / gain 0.5 / gain + 0.05 after calibration on the level of noise offset voltage drift gain = 1 to 8 100 / gain 350 / gain nv/ c gain = 16 to 128 10 50 chop mode, gain = 1 to 128 1 5 ge gain error t a = 25 c, gain = 1 to 128 ? 0.5% 0.05% 0.5% after calibration on the level of noise gain drift gain = 1 to 128 0.5 4 ppm/ c nmrr normal-mode rejection ratio (2) see table 7 cmrr common-mode rejection ratio (3) data rate = 20 sps 130 db data rate = 400 sps 105 115 psrr power-supply rejection ratio (4) avdd and avss 90 100 db dvdd 100 120 internal oscillator f clk frequency 2.5 sps to 25.6 ksps 7.3728 mhz 40 ksps 10.24 accuracy ? 2% 0.5% 2%
8 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated electrical characteristics (continued) minimum and maximum specifications apply from t a = ? 40 c to +125 c. typical specifications are at t a = 25 c. all specifications are at avdd = 5 v, avss = 0 v, dvdd = 3.3 v, v ref = 2.5 v, f clk = 7.3728 mhz, pga mode, gain = 1, and data rate = 20 sps (unless otherwise noted). parameter test conditions min typ max unit voltage reference inputs reference input current 300 na input current vs voltage v ref = 0.9 v to 4.8 v 100 na/v input current drift 0.1 na//v/ c input impedance differential 5 m internal voltage reference voltage 2.5 v initial accuracy t a = 25 c 0.2% temperature drift 10 40 ppm/ c output current ? 10 10 ma load regulation 50 v/ma start-up time settling time to 0.001% of final value 100 ms excitation current sources (idacs) current settings 50, 100, 250, 500, 750, 1000, 1500, 2000, 2500, 3000 a compliance range avss avdd ? 1.1 v accuracy ? 4% 0.7% 4% match error same current magnitudes ? 1% 0.1% 1% different current magnitudes 1% temperature drift absolute 50 ppm/ c match drift, i idac1 = i idac2 5 25 level-shift voltage (vbias) voltage (avdd + avss) / 2 v output impedance 100 burn-out current sources current settings sink and source 0.05, 0.2, 1, 10 a accuracy 0.05 a range 0.025 0.05 0.075 a temperature sensor sensor voltage t a = 25 c 122.4 mv temperature coefficient 420 v/ c monitors pga output low avss + 0.2 v high avdd ? 0.2 reference voltage low 0.4 0.6 v
9 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated electrical characteristics (continued) minimum and maximum specifications apply from t a = ? 40 c to +125 c. typical specifications are at t a = 25 c. all specifications are at avdd = 5 v, avss = 0 v, dvdd = 3.3 v, v ref = 2.5 v, f clk = 7.3728 mhz, pga mode, gain = 1, and data rate = 20 sps (unless otherwise noted). parameter test conditions min typ max unit (5) gpio voltage with respect to avss. (6) clkin input stopped. general-purpose inputs/outputs (gpios) (5) v ol low-level output voltage i ol = ? 1 ma 0.2 avdd v v oh high-level output voltage i oh = 1 ma 0.8 avdd v v il low-level input voltage 0.3 avdd v v ih high-level input voltage 0.7 avdd v input hysteresis 0.5 v digital inputs/outputs (other than gpios) v ol low-level output voltage i ol = ? 1 ma 0.2 dvdd v i ol = ? 8 ma 0.2 dvdd v oh high-level output voltage i oh = 1 ma 0.8 dvdd v i oh = 8 ma 0.75 dvdd v il low-level input voltage 0.3 dvdd v v ih high-level input voltage 0.7 dvdd v input hysteresis 0.1 v input leakage v ih or v il ? 10 10 a power supply i avdd i avss analog supply current pga bypass 2.7 4.5 ma pga mode, gain = 1 to 32 3.8 6 pga mode, gain = 64 or 128 4.3 6.5 power-down mode 2 8 a i avdd i avss analog supply current (by function) voltage reference 0.2 ma 40000 sps mode 0.5 current sources as programmed i dvdd digital supply current 20 sps 0.4 0.65 ma 40000 sps 0.6 0.85 power-down mode (6) 30 50 a p d power dissipation pga mode 20 32 mw power-down mode 0.1 0.2
10 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated (1) cs can be tied low. (2) serial interface time-out mode: minimum sclk frequency = 1 khz. otherwise, no minimum sclk frequency. 7.6 timing requirements over operating ambient temperature range, dvdd = 2.7 v to 5.25 v, and dout/ drdy load: 20 pf || 100 k to dgnd (unless otherwise noted) min max unit serial interface t d(cssc) delay time, first sclk rising edge after cs falling edge (1) 50 ns t su(di) setup time, din valid before sclk falling edge 25 ns t h(di) hold time, din valid after sclk falling edge 25 ns t c(sc) sclk period (2) 97 10 6 ns t w(sch), t w(scl) pulse duration, sclk high or low 40 ns t d(sccs) delay time, last sclk falling edge before cs rising edge 50 ns t w(csh) pulse duration, cs high to reset interface 25 ns t d(scir) delay time, sclk high or low to force interface auto-reset 65540 1/f clk reset t w(rstl) pulse duration, reset low 4 1/f clk conversion control t w(sth) pulse duration, start high 4 1/f clk t w(stl) pulse duration, start low 4 1/f clk t su(drst) setup time, start low or stop command after drdy low to stop next conversion (continuous mode) 100 1/f clk t h(drsp) hold time, start low or stop command after drdy low to continue next conversion (continuous mode) 150 1/f clk .
11 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 7.7 switching characteristics over operating ambient temperature range, dvdd = 2.7 v to 5.25 v, and dout/ drdy load: 20 pf || 100 k to dgnd (unless otherwise noted) parameter min typ max unit serial interface t w(drh) pulse duration, drdy high 16 1/f clk t p(csdo) propagation delay time, cs falling edge to dout/ drdy driven 0 50 ns t p(scdo1) propagation delay time, sclk rising edge to valid dout/ drdy 40 ns t h(scdo1) hold time, sclk rising edge to invalid data on dout/ drdy 0 ns t h(scdo2) hold time, last sclk falling edge of operation to invalid data on dout/ drdy 30 ns t p(scdo2) propagation delay time, last sclk falling edge to valid data ready function on dout/ drdy 90 ns t p(csdoz) propagation delay time, cs rising edge to dout/ drdy high impedance 50 ns reset t p(rscn) propagation delay time, reset rising edge or reset command to start of conversion 512 1/f clk t p(prcm) propagation delay time, power-on threshold voltage to adc communication 2 16 1/f clk t p(cmcn) propagation delay time, adc communication to conversion start 512 1/f clk ac excitation t d(acx) delay time, phase-to-phase blanking period 8 1/f clk t c(acx) acx period 2 t stdr conversion control t p(stdr) propagation delay time, start high or start command to drdy high 2 1/f clk figure 1. serial interface timing requirements cs sclk din t w(csh) t c(sc) t w(sch) t su(di) t h(di) t w(scl) t d(sccs) t d(cssc)
12 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated figure 2. serial interface switching characteristics figure 3. serial interface auto-reset characteristics figure 4. conversion control timing requirements sclk cs dout/drdy t p(csdo) t p(csdoz) t h(scdo1) t p(scdo1) data drdy t w(drh) drdy (1) before the first sclk rising edge and after the last sclk falli ng edge of a command, the function of dout/drdy is data re ady. drdy (1) (1) t h(scdo2) t p(scdo2) serial interface auto-reset sclk t d(scir) b7 b6 b5 b4 b3 b2 b1 b0 next byte transaction serial command start stop start drdy t w(sth) t w(stl) t p(stdr) t su(drst) t h(drsp) stop
13 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated figure 5. power-up characteristics figure 6. reset pin and reset command timing requirements figure 7. ac-excitation timing characteristics figure 8. timing voltage-level reference avdd - avss 1 v (typ) 3.5 v (typ) drdy begin adc communication dvdd 1 v (typ) dout/drdy start of 1 st conversion conversion status v bypass all supplies reach thresholds t p(cmcn) t p(prcm) acx1 acx1 acx2 acx2 t d(acx) t d(acx) t c(acx) reset t w(rstl) conversion status t p(rscn) reset start reset command dvdd dgnd ? dvdd 50% t d , t h , t p, t w, t c
14 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 7.8 typical characteristics at t a = 25 c, avdd = 5 v, avss = 0 v, dvdd = 3.3 v, v ref = 2.5 v, data rate = 20 sps, f clk = 7.3728 mhz (f clk = 10.24 mhz for data rate = 40 ksps), and gain = 1 (unless otherwise noted) after calibration, shorted input figure 9. offset voltage vs temperature chop mode, after calibration, shorted input figure 10. offset voltage vs temperature shorted input, 30 units figure 11. offset voltage drift distribution chop mode, shorted input, 30 units figure 12. offset voltage drift distribution after calibration figure 13. offset voltage vs reference voltage after calibration figure 14. gain error vs temperature v ref (v) offset voltage ( p v) 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 -10 -5 0 5 10 15 20 25 30 35 40 d001 gain = 1, 400 sps gain = 1, 40000 sps gain = 16, 400 sps gain = 16, 40000 sps gain = 128, 400 sps gain = 128, 40000 temperature ( q c) offset voltage ( p v) -40 -20 0 20 40 60 80 100 120 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 d010 pga bypass gain = 1 gain = 2 gain = 4 gain = 8 gain = 16 gain = 32 gain = 64 gain = 128 temperature ( q c) offset voltage ( p v) -40 -20 0 20 40 60 80 100 120 -10 -8 -6 -4 -2 0 2 4 6 8 10 d009 pga bypass gain = 1 gain = 2 gain = 4 gain = 8 gain = 16 gain = 32 gain = 64 gain = 128 input-referred offset drift (nv/ q c) population (%) 0 10 20 30 40 50 60 70 80 90 100 0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3 3.3 3.6 d011 gain = 1 gain = 16 gain = 128 input-referred offset drift (nv/ q c) population (%) 0 10 20 30 40 50 60 70 80 90 100 0 20 40 60 80 100 120 140 160 180 200 220 240 d012 gain = 1 gain = 16 gain = 128 temperature ( q c) gain error (ppm) -40 -20 0 20 40 60 80 100 120 -100 -50 0 50 100 150 200 d014 pga bypass gain = 1 gain = 2 gain = 4 gain = 8 gain = 16 gain = 32 gain = 64 gain = 128
15 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated typical characteristics (continued) at t a = 25 c, avdd = 5 v, avss = 0 v, dvdd = 3.3 v, v ref = 2.5 v, data rate = 20 sps, f clk = 7.3728 mhz (f clk = 10.24 mhz for data rate = 40 ksps), and gain = 1 (unless otherwise noted) 30 units figure 15. gain error drift distributions after calibration figure 16. gain error vs reference voltage 20 sps, sinc4 figure 17. noise vs temperature 7200 sps, sinc1 figure 18. noise vs temperature 40000 sps, sinc5 figure 19. noise vs temperature figure 20. noise vs reference voltage v ref (v) gain error (ppm) 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 -40 -30 -20 -10 0 10 20 30 40 50 60 d002 gain = 1, 400 sps gain = 1, 40000 sps gain = 128, 400 sps gain = 128, 40000 sps v ref (v) input-referred noise ( p v rms ) 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 0.07 1 10 100 800800 d006 gain = 1, 400 sps gain = 128, 400 sps gain = 1, 7200 sps gain = 128, 7200 sps gain = 1, 40000 sps gain = 128, 40000 sps temperature ( q c) input-referred noise ( p v rms ) -40 -20 0 20 40 60 80 100 120 0 5 10 15 20 25 30 35 40 45 50 d005 gain = 1 gain = 2 gain = 4 gain = 8 gain = 16 gain = 32 gain = 64 gain = 128 temperature ( q c) input-referred noise ( p v rms ) -40 -20 0 20 40 60 80 100 120 0 1 2 3 4 5 6 7 8 9 10 d004 gain = 1 gain = 2 gain = 4 gain = 8 gain = 16 gain = 32 gain = 64 gain = 128 temperature ( q c) input-referred noise ( p v rms ) -40 -20 0 20 40 60 80 100 120 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 exced003 gain = 1 gain = 2 gain = 4 gain = 8 gain = 16 gain = 32 gain = 64 gain = 128 gain drift (ppm/ q c) population (%) 0 10 20 30 40 50 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 d013 gain = 1 gain = 8 gain = 128
16 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated typical characteristics (continued) at t a = 25 c, avdd = 5 v, avss = 0 v, dvdd = 3.3 v, v ref = 2.5 v, data rate = 20 sps, f clk = 7.3728 mhz (f clk = 10.24 mhz for data rate = 40 ksps), and gain = 1 (unless otherwise noted) 20 sps, gain = 4, 256 data points figure 21. conversion data histogram 20 sps, gain = 128, 256 data points figure 22. conversion data histogram 7200 sps, gain = 4, 8192 data points figure 23. conversion data histogram 7200 sps, gain = 128, 8192 data points figure 24. conversion data histogram figure 25. integral non-linearity vs v in figure 26. integral non-linearity vs temperature full scale range (%v in ) integral non-linearity error (ppm fsr ) -100 -80 -60 -40 -20 0 20 40 60 80 100 -10 -8 -6 -4 -2 0 2 4 6 8 10 d033 gain = 1 gain = 4 gain = 16 gain = 32 temperature ( q c) integral non-linearity (ppm fsr ) -40 -20 0 20 40 60 80 100 120 0 2 4 6 8 10 12 14 16 18 20 d007 gain = 1 gain = 4 gain = 16 gain = 128 conversion data ( p v) population (# of data points) 0 20 40 60 80 100 -12 -10 -8 -6 -4 -2 02 4 6 8 10 12 d030 conversion data ( p v) population (# of data points) 0 20 40 60 80 100 120 140 -3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3 d031 conversion data ( p v) population (# of data points) 0 20 40 60 80 100 120 140 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 d028 conversion data ( p v) population (# of data points) 0 20 40 60 80 100 120 140 160 -0.25 -0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2 0.25 d029
17 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated typical characteristics (continued) at t a = 25 c, avdd = 5 v, avss = 0 v, dvdd = 3.3 v, v ref = 2.5 v, data rate = 20 sps, f clk = 7.3728 mhz (f clk = 10.24 mhz for data rate = 40 ksps), and gain = 1 (unless otherwise noted) 30 units figure 27. integral non-linearity distribution figure 28. integral non-linearity vs reference voltage v refn = avss figure 29. reference input current vs reference voltage 30 units figure 30. temperature sensor voltage histogram 30 units figure 31. internal oscillator vs temperature figure 32. operating current vs temperature integral non-linearity (ppm fsr ) population (%) 0 10 20 30 40 50 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 d015 gain = 1 gain = 4 gain = 32 v ref (v) integral non-linearity (ppm fsr ) 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 0 3 6 9 12 15 d008 gain = 1, 20 sps gain = 4, 20 sps gain = 32, 20 sps gain = 1, 40000 sps gain = 4, 40000 sps gain = 32, 40000 sps v ref (v) reference input current (na) 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 -50 0 50 100 150 200 250 300 350 400 450 500 550 refn refp d024 t a = -40 q c t a = 25 q c t a = 85 q c t a = 125 q c temperature sensor voltage (mv) population (%) 0 10 20 30 40 121 121.4 121.8 122.2 122.6 123 123.4 123.8 124.2 d017 temperature ( q c) operating current (ma) -40 -20 0 20 40 60 80 100 120 0 1 2 3 4 5 6 d018 i avdd , i avss (gain d 32) i avdd , i avss (gain t 64) i dvdd (20 sps) i dvdd (40000 sps) temperature ( q c) internal oscillator error (%) -40 -20 0 20 40 60 80 100 120 -1.5 -1 -0.5 0 0.5 1 d016
18 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated typical characteristics (continued) at t a = 25 c, avdd = 5 v, avss = 0 v, dvdd = 3.3 v, v ref = 2.5 v, data rate = 20 sps, f clk = 7.3728 mhz (f clk = 10.24 mhz for data rate = 40 ksps), and gain = 1 (unless otherwise noted) figure 33. pga high monitor threshold figure 34. pga low monitor threshold figure 35. reference voltage low alarm threshold figure 36. cmrr and psrr vs temperature i idac = 50 a figure 37. idac current vs idac voltage i idac = 250 a figure 38. idac current vs idac voltage temperature ( q c) reference low monitor threshold (v) -40 -20 0 20 40 60 80 100 120 0 0.2 0.4 0.6 0.8 1 d027 temperature ( q c) cmrr and psrr (db) -40 -20 0 20 40 60 80 100 120 80 85 90 95 100 105 110 115 120 125 130 d034 cmrr psrr avdd, avss psrr dvdd idac voltage (v) idac current ( p a) 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 40 42.5 45 47.5 50 52.5 55 d022 t a = -40 q c t a = 25 q c t a = 85 q c t a = 125 q c idac voltage (v) idac current ( p a) 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 200 210 220 230 240 250 260 d019 t a = -40 q c t a = 25 q c t a = 85 q c t a = 125 q c temperature ( q c) pga low monitor threshold (v) -40 -20 0 20 40 60 80 100 120 0 0.05 0.1 0.15 0.2 0.25 0.3 d026 temperature ( q c) pga high monitor threshold (v) -40 -20 0 20 40 60 80 100 120 4.7 4.75 4.8 4.85 4.9 4.95 5 d025
19 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated typical characteristics (continued) at t a = 25 c, avdd = 5 v, avss = 0 v, dvdd = 3.3 v, v ref = 2.5 v, data rate = 20 sps, f clk = 7.3728 mhz (f clk = 10.24 mhz for data rate = 40 ksps), and gain = 1 (unless otherwise noted) i idac = 1000 a figure 39. idac current vs idac voltage i idac = 3000 a figure 40. idac current vs idac voltage i idac1 = i idac2 = 250 a figure 41. idac current match vs idac voltage i idac1 = i idac2 = 1000 a figure 42. idac current match vs idac voltage idac voltage (v) idac match error (%) 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 -0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2 d035 t a = -40 q c t a = 25 q c t a = 85 q c t a = 125 q c idac voltage (v) idac current ( p a) 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 800 850 900 950 1000 1050 d020 t a = -40 q c t a = 25 q c t a = 85 q c t a = 125 q c idac voltage (v) idac current ( p a) 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 2800 2850 2900 2950 3000 3050 d021 t a = -40 q c t a = 25 q c t a = 85 q c t a = 125 q c idac voltage (v) idac match error (%) 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 -0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2 d023 t a = -40 q c t a = 25 q c t a = 85 q c t a = 125 q c
20 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 8 parameter measurement information 8.1 noise performance the ads126x noise performance depends on the adc configuration: data rate, pga gain, digital filter configuration, and chop mode. the combination of the parameters affect noise performance. two significant factors affecting noise performance are data rate and pga gain. since the profile of noise is predominantly white (flat vs frequency), decreasing the data rate proportionally decreases bandwidth and therefore, total noise. since the noise of the pga is lower than that of the modulator of the adc, increasing the gain reduces noise when treated as an input-referred quantity. noise performance also depends on the digital filter and chop mode. as the order of the digital filter increases, the noise bandwidth correspondingly decreases resulting in lower noise. further, as a result of two-point data averaging in chop mode, noise performance improves by 2 compared to normal operation. table 1 shows noise performance in units of v rms (rms = root mean square) under the conditions listed. the values in parenthesis are peak-to-peak values. table 2 shows the noise performance in effective resolution (bits) under the specified conditions. the values shown in parenthesis are the noise-free resolution. noise-free resolution is the resolution of the adc with no code flicker. the noise-free resolution data are calculated based on the peak-to-peak noise measurements. the effective resolution data listed in the tables are calculated using equation 1 : effective resolution or noise-free resolution = ln (fsr / e n ) / ln (2) where ? fsr = full scale range = 2 v ref / gain (see recommended operating conditions for fsr) ? e n = input referred voltage noise (rms value to calculate effective resolution, p-p value to calculate noise-free resolution) (1) the data shown in the noise performance table represent typical adc performance at t a = 25 c. the noise- performance data are the standard deviation and peak-to-peak computations of the adc data. the noise data are acquired with inputs shorted, based on consecutive adc readings for a period of ten seconds or 8192 data points, whichever occurs first. because of the statistical nature of noise, repeated noise measurements may yield higher or lower noise performance results. table 1. noise in v rms ( v pp ) at t a = 25 c and internal v ref = 2.5 v data rate filter gain 1 2 4 8 16 32 64 128 2.5 sps fir 0.18 (0.6) 0.078 (0.28) 0.046 (0.16) 0.025 (0.096) 0.014 (0.053) 0.012 (0.045) 0.01 (0.042) 0.01 (0.04) 2.5 sps sinc1 0.15 (0.47) 0.071 (0.28) 0.038 (0.14) 0.019 (0.075) 0.012 (0.051) 0.01 (0.039) 0.009 (0.037) 0.009 (0.037) 2.5 sps sinc2 0.14 (0.38) 0.065 (0.23) 0.032 (0.096) 0.018 (0.059) 0.011 (0.037) 0.007 (0.028) 0.007 (0.028) 0.008 (0.033) 2.5 sps sinc3 0.12 (0.38) 0.062 (0.17) 0.028 (0.064) 0.016 (0.053) 0.01 (0.035) 0.008 (0.027) 0.007 (0.026) 0.006 (0.023) 2.5 sps sinc4 0.1 (0.26) 0.059 (0.17) 0.032 (0.085) 0.016 (0.059) 0.010 (0.035) 0.008 (0.027) 0.006 (0.025) 0.006 (0.024) 5 sps fir 0.22 (0.89) 0.11 (0.4) 0.058 (0.24) 0.032 (0.13) 0.021 (0.085) 0.016 (0.065) 0.014 (0.061) 0.015 (0.066) 5 sps sinc1 0.18 (0.6) 0.093 (0.36) 0.047 (0.17) 0.025 (0.11) 0.017 (0.069) 0.014 (0.061) 0.012 (0.054) 0.014 (0.063) 5 sps sinc2 0.16 (0.64) 0.084 (0.32) 0.043 (0.16) 0.023 (0.085) 0.015 (0.064) 0.011 (0.047) 0.010(0.046) 0.011 (0.049) 5 sps sinc3 0.13 (0.51) 0.088 (0.32) 0.036 (0.15) 0.024 (0.091) 0.014 (0.053) 0.01 (0.043) 0.009 (0.045) 0.009 (0.042) 5 sps sinc4 0.13 (0.51) 0.077 (0.28) 0.034 (0.12) 0.021 (0.075) 0.013 (0.053) 0.010 (0.044) 0.008 (0.038) 0.009 (0.038) 10 sps fir 0.27 (1.4) 0.14 (0.72) 0.076 (0.4) 0.042 (0.21) 0.029 (0.15) 0.023 (0.12) 0.023 (0.11) 0.022 (0.11) 10 sps sinc1 0.23 (1.1) 0.13 (0.57) 0.064 (0.3) 0.036 (0.19) 0.024 (0.13) 0.02 (0.1) 0.018 (0.083) 0.018 (0.089) 10 sps sinc2 0.2 (0.89) 0.11 (0.51) 0.054 (0.24) 0.03 (0.14) 0.019 (0.093) 0.015 (0.075) 0.015 (0.079) 0.016 (0.077) 10 sps sinc3 0.18 (0.81) 0.097 (0.38) 0.05 (0.22) 0.028 (0.14) 0.019 (0.088) 0.015 (0.063) 0.013 (0.067) 0.013 (0.065) 10 sps sinc4 0.17 (0.68) 0.099 (0.45) 0.049 (0.24) 0.024 (0.12) 0.018 (0.085) 0.013 (0.063) 0.012 (0.061) 0.012 (0.062) 16.6 sps sinc1 0.3 (1.4) 0.16 (0.81) 0.082 (0.43) 0.048 (0.25) 0.031 (0.17) 0.025 (0.15) 0.024 (0.12) 0.024 (0.14) 16.6 sps sinc2 0.24 (1.2) 0.13 (0.64) 0.067 (0.34) 0.038 (0.2) 0.026 (0.14) 0.021 (0.11) 0.019 (0.099) 0.019 (0.098) 16.6 sps sinc3 0.22 (0.98) 0.12 (0.64) 0.065 (0.3) 0.036 (0.18) 0.024 (0.12) 0.019 (0.095) 0.017 (0.092) 0.018 (0.093) 16.6 sps sinc4 0.21 (1.1) 0.12 (0.53) 0.06 (0.29) 0.035 (0.18) 0.022 (0.11) 0.017 (0.084) 0.016 (0.085) 0.016 (0.086)
21 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated noise performance (continued) table 1. noise in v rms ( v pp ) at t a = 25 c and internal v ref = 2.5 v (continued) data rate filter gain 1 2 4 8 16 32 64 128 20 sps fir 0.37 (2) 0.2 (1.1) 0.1 (0.56) 0.059 (0.34) 0.041 (0.22) 0.034 (0.18) 0.029 (0.17) 0.03 (0.15) 20 sps sinc1 0.32 (1.8) 0.18 (0.92) 0.091 (0.48) 0.051 (0.26) 0.034 (0.2) 0.028 (0.15) 0.025 (0.14) 0.025 (0.14) 20 sps sinc2 0.27 (1.4) 0.15 (0.77) 0.073 (0.35) 0.042 (0.22) 0.027 (0.14) 0.022 (0.13) 0.021 (0.11) 0.02 (0.11) 20 sps sinc3 0.24 (1.2) 0.13 (0.64) 0.069 (0.35) 0.039 (0.21) 0.026 (0.14) 0.02 (0.11) 0.018 (0.099) 0.018 (0.1) 20 sps sinc4 0.23 (1.1) 0.13 (0.66) 0.066 (0.33) 0.037 (0.19) 0.024 (0.12) 0.018 (0.095) 0.017 (0.095) 0.017 (0.099) 50 sps sinc1 0.49 (2.9) 0.27 (1.6) 0.14 (0.83) 0.08 (0.5) 0.053 (0.31) 0.043 (0.25) 0.039 (0.23) 0.038 (0.23) 50 sps sinc2 0.4 (2.3) 0.22 (1.3) 0.11 (0.69) 0.064 (0.38) 0.043 (0.27) 0.035 (0.22) 0.033 (0.2) 0.032 (0.2) 50 sps sinc3 0.37 (2.2) 0.2 (1.2) 0.11 (0.64) 0.058 (0.35) 0.04 (0.25) 0.033 (0.19) 0.029 (0.18) 0.03 (0.18) 50 sps sinc4 0.34 (2) 0.19 (1.1) 0.098 (0.61) 0.056 (0.32) 0.036 (0.23) 0.03 (0.17) 0.028 (0.17) 0.028 (0.17) 60 sps sinc1 0.55 (3.3) 0.28 (1.9) 0.15 (0.88) 0.087 (0.53) 0.058 (0.34) 0.047 (0.28) 0.044 (0.29) 0.042 (0.26) 60 sps sinc2 0.45 (2.7) 0.24 (1.4) 0.12 (0.71) 0.07 (0.45) 0.048 (0.32) 0.039 (0.25) 0.036 (0.21) 0.035 (0.21) 60 sps sinc3 0.41 (2.7) 0.21 (1.3) 0.11 (0.68) 0.065 (0.4) 0.044 (0.25) 0.036 (0.23) 0.032 (0.19) 0.031 (0.19) 60 sps sinc4 0.37 (2) 0.2 (1.1) 0.11 (0.6) 0.059 (0.36) 0.041 (0.25) 0.033 (0.21) 0.03 (0.18) 0.03 (0.17) 100 sps sinc1 0.69 (4.5) 0.37 (2.4) 0.19 (1.3) 0.11 (0.73) 0.075 (0.5) 0.06 (0.39) 0.056 (0.37) 0.056 (0.38) 100 sps sinc2 0.56 (3.5) 0.3 (1.9) 0.16 (0.97) 0.09 (0.55) 0.062 (0.39) 0.051 (0.32) 0.046 (0.31) 0.045 (0.29) 100 sps sinc3 0.51 (3.4) 0.27 (1.8) 0.14 (0.9) 0.083 (0.51) 0.056 (0.36) 0.045 (0.3) 0.041 (0.27) 0.041 (0.25) 100 sps sinc4 0.48 (3.3) 0.26 (1.6) 0.14 (0.87) 0.078 (0.48) 0.053 (0.34) 0.043 (0.27) 0.039 (0.24) 0.039 (0.26) 400 sps sinc1 1.4 (9.6) 0.72 (5.4) 0.38 (2.7) 0.22 (1.6) 0.15 (1.1) 0.12 (0.85) 0.11 (0.85) 0.11 (0.79) 400 sps sinc2 1.1 (8.2) 0.58 (4.2) 0.31 (2.3) 0.18 (1.3) 0.12 (0.9) 0.099 (0.74) 0.091 (0.65) 0.091 (0.69) 400 sps sinc3 1 (7.4) 0.53 (3.7) 0.28 (2) 0.17 (1.2) 0.11 (0.8) 0.09 (0.66) 0.083 (0.61) 0.083 (0.59) 400 sps sinc4 0.95 (6.9) 0.51 (3.6) 0.27 (1.9) 0.15 (1.2) 0.1 (0.7) 0.084 (0.58) 0.077 (0.55) 0.077 (0.57) 1200 sps sinc1 2.3 (17) 1.2 (9.2) 0.64 (5) 0.37 (2.9) 0.25 (1.9) 0.2 (1.6) 0.19 (1.4) 0.19 (1.5) 1200 sps sinc2 1.9 (14) 1 (7.6) 0.54 (3.9) 0.31 (2.4) 0.21 (1.6) 0.17 (1.3) 0.16 (1.2) 0.16 (1.2) 1200 sps sinc3 1.8 (13) 0.92 (7) 0.49 (3.7) 0.29 (2.2) 0.19 (1.4) 0.16 (1.2) 0.14 (1.1) 0.14 (1.1) 1200 sps sinc4 1.6 (12) 0.86 (6.4) 0.46 (3.6) 0.27 (2) 0.18 (1.4) 0.15 (1.1) 0.13 (1) 0.13 (1) 2400 sps sinc1 3.2 (25) 1.7 (13) 0.88 (6.7) 0.51 (3.9) 0.35 (2.7) 0.28 (2.2) 0.26 (2) 0.26 (2) 2400 sps sinc2 2.7 (21) 1.4 (10) 0.76 (5.8) 0.44 (3.3) 0.3 (2.2) 0.24 (1.9) 0.22 (1.6) 0.22 (1.6) 2400 sps sinc3 2.5 (19) 1.3 (9.8) 0.69 (5.2) 0.4 (3) 0.27 (2.1) 0.22 (1.7) 0.2 (1.6) 0.2 (1.5) 2400 sps sinc4 2.3 (17) 1.2 (9.4) 0.65 (4.9) 0.37 (2.8) 0.25 (2) 0.21 (1.5) 0.19 (1.5) 0.19 (1.4) 4800 sps sinc1 4.3 (33) 2.3 (17) 1.2 (9.4) 0.69 (5.2) 0.46 (3.5) 0.37 (2.9) 0.34 (2.6) 0.34 (2.6) 4800 sps sinc2 3.8 (29) 2 (15) 1.1 (8.5) 0.61 (4.7) 0.41 (3.1) 0.33 (2.6) 0.31 (2.3) 0.3 (2.3) 4800 sps sinc3 3.5 (27) 1.8 (14) 0.97 (7.2) 0.56 (4.1) 0.38 (3) 0.31 (2.4) 0.28 (2.1) 0.28 (2.2) 4800 sps sinc4 3.3 (25) 1.7 (13) 0.92 (7.1) 0.53 (4.1) 0.36 (2.7) 0.29 (2.2) 0.27 (2.1) 0.27 (1.9) 7200 sps sinc1 5 (38) 2.6 (20) 1.4 (10) 0.8 (6) 0.53 (4) 0.43 (3.2) 0.39 (2.9) 0.39 (2.9) 7200 sps sinc2 4.6 (35) 2.4 (19) 1.3 (9.9) 0.73 (5.4) 0.49 (3.8) 0.39 (2.9) 0.36 (2.8) 0.36 (2.7) 7200 sps sinc3 4.3 (33) 2.2 (17) 1.2 (9.3) 0.68 (5) 0.46 (3.6) 0.37 (2.8) 0.34 (2.5) 0.34 (2.6) 7200 sps sinc4 4.1 (31) 2.1 (15) 1.1 (8.8) 0.65 (5) 0.44 (3.3) 0.35 (2.6) 0.33 (2.5) 0.32 (2.5) 14400 sps sinc5 6 (47) 3.1 (24) 1.7 (13) 0.93 (7.1) 0.61 (4.9) 0.49 (3.8) 0.45 (3.5) 0.45 (3.4) 19200 sps sinc5 8.5 (67) 4.3 (34) 2.3 (17) 1.2 (9.6) 0.77 (6) 0.57 (4.3) 0.54 (4) 0.53 (4.1) 25600 sps sinc5 19 (140) 9.5 (73) 4.8 (37) 2.5 (18) 1.3 (10) 0.83 (6.3) 0.8 (6) 0.81 (6) 40000 sps sinc5 30 (220) 15 (110) 7.7 (56) 3.9 (29) 2 (15) 1.2 (9.4) 1.2 (8.9) 1.2 (9)
22 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated table 2. effective resolution (noise-free resolution) at t a = 25 c and v ref = 5 v data rate filter gain 1 2 4 8 16 32 64 128 2.5 sps fir 24 (24) 24 (23.9) 24 (23.7) 24 (23.5) 24 (23.3) 24 (22.5) 23.7 (21.6) 22.7 (20.7) 2.5 sps sinc1 24 (24) 24 (23.9) 24 (23.9) 24 (23.8) 24 (23.4) 24 (22.8) 23.8 (21.8) 22.8 (20.8) 2.5 sps sinc2 24 (24) 24 (24) 24 (24) 24 (24) 24 (23.8) 24 (23.2) 24 (22.2) 23 (21) 2.5 sps sinc3 24 (24) 24 (24) 24 (24) 24 (24) 24 (23.9) 24 (23.3) 24 (22.3) 23.5 (21.5) 2.5 sps sinc4 24 (24) 24 (24) 24 (24) 24 (24) 24 (23.9) 24 (23.3) 24 (22.4) 23.5 (21.5) 5 sps fir 24 (23.4) 24 (23.4) 24 (23.1) 24 (23) 24 (22.6) 24 (22) 23.2 (21.1) 22.1 (20) 5 sps sinc1 24 (24) 24 (23.5) 24 (23.6) 24 (23.3) 24 (22.9) 24 (22.1) 23.4 (21.3) 22.3 (20.1) 5 sps sinc2 24 (23.9) 24 (23.7) 24 (23.7) 24 (23.6) 24 (23) 24 (22.5) 23.7 (21.5) 22.6 (20.4) 5 sps sinc3 24 (24) 24 (23.7) 24 (23.8) 24 (23.5) 24 (23.3) 24 (22.6) 23.8 (21.5) 22.8 (20.6) 5 sps sinc4 24 (24) 24 (23.9) 24 (24) 24 (23.8) 24 (23.3) 24 (22.6) 24 (21.8) 22.9 (20.8) 10 sps fir 24 (22.8) 24 (22.5) 24 (22.4) 24 (22.3) 24 (21.8) 23.5 (21.2) 22.5 (20.2) 21.6 (19.3) 10 sps sinc1 24 (23.1) 24 (22.9) 24 (22.8) 24 (22.5) 24 (22) 23.7 (21.4) 22.9 (20.7) 21.9 (19.6) 10 sps sinc2 24 (23.4) 24 (23) 24 (23.1) 24 (22.9) 24 (22.5) 24 (21.8) 23.1 (20.7) 22.1 (19.8) 10 sps sinc3 24 (23.6) 24 (23.5) 24 (23.2) 24 (22.9) 24 (22.6) 24 (22.1) 23.3 (21) 22.4 (20) 10 sps sinc4 24 (23.8) 24 (23.2) 24 (23.1) 24 (23.1) 24 (22.6) 24 (22.1) 23.4 (21.1) 22.4 (20.1) 16.6 sps sinc1 24 (22.7) 24 (22.4) 24 (22.3) 24 (22.1) 24 (21.6) 23.4 (20.8) 22.5 (20.1) 21.4 (18.9) 16.6 sps sinc2 24 (22.9) 24 (22.7) 24 (22.6) 24 (22.4) 24 (21.9) 23.6 (21.2) 22.8 (20.4) 21.8 (19.4) 16.6 sps sinc3 24 (23.3) 24 (22.7) 24 (22.8) 24 (22.5) 24 (22.1) 23.8 (21.5) 23 (20.5) 21.9 (19.5) 16.6 sps sinc4 24 (23.2) 24 (23) 24 (22.9) 24 (22.6) 24 (22.3) 23.9 (21.6) 23.1 (20.6) 22.1 (19.6) 20 sps fir 24 (22.2) 24 (21.9) 24 (21.9) 24 (21.6) 23.8 (21.2) 23 (20.5) 22.2 (19.7) 21.1 (18.8) 20 sps sinc1 24 (22.4) 24 (22.2) 24 (22.1) 24 (22) 24 (21.4) 23.3 (20.9) 22.4 (19.9) 21.4 (19) 20 sps sinc2 24 (22.8) 24 (22.5) 24 (22.6) 24 (22.2) 24 (21.9) 23.6 (21.1) 22.7 (20.3) 21.7 (19.3) 20 sps sinc3 24 (22.9) 24 (22.7) 24 (22.6) 24 (22.3) 24 (21.9) 23.7 (21.3) 22.9 (20.4) 21.8 (19.4) 20 sps sinc4 24 (23.1) 24 (22.7) 24 (22.7) 24 (22.5) 24 (22.1) 23.8 (21.5) 22.9 (20.5) 22 (19.4) 50 sps sinc1 24 (21.7) 24 (21.4) 23.9 (21.3) 23.7 (21.1) 23.4 (20.8) 22.6 (20.1) 21.7 (19.2) 20.8 (18.2) 50 sps sinc2 24 (22.1) 24 (21.7) 24 (21.6) 24 (21.5) 23.7 (21) 22.9 (20.3) 22 (19.4) 21 (18.4) 50 sps sinc3 24 (22.1) 24 (21.8) 24 (21.7) 24 (21.6) 23.8 (21.1) 23 (20.5) 22.2 (19.6) 21.1 (18.6) 50 sps sinc4 24 (22.2) 24 (22) 24 (21.8) 24 (21.7) 23.9 (21.2) 23.1 (20.6) 22.2 (19.6) 21.3 (18.7) 60 sps sinc1 24 (21.5) 23.9 (21.2) 23.8 (21.2) 23.6 (21) 23.3 (20.6) 22.5 (19.9) 21.6 (18.9) 20.6 (18) 60 sps sinc2 24 (21.8) 24 (21.6) 24 (21.6) 23.9 (21.2) 23.5 (20.7) 22.7 (20.1) 21.9 (19.3) 20.9 (18.3) 60 sps sinc3 24 (21.8) 24 (21.7) 24 (21.6) 24 (21.4) 23.7 (21.1) 22.9 (20.2) 22 (19.4) 21.1 (18.4) 60 sps sinc4 24 (22.3) 24 (21.9) 24 (21.8) 24 (21.5) 23.8 (21.1) 23 (20.3) 22.1 (19.5) 21.1 (18.6) 100 sps sinc1 23.8 (21.1) 23.5 (20.8) 23.4 (20.7) 23.2 (20.5) 22.9 (20.1) 22.1 (19.4) 21.2 (18.5) 20.2 (17.5) 100 sps sinc2 24 (21.4) 23.8 (21.2) 23.8 (21.1) 23.5 (20.9) 23.2 (20.4) 22.4 (19.7) 21.5 (18.8) 20.5 (17.9) 100 sps sinc3 24 (21.5) 23.9 (21.2) 23.9 (21.2) 23.7 (21) 23.3 (20.6) 22.5 (19.8) 21.7 (19) 20.7 (18) 100 sps sinc4 24 (21.5) 24 (21.4) 23.9 (21.3) 23.7 (21.1) 23.4 (20.6) 22.6 (19.9) 21.7 (19.2) 20.8 (18) 400 sps sinc1 22.8 (20) 22.6 (19.6) 22.5 (19.6) 22.3 (19.4) 21.9 (19) 21.1 (18.3) 20.2 (17.3) 19.2 (16.4) 400 sps sinc2 23.1 (20.2) 22.8 (20) 22.7 (19.9) 22.5 (19.7) 22.2 (19.2) 21.4 (18.5) 20.5 (17.7) 19.5 (16.6) 400 sps sinc3 23.2 (20.4) 23 (20.2) 22.9 (20.1) 22.7 (19.8) 22.3 (19.4) 21.5 (18.7) 20.7 (17.8) 19.7 (16.8) 400 sps sinc4 23.3 (20.5) 23 (20.2) 23 (20.2) 22.8 (19.9) 22.4 (19.6) 21.6 (18.9) 20.8 (17.9) 19.8 (16.9) 1200 sps sinc1 22 (19.1) 21.8 (18.9) 21.7 (18.8) 21.5 (18.5) 21.1 (18.1) 20.4 (17.4) 19.5 (16.6) 18.5 (15.5) 1200 sps sinc2 22.3 (19.4) 22.1 (19.1) 22 (19.1) 21.7 (18.8) 21.4 (18.4) 20.6 (17.7) 19.7 (16.8) 18.7 (15.8) 1200 sps sinc3 22.4 (19.5) 22.2 (19.3) 22.1 (19.2) 21.9 (18.9) 21.5 (18.6) 20.8 (17.8) 19.9 (17) 18.9 (16) 1200 sps sinc4 22.5 (19.6) 22.3 (19.4) 22.2 (19.2) 22 (19.1) 21.6 (18.6) 20.9 (17.9) 20 (17.1) 19 (16.1) 2400 sps sinc1 21.6 (18.6) 21.3 (18.4) 21.2 (18.3) 21 (18.1) 20.7 (17.7) 19.9 (16.9) 19 (16.1) 18 (15.1) 2400 sps sinc2 21.8 (18.9) 21.6 (18.7) 21.5 (18.5) 21.3 (18.4) 20.9 (17.9) 20.1 (17.2) 19.2 (16.4) 18.3 (15.3) 2400 sps sinc3 21.9 (19) 21.7 (18.8) 21.6 (18.7) 21.4 (18.5) 21.1 (18) 20.3 (17.3) 19.4 (16.4) 18.4 (15.5) 2400 sps sinc4 22 (19.2) 21.8 (18.8) 21.7 (18.8) 21.5 (18.6) 21.1 (18.1) 20.4 (17.4) 19.5 (16.5) 18.5 (15.6)
23 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated table 2. effective resolution (noise-free resolution) at t a = 25 c and v ref = 5 v (continued) data rate filter gain 1 2 4 8 16 32 64 128 4800 sps sinc1 21.2 (18.2) 20.9 (18) 20.8 (17.8) 20.6 (17.7) 20.3 (17.3) 19.5 (16.5) 18.6 (15.7) 17.6 (14.7) 4800 sps sinc2 21.3 (18.4) 21.1 (18.1) 21 (18) 20.8 (17.8) 20.4 (17.4) 19.7 (16.7) 18.8 (15.8) 17.8 (14.9) 4800 sps sinc3 21.4 (18.5) 21.2 (18.3) 21.1 (18.2) 20.9 (18) 20.6 (17.5) 19.8 (16.8) 18.9 (16) 17.9 (15) 4800 sps sinc4 21.5 (18.6) 21.3 (18.3) 21.2 (18.2) 21 (18) 20.7 (17.6) 19.9 (17) 19 (16) 18 (15.1) 7200 sps sinc1 20.9 (18) 20.7 (17.7) 20.6 (17.7) 20.4 (17.5) 20.1 (17.1) 19.3 (16.4) 18.4 (15.5) 17.4 (14.5) 7200 sps sinc2 21.1 (18.1) 20.8 (17.8) 20.7 (17.8) 20.5 (17.6) 20.2 (17.1) 19.4 (16.5) 18.5 (15.6) 17.5 (14.6) 7200 sps sinc3 21.2 (18.2) 20.9 (18) 20.8 (17.9) 20.6 (17.8) 20.3 (17.2) 19.5 (16.6) 18.6 (15.8) 17.6 (14.7) 7200 sps sinc4 21.2 (18.3) 21 (18.1) 20.9 (17.9) 20.7 (17.8) 20.4 (17.3) 19.6 (16.7) 18.7 (15.8) 17.7 (14.7) 14400 sps sinc5 20.7 (17.7) 20.4 (17.5) 20.3 (17.4) 20.2 (17.2) 19.9 (16.8) 19.1 (16.2) 18.2 (15.3) 17.2 (14.3) 19200 sps sinc5 20.2 (17.2) 19.9 (17) 19.9 (17) 19.8 (16.8) 19.5 (16.5) 18.9 (16) 18 (15.1) 17 (14) 25600 sps sinc5 19 (16.1) 18.8 (15.9) 18.8 (15.9) 18.8 (15.9) 18.7 (15.7) 18.3 (15.4) 17.4 (14.5) 16.4 (13.5) 40000 sps sinc5 18.3 (15.4) 18.1 (15.3) 18.1 (15.3) 18.1 (15.2) 18.1 (15.1) 17.8 (14.8) 16.8 (13.9) 15.8 (12.9)
24 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9 detailed description 9.1 overview the ads1260 and ads1261 are 5-channel and 10-channel, precision 24-bit, delta-sigma ( ) adcs with an integrated analog front end (afe) and voltage reference. the low-noise and low-drift architecture make the adcs suitable for precision measurement of low signal level sensors, such as strain-gauge bridges, pressure transducers and temperature sensors. key features of the adc are: ? very low noise, 1-g input impedance pga ? high-precision, 24-bit adc ? internal oscillator ? 2.5-v voltage reference ? signal and voltage reference monitors ? excitation current sources ? input level-shift voltage ? sensor burn-out current sources ? temperature sensor ? cyclic redundancy check (crc) communication error detection ? two voltage reference inputs (ads1261) ? four gpio with ac-excitation (ads1261) the analog inputs (ainx) connect to the input multiplexer (mux). the adc supports three (five) differential or five (ten) single-ended input configurations for ads1260 and ads1261, respectively. the programmable gain amplifier (pga) follows the input multiplexer. the pga is suitable for direct connection to low-level sensors. the gain is programmable from 1 to 128. the pga bypass option connects the analog inputs directly to the precharge buffered modulator, extending the input voltage range to the power supplies. the pga output connects to pins capp and capn. the adc antialias filter is provided at the pga output with an external capacitor. the pga is monitored to verify linear operation. alarm bits in the status register set if the linear range of the pga is exceeded. a delta-sigma modulator measures the input voltage relative to the reference voltage to produce the 24-bit conversion result. the differential input range of the adc is v ref / gain. the digital filter averages and decimates the modulator output data to yield the final, down-sampled conversion result. the sinc filter is programmable (sinc1 through sinc5) allowing optimization of conversion time, conversion noise and line-cycle rejection. the finite impulse response (fir) filter mode provides single-cycle settled data with simultaneous rejection of 50-hz and 60-hz at data rates of 20 sps or less. the adc reference is either 2.5-v internal, external or the 5-v analog power supply. the refout pin provides the buffered reference voltage output. the external reference is monitored for low or missing voltage. the ads1261 provides two voltage reference inputs, multiplexed with the analog inputs. the adc includes two current sources that provide excitation to resistive sensors (rtd). additionally, the ads1261 provides four gpio control lines. the gpios are used for input and output of general-purpose logic signals, as well as providing drive signals for ac-excited bridges. the gpios are multiplexed to the analog inputs. the temperature sensor and the power supply voltages are read through the multiplexer. the programmable burn-out test currents connect to the multiplexer output. the currents detect failed sensors or faults in the sensor connection. the level-shift voltage on aincom provides the bias for floating sensors. the spi-compatible serial interface is used to read the conversion data and also to configure and control the adc. data communication errors are detected by crc. the serial interface consists of four signals: cs, sclk, din and dout/ drdy. the dual function dout/ drdy provides data output and also the data ready signal. the adc serial interface can be implemented with as little as three pins by tying cs low. the adc clock is either internal or external. the adc detects the external clock automatically. the nominal clock frequency is 7.3728 mhz (10.24 mhz for 40-ksps operation).
25 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated overview (continued) adc conversions are controlled by the start pin or by the start command. the adc is programmable for continuous or one-shot conversions. the drdy or dout/ drdy pin provides the conversion data ready signal. when taken low, the reset pin resets the adc. the adc is powered down by the pwdn pin or is powered down in software mode. the adc operates in either bipolar analog supply configuration ( 2.5 v), or in a single 5-v supply configuration. the digital power supply range is 2.7 v to 5 v. the bypass pin is the internal subregulator output used for the adc digital core. 9.2 functional block diagram 24-bit ? adc input mux digital filter serial interface cs dout/drdy din start reset clock mux clkin refout buf ain0 ain1 level shift avss avdd dvdd dgnd ldo bypass control sensor burn-out currents ain2 ain3 ain4 ain5 ain6 ain7 ain8 aincom ref mux 2.5-v ref capp capn ref monitor pga monitor internal oscillator 2-v digital core sclk temp sensor pga drdy pwdn ads1261 + crc verification ain9 gpio mux avdd ac exc i/o voltage excitation current sources power supply
26 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.3 feature description the following sections describe the functional blocks of the adc. 9.3.1 analog inputs figure 43 shows the analog input circuit consist of esd-protection diodes, the input multiplexer and sensor burn- out current sources. the ads1260 has six analog inputs to support five single-ended measurement channels. the ads1261 has 11 analog inputs to support 10 single-ended measurement channels. both devices have four internal (system) measurements, and an option where no inputs are connected. figure 43. analog input block diagram 9.3.1.1 esd diodes esd diodes are incorporated to protect the adc inputs from possible esd events occurring during the manufacturing process and during pcb assembly when manufactured in an esd-controlled environment. for system-level esd protection, consider the use of external esd protection devices for pins that are exposed to esd, including the analog inputs. if either input is driven below avss ? 0.3 v, or above avdd + 0.3 v, the internal protection diodes may conduct. if these conditions are possible, use external clamp diodes, series resistors, or both to limit the input current to the specified maximum value. 9.3.1.2 input multiplexer the input multiplexer selects the signal for measurement. the multiplexer consists of independent positive and negative sections. see figure 43 for multiplexer register settings. the multiplexers select any input as positive and any input as negative for the pga. because the level-shift voltage connects to aincom (only), aincom is suitable as the common input for single-ended signals that require a level-shift voltage. the switching sequence of the multiplexer is break-before-make in order to reduce charge injection into the next measurement channel. be aware that over-driving unused channels beyond the power supplies can effect conversions taking place on active channels. see the input overload section for more information. aincom temperature sensor avss ain0 ain1 ain2 ain3 ain4 ain5 ain6 ain7 ain8 avdd esd diodes esd diodes 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 (avdd avss) / 4 dvdd / 4 all open 1011 1100 1101 1110 1111 muxp-out pga sensor burn-out currents muxp[3:0] bits 7:4 of inpmux (register address = 11h) muxn[3:0] bits 3:0 of inpmux (register address = 11h) ain9 1010 ads1261 v com : (avdd + avss) / 2 muxn-out + - positive input multiplexer negative input multiplexer
27 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated feature description (continued) 9.3.1.3 temperature sensor the adc has an internal temperature sensor. the temperature sensor is comprised of two internal diodes with one diode having 80 times the current density of the other. the difference in current density of the diodes yields a differential output voltage that is proportional to absolute temperature. the temperature sensor reading is converted by the adc. see figure 43 for register settings to select the temperature sensor for measurement. equation 2 shows how to convert the temperature sensor reading to degrees celsius ( ? c): temperature ( c) = [(temperature reading ( v) ? 122,400) / 420 v/ c] + 25 c (2) measure the temperature sensor with pga on, gain = 1, burn-out current sources disabled and ac-excitation mode disabled. as a result of the low package-to-pcb thermal resistance, the internal temperature closely tracks the pcb temperature. be aware that device self-heating increases the internal temperature relative to the surrounding pcb. 9.3.1.4 power-supply readback read the power-supply voltage by the appropriate input multiplexer selection. the supply voltages are divided to reduce the voltage levels to within the adc input range. the analog and digital supply readback levels are scaled by equation 3 and equation 4 , respectively: analog supply (v) = (avdd - avss) / 4 (3) digital supply (v) = dvdd / 4 (4) measure the power supply voltages with either the internal or an external reference. if using an external reference, the minimum reference voltage is 1.5 v. perform the measurement with pga enabled, gain = 1, burn- out current sources disabled and ac-excitation mode disabled. see figure 43 for register settings to measure the supply voltages. 9.3.1.5 inputs open this configuration opens all inputs. use this configuration to test the functionality of the sensor burn-out current sources, and the pga output monitors. when the inputs are open, the current sources drive the pga inputs to full scale, resulting in an pga monitor alarm and clipped conversion data. see figure 43 for register settings to open all inputs. 9.3.1.6 internal v com connection for this multiplexer configuration, all inputs are open and the pga inputs are connected to an internal v com voltage as defined: (avdd + avss) / 2. use this mode to measure the adc noise performance and offset voltage, or to short the inputs for offset calibration. see figure 43 for register settings of the internal v com connection.
28 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated feature description (continued) (1) ads1261 only. 9.3.1.7 alternate functions the adc has several alternate functions that are multiplexed with the analog inputs. the alternate functions are reference input, current source output, gpio, ac-excitation and level-shift voltage output. the functions are enabled by programming of the associated registers. the analog inputs retain measurement ability if the alternate functions are programmed. table 3 summarizes the alternate functions. table 3. analog input alternate functions analog inputs reference inputs current sources gpio/ac-excitation (1) level-shift voltage ads1260 ads1261 aincom aincom ? yes ? yes ain0 ain0 refp0 yes ? ? ain1 ain1 refn0 yes ? ? ain2 ain2 refp1 (1) yes gpio0/ acx1 ? ain3 ain3 refn1 (1) yes gpio1/ acx2 ? ain4 ain4 ? yes gpio2/acx1 ? ? ain5 ? yes gpio3/acx2 ? ? ain6 ? yes ? ? ? ain7 ? yes ? ? ? ain8 ? yes ? ? ? ain9 ? yes ? ? 9.3.2 pga the pga is a low-noise, cmos differential-input, differential-output amplifier. the pga extends the dynamic range of the adc, important when used with low level sensors. the pga provides gains of 1 through 32 and the adc provides additional gains of 2 and 4. the combined gains are 1 through 128. gain is controlled by the gain[2:0] register bits as shown in the figure 44 . in pga bypass mode, the input voltage range extends to the analog supplies. the pga is powered down in bypass mode. figure 44. pga block diagram capp 000: 1 001: 2 010: 4 011: 8 100: 16 101: 32 110: 64 111:128 + 12 pf + 12 pf v ainp v ainn capn 280 ? 280 ? gain[2:0] bits 2:0 of pga (register address = 10h) pga output monitors bypass bit 7 of pga (register address = 10h) 350 ? 350 ? 8 pf 8 pf 12 pf a1 a2 0: pga active (shown) 1: pga bypass 4.7 nf c0g adc
29 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated the pga consists of two chopper-stabilized amplifiers (a1 and a2), and a resistor network that determines the pga gain. the resistor network is precision matched, providing low drift performance. the pga integrates noise filters to reduce sensitivity to electromagnetic-interference (emi). the pga output is monitored to indicate when the operating headroom is exceeded. pins capp and capn are the pga positive and negative outputs, respectively. connect an external 4.7-nf capacitor (type c0g) as shown in figure 44 . the capacitor filters the modulator sample pulses and with the internal resistors, forms the antialias filter. place the capacitor as close as possible to the pins using short traces. avoid running clock traces or other digital traces close to these pins. the full-scale differential input voltage range of the adc is determined by the reference voltage and gain. table 4 shows the differential input voltage range verses gain for v ref = 2.5 v. (1) v ref = 2.5 v. full scale differential input voltage range is proportional to v ref . table 4. full-scale voltage range gain[2:0] bits gain full-scale differential input range (1) 000 1 2.500 v 001 2 1.250 v 010 4 0.625 v 011 8 0.312 v 100 16 0.156 v 101 32 0.078 v 110 64 0.039 v 111 128 0.0195 v as with many amplifiers, the pga has an input voltage range limitation that must not be exceeded in order to maintain linear operation. the specified input voltage range is expressed as the absolute voltage at the positive and negative inputs. as specified in equation 5 , the specified absolute input voltage depends on gain, the expected maximum differential voltage, and the minimum analog power-supply voltage. avss + 0.3 v + v in (gain ? 1) / 2 < v ainp and v ainn < avdd ? 0.3 v ? v in (gain ? 1) / 2 where ? v ainp , v ainn = absolute input voltage ? v in = maximum differential input voltage = v ainp - v ainn ? gain (for gains = 64 and 128, use gain = 32 in the calculation) ? avdd = minimum avdd voltage ? avss = maximum avss voltage (5)
30 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated the relationship of the pga input to the pga output is shown graphically in figure 45 . the pga output voltages (v outp , v outn ) depend on the respective absolute input voltage, the differential input voltage, and the pga gain. to maintain the pga within the linear operating range, the pga output voltages must not exceed either avdd ? 0.3 v or avss + 0.3 v. the diagram depicts a positive differential input voltage that results in a positive differential output voltage. figure 45. pga input/output range 9.3.2.1 pga bypass mode bypass the pga to extend the input voltage range up to the analog power supply voltages. in bypass mode, the pga is bypassed and the analog inputs are connected directly to the precharge buffers of the modulator, thereby extending the input voltage range. be aware of the increased analog input current in bypass mode. see the recommended operating conditions for the bypass-mode input voltage range specification, and see the electrical characteristics for the input current specification. 9.3.2.2 pga voltage monitor the pga has voltage monitors to provide indication when the pga is overloaded. in overload condition, the conversion data are no longer valid. if either the pga positive or negative output exceeds avdd ? 0.2 v, the high alarm bit is set (pgah_alm). similarly, if either pga positive or negative output is less than avss + 0.2 v, the low alarm bit is set (pgal_alm). the monitor alarm state is read in the status byte. the monitor alarm is read-only and automatically resets at the start of the next conversion cycle after the overload condition is cleared. the monitor diagram and threshold values are shown in figure 46 and figure 47 . figure 46. pga monitor diagram figure 47. pga monitor thresholds the pga monitors consist of fast-responding voltage comparators. comparator operation is disabled during multiplexer changes to minimize the false triggering during these input switching events. however, it is possible the monitors can detect other transient overload conditions that may occur after gain changes, sensor connection changes, and so on. avdd 0.2 v + avss + 0.2 v status byte + + + 7 6 5 4 3 2 1 0 pgah_alm pgal_alm pga pn avss + 0.2 v avss pgal_alm condition pga output avdd avdd t 0.2 v pgah_alm condition p or n p or n avss avdd 0.3 v avss + 0.3 v v outp = v ainp + v in a (gain 1) / 2 v outn = v ainn v in a (gain 1) / 2 v ainn v ainp v in = v ainp a9 ainn pga input pga output avdd
31 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.3.3 reference voltage the adc requires a reference voltage for operation. the reference voltage options are 2.5-v internal, one or two external inputs (ads1260 or ads1261, respectively) or the 5-v analog power supply. the reference voltage is selected by independent positive and negative reference multiplexers for the reference positive and reference negative voltages, respectively. the default reference is the 5-v analog power supply (avdd ? avss). figure 48 shows the block diagram of the reference multiplexer. (1) the internal reference requires a 10- f capacitor connected to pins refout and avss. (2) ads1261 only. figure 48. reference input diagram program the rmuxp[1:0] and rmuxn[1:0] bits of the ref register to select the positive and negative reference voltages, respectively. the positive reference selections are internal positive, ain0, ain2, or avdd. the negative reference input selections are internal negative, ain1, ain3, or avss. the reference low-voltage monitor is located after the reference multiplexer. see the reference monitor section for more information. 9.3.3.1 internal reference the adc incorporates a 2.5-v reference that is enabled by the refenb bit of the ref register (default = off). program the reference multiplexer bits rmuxp[1:0] and rmuxn[1:0] to 00b to select the internal reference. a 10- f capacitor is required between pins refout and avss to filter reference noise. refout is the reference output and avss is the reference return. use a star-layout connection or plane connection for the reference return, connecting close to the avss pin. when the reference is enabled, be aware of the settling time before beginning conversions. also be aware of the reference inrush current that may result in a transient droop of the avdd supply. enable the internal reference for sensor excitation current source operation. 9.3.3.2 external reference use an external reference by applying the reference voltage to the designated analog inputs. the reference inputs are differential with positive and negative inputs. program the reference multiplexer bits rmuxp[1:0] and rmuxn[1:0] to 10b or 11b to select inputs ain0/ain1 or ain2/ain3, respectively (ain2/ain3 is available only for the ads1261). for application that use multiple references, it is possible to connect the reference grounds together and use a single input pin for ground. follow the specified absolute and differential reference voltage operating conditions, as specified in the recommended operating conditions . connect a 100-nf capacitor across the reference input pins to filter noise. be aware of the reference input current if reference impedances are present. consider the error to the overall system accuracy. ain0 ain2 ain1 ain3 avss refout 10 p f internal ref avdd rmuxn[1:0] bits 1:0 of ref (register address = 06h) refenb bit 4 of ref (register address = 06h) adc v refp v refn (1) 01 10 11 00 0: internal ref off 1: internal ref on (default) (2) (2) rmuxp[1:0] bits 3:2 of ref (register address = 06h) 01 10 11 00 buf 2.5 v
32 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.3.3.3 avdd - avss reference (default) a third reference option is the 5-v analog power supply (avdd - avss). select this reference option by setting the reference multiplexer bits rmuxp[1:0] and rmuxn[1:0] to 01b. for a 6-wire load cell application that uses excitation sense lines, or for ac-excitation operation, connect the excitation sense lines to the analog input reference inputs and program the adc for external reference operation. 9.3.3.4 reference monitor the adc incorporates a reference monitor that detects an invalid reference voltage. as shown in figure 49 and figure 50 , if the reference voltage (v ref = v refp ? v refn ) is below 0.4 v, the refl_alm bit is set in the status byte. the alarm is read-only and resets at the next conversion after the low reference condition is cleared. use the reference monitor to detect a missing or failed reference voltage. to implement detection of a missing reference, use a 100-k resistor across the reference inputs. if either input is unconnected, the resistor biases the differential reference input towards 0 v so that the missing reference can be detected. figure 49. reference monitor figure 50. reference monitor threshold 9.3.4 level-shift voltage (vbias) the adc integrates a level-shift voltage that can be connected to the aincom pin by an internal switch. as shown in figure 51 , the level-shift voltage is the mid-voltage between avdd and avss. the purpose of the voltage is to shift the signal level of floating sensors to within the input range of the adc. isolated thermocouples and piezoelectric sensors are examples of sensors that are suitable for connection to the level-shift voltage. for these sensors, connect the negative lead to the aincom pin and enable the level-shift voltage. figure 51. level-shift voltage diagram the turn-on time of the level-shift voltage depends on the total external capacitance connected from the aincom pin to ground or avss. table 5 lists the level-shift voltage settling times for various load capacitance. be certain the level-shift voltage is fully settled before starting a conversion. table 5. level-shift enable time load capacitance level-shift voltage settling time 0.1 f 0.22 ms 1 f 2.2 ms 10 f 22 ms 0.4 v, typical reference low condition differential reference voltage x status byte 7 6 5 4 3 2 1 0 0.4 v refl_alm ain0 ain1 100 k + _ ref mux _ + + _ external reference aincom 100 ? v = (avdd + avss) / 2 0: off (default) 1: on vbias bit 4 of inpbias (register address = 12h)
33 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.3.5 burn-out current sources the burn-out current sources are used to detect the occurrence of sensor burn-out or break. if the sensor or sensor connection is open, the currents drive either or both positive and negative pga inputs to opposite supply voltages where the occurrence of an open sensor is detected by the pga monitors or detected by the host for out-of-range (or clipped) conversion data. figure 52 shows the burn-out currents connect at the output of the analog input multiplexer. the currents sink and source, and are configurable in pullup or pulldown mode. in pullup mode, the sourcing current connects to the positive input channel and the sinking current connects to the negative input channel. in this configuration, an open circuit pulls the inputs to positive full scale. the currents are off, 0.050 a, 0.2 a, 1 a, and 10 a. see the burn-out current source section for application information. figure 52. burn-out current sources bocs[2:0] bits 2:0 of inpbias (register address = 12h) muxp avdd 000: off 001: 0.05 ua 010: 0.2 ua 011: 1 ua 100: 10 ua pga bocsp bit 3 of inpbias (register address = 12h) 0 = pull-up mode (shown) 1 = pull-down mode ainp ainn ain0 aincom avss muxn
34 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.3.6 sensor-excitation current sources (idac1 and idac2) the adc incorporates two current sources that are used to provide excitation current to a resistive temperature device (rtd), thermistor, diode and other sensor type that require constant current biasing. the currents are programmable over the 50 a to 3000 a range and are internally multiplexed to all analog input pins. the current source multiplexer is shown in figure 53 . the imux1 and imux2 register bits connect the corresponding current source to the analog inputs. the imag1 and imag2 register bits program the corresponding current magnitude. enable the internal reference for current source operation. the current source value can be doubled or an intermediate value produced by connecting the current sources to the same analog input. take care not to exceed the current source compliance voltage range. that is, when the current source is loaded by resistance, the voltage at the pin increases and must not exceed specification; otherwise the specified current source accuracy is not met. figure 53. current source connection ain0 ain1 ain2 ain3 ain4 ain5 ain6 ain7 ain8 ain9 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 imux1[3:0] bits 3:0 of imux (register address = 0dh) 0000: off 0001: 50 a 0010: 100 a 0011: 250 a 0100: 500 a 0101: 750 a 0110: 1000 a 0111: 1500 a 1000: 2000 a 1001: 2500 a 1010: 3000 a imux2[3:0] bits 7:4 of imux (register address = 0dh) imag1[3:0] bits 3:0 of imag (register address = 0eh) imag2[3:0] bits 7:4 of imag (register address = 0eh) avdd ads1261 aincom 1111 avdd open idac1 idac2 idac1 idac2
35 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.3.7 general-purpose input/outputs (gpios) the ads1261 provides four gpio pins, gpio0 through gpio3. the gpios are digital inputs/outputs that are referenced to analog avdd and avss. the gpios are read and written by the gpio_dat bits of register mode3. the gpios are multiplexed with analog inputs ain2 to ain5. as shown in figure 54 , the gpios have a series of programming registers. bits gpio_con[3:0] connect the gpios to the associated pin (1 = connect). bits gpio_dir program the direction of the gpios; (0 = output, 1 = input). the input voltage threshold is the voltage value between avdd and avss. bits gpio_dat[3:0] are the data values for the gpios. observe that if a gpio pin is programmed as an output, the value read is the value previously written to the register data, not the actual state of the pin. the gpios also provide the ac-excitation drive signals. ac-excitation mode override the gpio register data values. see the ac-excitation mode section for details. figure 54. gpio block diagram 9.3.8 oversampling the adc operates on the principle of oversampling. oversampling is defined as the ratio of the sample rate of the modulator to that of the adc output data rate. oversampling improves adc noise by digital bandwidth limiting (low-pass filtering) of the data. the digital filter also performs data rate reduction (decimation) in order to reduce the data rate proportional with the amount of data filtering. 9.3.9 modulator the modulator is an inherently stable, fourth-order, 2 + 2 pipelined modulator. the modulator samples the analog input voltage at a high sample rate (f mod = f clk / 8) and converts the analog input to a ones-density bit- stream given by the ratio of the input signal to the reference voltage. the modulator shapes the noise of the converter to high frequency, where the noise is removed by the digital filter. ain2 gpio_con[3:0] bits 7:4 of mode2 (register address = 04h) gpio_dir[3:0] bits 3:0 of mode2 (register address = 04h) gpio_dat[3:0] bits 3:0 of mode3 (register address = 05h) ain3 ain4 ain5 + avdd + avss 2 avss avdd write read mux read select 1 0 0: gpio is output (default) 1: gpio is input 0: v gpio low (default) 1: v gpio high gpio0 gpio1 gpio2 gpio3 chop[1:0] bits 6:5 of mode1 (register address = 03h) 00: normal mode (default) 01: chop mode 10: 2-wire ac-excitation mode 11: 4-wire ac-excitation mode ac-excitation mode write 0: gpio not connected (default) 1: gpio connected
36 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.3.10 digital filter the digital filter receives the modulator output data and produces a high-resolution conversion result. the digital filter low-pass filters and decimates the modulator data (data rate reduction), yielding the final data output. by adjusting the type of filtering, tradeoffs are made between resolution, data throughput and line cycle rejection. the digital filter has two selectable modes: sin (x) / x (sinc) mode and finite impulse response (fir) mode (see figure 55 ). the sinc mode provides data rates of 2.5 sps through 40000 sps with variable sinc orders of 1 through 5. the fir filter provides simultaneous rejection of 50-hz and 60-hz frequencies with data rates 2.5 sps through 20 sps while providing single-cycle settled conversions. figure 55. digital filter block diagram 9.3.10.1 sinc filter the sinc filter is composed of two stages: a variable-decimation sinc5 filter, followed by a variable-decimation, variable-order sinc filter. the first stage filters and down-samples the modulator data to yield data rates of 40000 sps, 25600 sps, 19200 sps, and 14400 sps. these data rates bypass the second stage and as a result have a sinc5 characteristic filter response. the second stage receives data from the first stage at a fixed rate of 14400 sps. the data rate is reduced to the range 7200 sps to 2.5 sps, with programmable orders of sinc. the data rate is programmed by the dr[4:0] bits of register mode0. the filter mode is programmed by the filter[2:0] bits of register mode0 (see table 32 ). 9.3.10.1.1 sinc filter frequency response the characteristic of the sinc filter is low pass. the filter reduces noise present in the signal and noise present within the adc. changing the data rate and filter order changes the filter bandwidth. as shown in figure 56 and figure 57 , the first-stage sinc5 filter has frequency response nulls occurring at n f data , where n = 1, 2, 3 and so on. at the null frequencies, the filter has zero gain. data rates of 25600 sps and 19200 sps have similar frequency response. figure 56. frequency response (40000 sps) figure 57. frequency response (14400 sps) frequency (khz) amplitude (db) 0 10 20 30 40 50 60 70 80 90 100 110 120 -160 -140 -120 -100 -80 -60 -40 -20 0 d002 sinc 5 filter sinc n filter modulator fir averager fir filter section filter mux sinc filter section to offset/gain calibration 40000 sps to 14400 sps 7200 sps to 2.5 sps 20 sps 10 sps 5 sps 2.5 sps f clk / 8 ( = data rate reduction) frequency (khz) amplitude (db) 0 10 20 30 40 50 60 70 80 90 100 110 120 -160 -140 -120 -100 -80 -60 -40 -20 0 d101
37 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated the second stage superimposes frequency response nulls to the nulls of the first stage 14400 sps output. the first of the superimposed response nulls occurs at the data rate, followed by nulls occurring at multiples of the data rate. figure 58 illustrates the frequency response for various orders of sinc at data rate of 2400 sps. this data rate has five nulls between the larger nulls at multiples of 14400 hz. this frequency response is similar to that of data rates 2.5 sps to 7200 sps. figure 59 shows the frequency response nulls for 10 sps. figure 58. sinc frequency response (2400 sps) figure 59. sinc frequency response (10 sps) figure 60 and figure 61 show the frequency response of data rates 50 sps and 60 sps, respectively. increase the attenuation at 50 hz or 60 hz and harmonics by increasing the order of the sinc filter, as shown in the figures. figure 60. sinc frequency response (50 sps) figure 61. sinc frequency response (60 sps) figure 62 and figure 63 show the detailed frequency response at 50 sps and 60 sps, respectively. figure 62. detail sinc frequency response (50 sps) figure 63. detail sinc frequency response (60 sps) frequency (hz) amplitude (db) 45 46 47 48 49 50 51 52 53 54 55 -160 -140 -120 -100 -80 -60 -40 -20 0 d009 sinc1 sinc2 sinc3 sinc4 frequency (hz) amplitude (db) 0 50 100 150 200 250 300 350 400 450 500 550 600 -160 -140 -120 -100 -80 -60 -40 -20 0 d005 sinc1 sinc2 sinc3 sinc4 frequency (hz) ampliude (db) 55 56 57 58 59 60 61 62 63 64 65 -160 -140 -120 -100 -80 -60 -40 -20 0 d010 sinc1 sinc2 sinc3 sinc4 frequency (hz) amplitude (db) 0 10 20 30 40 50 60 70 80 90 100 110 120 -160 -140 -120 -100 -80 -60 -40 -20 0 d004 sinc1 sinc2 sinc3 sinc4 frequency (khz) amplitude (db) 0 5 10 15 20 25 30 35 40 45 -160 -140 -120 -100 -80 -60 -40 -20 0 d003 sinc1 sinc2 sinc3 sinc4 frequency (hz) amplitude (db) 0 60 120 180 240 300 360 420 480 540 600 -160 -140 -120 -100 -80 -60 -40 -20 0 d006 sinc1 sinc2 sinc3 sinc4
38 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.3.10.2 fir filter the finite impulse response (fir) filter is a coefficient based filter architecture that provides an overall low-pass filter response. the filter provides simultaneous attenuation of 50 hz and 60 hz and harmonics at data rates of 20 sps to 2.5 sps. the conversion latency time of the fir filter data rates are single-cycle. as shown in figure 55 , the fir filter receives pre-filtered data from the sinc filter. the fir filter decimates the data to yield the output data rates of 20 sps. a variable averager (sinc1) provides data rates of 10 sps, 5 sps, and 2.5 sps. table 6 lists the bandwidth of the data rates in fir filter mode. 9.3.10.2.1 fir filter frequency response figure 64 and figure 65 show the fir filter frequency attenuates 50 hz and 60 hz by a series of response nulls placed close to these frequencies. the response nulls are repeated at harmonics of 50 hz and 60 hz. figure 64. fir frequency response (20 sps) figure 65. fir frequency response detail (20 sps) figure 66 is the fir filter response at 10 sps. as a result of the variable averager, new frequency nulls are superimposed. the first null appears at the date rate. additional nulls occur at frequencies folded around multiples of 20 hz. figure 66. fir frequency response (10 sps) frequency (hz) amplitude (db) 0 30 60 90 120 150 180 210 240 270 300 -160 -140 -120 -100 -80 -60 -40 -20 0 d013 frequency (hz) amplitude (db) 40 45 50 55 60 65 70 -160 -140 -120 -100 -80 -60 -40 -20 0 d012 frequency (hz) amplitude (db) 0 30 60 90 120 150 180 210 240 270 300 -160 -140 -120 -100 -80 -60 -40 -20 0 d011
39 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.3.10.3 filter bandwidth the bandwidth of the filter depends on the data rate and the filter mode. be aware that the bandwidth of the entire system is the combined response of the filter, the antialias filter and external filters. table 6 lists the bandwidth versus data rate and filter mode. table 6 also lists the filter modes available for each data rate. table 6. filter bandwidth data rate (sps) -3-db bandwidth (hz) fir sinc1 sinc2 sinc3 sinc4 sinc5 2.5 1.2 1.10 0.80 0.65 0.58 ? 5 2.4 2.23 1.60 1.33 1.15 ? 10 4.7 4.43 3.20 2.62 2.28 ? 16.6 ? 7.38 5.33 4.37 3.80 ? 20 13 8.85 6.38 5.25 4.63 ? 50 ? 22.1 16.0 13.1 11.4 ? 60 ? 26.6 19.1 15.7 13.7 ? 100 ? 44.3 31.9 26.2 22.8 ? 400 ? 177 128 105 91.0 ? 1200 ? 525 381 314 273 ? 2400 ? 1015 751 623 544 ? 4800 ? 1798 1421 1214 1077 ? 7200 ? 2310 1972 1750 1590 ? 14400 ? ? ? ? ? 2940 19200 ? ? ? ? ? 3920 25600 ? ? ? ? ? 5227 40000 ? ? ? ? ? 8167
40 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.3.10.4 50-hz and 60-hz normal mode rejection to reduce 50-hz and 60-hz noise interference, configure the conversion period to reject the noise at 50 hz and 60 hz. 50-hz and 60-hz noise rejection depends on the filter type. table 7 summarizes the 50-hz and 60-hz noise rejection versus data rate and filter type. the table values are based on 2% and 6% tolerance of noise frequency to adc clock frequency. for the sinc filter mode, noise rejection is increased by increasing the order of the filter. common mode noise is also rejected at these frequencies. table 7. 50-hz and 60-hz normal mode rejection data rate (sps) filter type digital filter response (db) 50 hz 2% 60 hz 2% 50 hz 6% 60 hz 6% 2.5 fir ? 113 ? 99 ? 88 ? 80 2.5 sinc1 ? 36 ? 37 ? 40 ? 37 2.5 sinc2 ? 72 ? 74 ? 80 ? 74 2.5 sinc3 ? 108 ? 111 ? 120 ? 111 2.5 sinc4 ? 144 ? 148 ? 160 ? 148 5 fir ? 111 ? 95 ? 77 ? 76 5 sinc1 ? 34 ? 34 ? 30 ? 30 5 sinc2 ? 68 ? 68 ? 60 ? 60 5 sinc3 ? 102 ? 102 ? 90 ? 90 5 sinc4 ? 136 ? 136 ? 120 ? 120 10 fir ? 111 ? 94 ? 73 ? 68 10 sinc1 ? 34 ? 34 ? 25 ? 25 10 sinc2 ? 68 ? 68 ? 50 ? 50 10 sinc3 ? 102 ? 102 ? 75 ? 75 10 sinc4 ? 136 ? 136 ? 100 ? 100 16.6 sinc1 ? 34 ? 21 ? 24 ? 21 16.6 sinc2 ? 68 ? 42 ? 48 ? 42 16.6 sinc3 ? 102 ? 63 ? 72 ? 63 16.6 sinc4 ? 136 ? 84 ? 96 ? 84 20 fir ? 95 ? 94 ? 66 ? 66 20 sinc1 ? 18 ? 34 ? 18 ? 24 20 sinc2 ? 36 ? 68 ? 36 ? 48 20 sinc3 ? 54 ? 102 ? 54 ? 72 20 sinc4 ? 72 ? 136 ? 72 ? 96 50 sinc1 ? 34 ? 15 ? 24 ? 15 50 sinc2 ? 68 ? 30 ? 48 ? 30 50 sinc3 ? 102 ? 45 ? 72 ? 45 50 sinc4 ? 136 ? 60 ? 96 ? 60 60 sinc1 ? 13 ? 34 ? 12 ? 24 60 sinc2 ? 27 ? 68 ? 24 ? 48 60 sinc3 ? 40 ? 102 ? 36 ? 72 60 sinc4 ? 53 ? 136 ? 48 ? 96
41 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.4 device functional modes 9.4.1 conversion control conversions are controlled by either the start pin or by the start command. if using commands to control conversions, keep the start pin low to avoid contentions between pin and commands. commands take affect on the 16th falling sclk edge (crc mode disabled) or on the 32nd falling sclk edge (crc mode enabled). see figure 4 for conversion-control timing details. the adc provides two conversion modes: continuous and pulse. the continuous-conversion mode performs conversions indefinitely until stopped by the user. pulse-conversion mode performs one conversion and then stops. the conversion mode is programmed by the convrt bit (bit 4 of register mode0). 9.4.1.1 continuous-conversion mode this conversion mode performs continuous conversions until stopped by the user. to start conversions, take the start pin high or send the start command. drdy is driven high at the time the conversion is initiated. drdy is driven low when the conversion data are ready. conversion data are available to read at that time. conversions are stopped by taking the start pin low or by sending the stop command. when conversions are stopped, the conversion in progress runs to completion. to restart a conversion that is in progress, toggle the start pin low-then-high or send a new start command. 9.4.1.2 pulse-conversion mode in pulse-conversion mode, the adc performs one conversion when start is taken high or when the start command is sent. when the conversion completes, further conversions stop. the drdy output is driven high to indicate the conversion is in progress, and is driven low when the conversion data are ready. conversion data are available to read at that time. to restart a conversion in progress, toggle the start pin low-then-high or send a new start command. driving start low or sending the stop command does not interrupt the current conversion. 9.4.1.3 conversion latency the digital filter averages data from the modulator in order to produce the conversion result. the stages of the digital filter must have settled data in order to provide fully-settled output data. the order and the decimation ratio of the digital filter determine the amount of data averaged, and in turn, affect the latency of the conversion data. the fir and sinc1 filter modes are zero latency because the adc provides the conversion result in one conversion cycle. latency time is an important consideration for the data throughput rate in multiplexed applications. table 8 lists the conversion latency values of the adc. conversion latency is defined as the time from the start of the first conversion, by taking the start pin high or sending the start command, to the time when the conversion data are ready. if the input signal is settled, then the adc provides fully settled data under this condition. the conversion latency values listed in the table are with the start-conversion delay parameter = 50 s, and include the overhead time needed to process the data. after the first conversion completes (in continuous conversion mode), the period of the following conversions are equal to 1/f data . the first conversion latency in chop and ac-excitation modes are twice the values listed in the table. also when operating in these modes, the period of the following conversions are equal to the values listed in the table.
42 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated device functional modes (continued) (1) chop mode off, conversion-start delay = 50 s (delay[3:0] = 0001) table 8. conversion latency data rate (sps) conversion latency - t (stdr) (1) (ms) fir sinc1 sinc2 sinc3 sinc4 sinc5 2.5 402.2 400.4 800.4 1,200 1,600 ? 5 202.2 200.4 400.4 600.4 800.4 ? 10 102.2 100.4 200.4 300.4 400.4 ? 16.6 ? 60.43 120.4 180.4 240.4 ? 20 52.23 50.43 100.4 150.4 200.4 ? 50 ? 20.43 40.43 60.43 80.43 ? 60 ? 17.09 33.76 50.43 67.09 ? 100 ? 10.43 20.43 30.43 40.43 ? 400 ? 2.925 5.425 7.925 10.43 ? 1200 ? 1.258 2.091 2.925 3.758 ? 2400 ? 0.841 1.258 1.675 2.091 ? 4800 ? 0.633 0.841 1.050 1.258 ? 7200 ? 0.564 0.702 0.841 0.980 ? 14400 ? ? ? ? ? 0.423 19200 ? ? ? ? ? 0.336 25600 ? ? ? ? ? 0.271 40000 ? ? ? ? ? 0.179 if the input signal changes while free-running conversions, the conversion data are a mix of old and new data, as shown in figure 67 . after an input change, the number of conversion periods required for fully settled data are determined by dividing the conversion latency by the period of the data rate, plus add one conversion period to the result. in chop mode and ac-excitation mode, use twice the latency values listed in the table. figure 67. input change during conversions 9.4.1.4 start-conversion delay some applications may require a delay at the start of a conversion in order to allow settling time for the pga output antialias filter or to allow time after input and configuration changes. the adc provides a user programmable delay time that delays the start of a new conversion. the default value is 50 s. this allows for settling of the antialiasing filter. use additional delay time as needed to provide settling time for external components. the delay time increases the conversion latency values listed in table 8 . as an alternative to the programmable start-conversion delay, manually delay the start of conversion after input and configuration changes. start-conversion delay is an important consideration for operation in ac-excitation mode. in this mode, the reference inputs to the bridge, and therefore, the bridge output signals are reversed for each conversion as a result, time delay is required to allow for settling of external filter components after reversal. as a general guideline, set the start-conversion delay parameter to a minimum of 15 times the r-c time constant of the signal input and reference input filters. drdy pin v in = v ainp - v ainn old v in new v in old data mix of old data and new data fully settled new data
43 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.4.2 chop mode the pga and modulator are chopper-stabilized at high frequency in order to reduce offset voltage, offset voltage drift and 1/f noise. the offset and noise artifacts are modulated to high frequency and are removed by the digital filter. although chopper stabilization is designed to remove all offset, a small offset voltage may remain. the optional global chop mode removes the remaining offset errors, providing exceptional offset voltage drift performance. chop mode alternates the signal polarity of consecutive conversions. the adc subtracts consecutive, alternate- phase conversions to yield the final conversion data. the result of subtraction removes the offset. figure 68. adc chop mode as shown in figure 68 , the internal chop switch reverses the signal after the input multiplexer. v ofs models the internal offset voltage. the operational sequence of chop mode is as follows: conversion c1 : v ainp ? v ainn ? v ofs first conversion withheld after start conversion c2 : v ainn ? v ainp ? v ofs output 1 = (c1 ? c2) / 2 = v ainp ? v ainn conversion c3: v ainp ? v ainn ? v ofs output 2 = (c3 ? c2) / 2 = v ainp ? v ainn the sequence repeats for all conversions. because of the internal mathematical operations, the chop mode data rate is reduced. the chop mode data rate is proportional to the order of the sinc filter. referring to table 8 , the new data rate is equal to 1 / latency values and the first conversion latency is 2 latency values. because of the two-point data averaging arising from the mathematical operations, noise is reduced by 2. for chop mode, divide the noise data values shown in table 1 by 2 to derive the new noise performance data. the null frequencies of the digital filter are not changed in chop-mode operation. however, new null frequencies appear at multiples of f data / 2. 9.4.3 ac-excitation mode resistive bridge sensors are excited by dc or ac voltages; for dc or ac currents. dc voltage excitation is the most common type of excitation. ac excitation reverses the polarity of the voltage by the use of external switching components. similar in concept to chop mode, the result of the voltage reversal removes offset voltage in the connections leading from the bridge to the adc inputs. this removal includes the offset voltage of the adc itself. the ads1261 provides the signals necessary to drive the external switching components in order to reverse the bridge voltage. the timing of the drive signals is synchronized to the adc conversion phase. during one conversion phase, the voltage polarity is normal. for the alternate conversion phase, the voltage polarity is reversed. the adc compensates the reversed polarity conversion by internal reversal of the reference voltage. the adc subtracts the data corresponding to the normal and reverse phases in order to remove offset voltage from the input. the adc output drive signals do not overlap in order to avoid bridge cross-conduction that can otherwise occur during excitation voltage reversal. the switch rate of the ac-excitation drive signals are at the data rate to avoid unnecessary fast switching. see figure 7 for output drive timing. v ofs adc pga adc digital filter + - chop control conversion output input mux chop switch chop[1:0] bits 6:5 of mode1 (register address = 03h) v ainp v ainn 00: normal mode 01: chop mode 10: 2-wire ac excitation mode 11: 4-wire ac excitation mode ain0 aincom offset cal full-scale cal
44 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated table 9 shows the ac-excitation drive signals and the associated gpio pins. program the ac-excitation mode using the chop[1:0] bits in register mode1. ac excitation can be programmed for two-wire or four-wire drive mode. for two-wire operation, two drive signals are provided on the gpios. if needed, use two external inverters to derive four signals to drive discrete transistors. the gpio drive levels are referred to the 5-v analog supply. be aware that the ac-excitation mode changes the nominal data rate, depending on the order of the sinc filter. see the chop mode section for details of the effective data rate. table 9. ac-excitation drive pins device pin gpio 2-wire mode (chop[1:0] = 10) 4-wire mode (chop[1:0] = 11) ain2 gpio0 acx1 acx1 ain3 gpio1 acx2 acx2 ain4 gpio2 ? acx1 ain5 gpio3 ? acx2 9.4.4 adc clock mode operate the adc with an external clock or with the internal oscillator. the clock frequency is 7.3728 mhz, except for f data = 40000 sps then f clk = 10.24 mhz (internal or external). for external clock operation, apply the clock signal to clkin. for internal-clock operation, connect clkin to dgnd. the internal oscillator begins operation immediately at power-up. the adc automatically selects the clock mode of operation. read the clock mode bit in the status register to determine the clock mode. 9.4.5 power-down mode the adc has two power-down modes: hardware and software. in both power-down modes, the digital outputs remain driven. the digital inputs must be maintained at v ih or v il levels (do not float the digital inputs). the internal low-dropout regulator remains on, drawing 25 a (typical) from dvdd. 9.4.5.1 hardware power-down take the pwdn pin low to engage hardware power-down mode. except for the internal ldo, all adc functions are disabled. to exit hardware power-down mode (wake-up) take the pwdn pin high. the register values are not reset at wake-up. the internal reference is shut down in this mode; therefore, be sure to accommodate the start-up time of the internal reference before starting conversions. 9.4.5.2 software power-down set the pwdn bit (bit 7 of register mode3) to engage software power-down mode. similar to the operation of hardware power-down mode, software mode powers down the internal functions except the serial interface remains powered, and the internal reference bias is unchanged (on or off). exit the software power-down mode by clearing the pwdn bit. the register values are not reset. 9.4.6 reset the adc is reset in three ways: at power-on, by the reset pin, and by the reset command. when reset, the serial interface, conversion-control logic, digital filter, and register values are reset. the reset bit of the status byte is set to indicate a device reset has occurred by any of the three reset methods. clear the bit to detect the next device reset. if the start pin is high after reset, the adc begins conversions. 9.4.6.1 power-on reset at power-on, after the supply voltages cross the reset-voltage thresholds, the adc is reset and 2 16 f clk cycles later the adc is ready for communication. until this time, drdy is held low. drdy is driven high to indicate when the adc is ready for communication. if the start pin is high, the conversion cycle starts 512 / f clk cycle after drdy asserts high. figure 5 shows the power-on reset behavior. 9.4.6.2 reset by pin reset the adc by taking the reset pin low and then returning the pin high. after reset, the conversion starts 512 / f clk cycles later. see figure 6 for reset timing.
45 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.4.6.3 reset by command reset the adc by the reset command. toggle cs high to make sure the serial interface resets before sending the command. for applications that tie cs low, see the serial interface auto-reset section for information on how to reset the serial interface. after reset, the conversion starts 512 / f clk cycles later. see figure 6 for timing details. 9.4.7 calibration the adc incorporates calibration registers and associated commands to calibrate offset and full-scale errors. calibrate by using calibration commands, or calibrate by writing to the calibration registers directly (user calibration). to calibrate by command, send the offset or full-scale calibration commands. to user calibrate, write values to the calibration registers based on calculations of the conversion data. perform offset calibration before full-scale calibration. 9.4.7.1 offset and full-scale calibration use the offset and full-scale (gain) registers to correct offset or full-scale errors, respectively. as shown in figure 69 , the offset calibration register is subtracted from the output data before multiplication by the full-scale register, which is divided by 400000h. after the calibration operation, the final output data are clipped to 24 bits. figure 69. calibration block diagram equation 6 shows the internal calibration. final output data = (filter output - ofcal[2:0]) fscal[2:0] / 400000h (6) 9.4.7.1.1 offset calibration registers the offset calibration word is 24 bits, consisting of three 8-bit registers, as listed in table 10 . the offset value is subtracted from the conversion result. the offset value is in two's complement format with a maximum positive value equal to 7fffffh, and a maximum negative value equal to 800000h. a register value equal to 000000h has no offset correction. although the offset calibration register provides a wide range of possible offset values, the input signal after calibration cannot exceed 106% of the pre-calibrated range; otherwise, the adc is overranged. table 11 lists example values of the offset register. table 10. offset calibration registers register byte order address bit order ofcal0 lsb 07h b7 b6 b5 b4 b3 b2 b1 b0 (lsb) ofcal1 mid 08h b15 b14 b13 b12 b11 b10 b9 b8 ofcal2 msb 09h b23 (msb) b22 b21 b20 b19 b18 b17 b16 (1) output value with no offset error table 11. offset calibration register values ofcal[2:0] register value ideal output value (1) 000001h ffffffh 000000h 000000h ffffffh 000001h + ofcal[2:0] registers (register addresses = 07h, 08h, 09h) v ainp 1/400000h fscal[2:0] registers (register addresses = 0ah, 0bh, 0ch) - digital filter adc adc output data clipped to 24 bits final output v ainn
46 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.4.7.1.2 full-scale calibration registers the full-scale calibration word is 24 bits consisting of three 8-bit registers, as listed in table 12 . the full-scale calibration value is in straight-binary format, normalized to a unity-gain factor at a value of 400000h. table 13 lists register values for selected gain factors. gain errors greater than unity are corrected by using full-scale values less than 400000h. although the full-scale register provides a wide range of possible values, the input signal after calibration must not exceed 106% of the precalibrated input range; otherwise, the adc is overranged. table 12. full-scale calibration registers register byte order address bit order fscal0 lsb 0ah b7 b6 b5 b4 b3 b2 b1 b0 (lsb) fscal1 mid 0bh b15 b14 b13 b12 b11 b10 b9 b8 fscal2 msb 0ch b23 (msb) b22 b21 b20 b19 b18 b17 b16 table 13. full-scale calibration register values fscal[2:0] register value gain factor 433333h 1.05 400000h 1.00 3ccccch 0.95 9.4.7.2 offset self-calibration (sfocal) the offset self-calibration command corrects offset errors internal to the adc. when the offset self-calibration command is sent, the adc disconnects the external inputs, shorts the inputs to the pga, and then averages 16 conversion results to compute the calibration value. averaging the data reduces conversion noise to improve calibration accuracy. when calibration is complete, the adc restores the user input and performs one conversion using the new calibration value. 9.4.7.3 offset system-calibration (syocal) the offset system-calibration command corrects system offset errors. for this type of calibration, the user shorts the inputs to either the adc or to the system. when the command is sent, the adc averages 16 conversion results to compute the calibration value. averaging the data reduces conversion noise to improve calibration accuracy. when calibration is complete, the adc performs one conversion using the new calibration value. 9.4.7.4 full-scale calibration (gancal) the full-scale calibration command corrects gain error. to calibrate, apply a positive full-scale calibration voltage to the adc, wait for the signal to settle, and then send the calibration command. the adc averages 16 conversion results to compute the calibration value. averaging the data reduces conversion noise to improve calibration accuracy. the adc computes the full-scale calibration value so that the calibration voltage is scaled to positive full scale output code. when calibration is complete, the adc performs one new conversion using the new calibration value.
47 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated (1) nominal clock frequency. chop and ac-excitation modes disabled. 9.4.7.5 calibration command procedure use the following procedure to calibrate using commands. the register-lock mode must be unlock for all calibration commands. after power-on, make sure the reference voltage has stabilized before calibrating. perform offset calibration before full-scale calibration. 1. configure the adc as required. 2. apply the appropriate calibration signal (zero or full-scale) 3. take the start pin high or send the start command to start conversions. drdy is driven high. 4. before the conversion cycle completes, send the calibration command. keep cs low otherwise the command is cancelled. send no other commands during the calibration period. 5. calibration time depends on the data rate and digital filter mode. see table 14 . drdy asserts low when calibration is complete. the offset or full-scale calibration registers are updated with new values. at calibration completion, new conversion data are ready using the new calibration value. table 14. calibration time (ms) data rate (sps) filter mode (1) fir sinc1 sinc2 sinc3 sinc4 sinc5 2.5 6805 6801 7601 8401 9201 ? 5 3405 3401 3801 4201 4601 ? 10 1705 1701 1901 2101 2301 ? 16.6 ? 1021 1141 1261 1381 ? 20 854.5 850.9 951.0 1051 1151 ? 50 ? 340.9 380.9 420.9 460.9 ? 60 ? 284.2 317.5 350.9 384.2 ? 100 ? 170.9 190.9 210.9 230.9 ? 400 ? 43.36 48.36 53.36 58.36 ? 1200 ? 15.02 16.69 18.36 20.02 ? 2400 ? 7.938 8.772 9.605 10.44 ? 4800 ? 4.397 4.813 5.230 5.647 ? 7200 ? 3.216 3.494 3.772 4.050 ? 14400 ? ? ? ? ? 1.892 19200 ? ? ? ? ? 1.458 25600 ? ? ? ? ? 1.133 40000 ? ? ? ? ? 0.738 9.4.7.6 user calibration procedure to user calibrate, apply the calibration voltage, acquire conversion data, and compute the calibration value. the computed value is written to the corresponding calibration registers. before starting calibration, preset the offset and full-scale registers to 000000h and 400000h, respectively. to offset calibrate, short the adc inputs (or inputs to the system) and average n number of the conversion results. averaging conversion data reduces noise to improve calibration accuracy. write the averaged value of the conversion data to the offset registers. to gain calibrate using a full scale calibration voltage, temporarily reduce the full scale register 95% to avoid output clipped codes (set fscal[2:0] to 3ccccch). acquire n number of conversions and average the conversions to reduce noise to improve calibration accuracy. compute the full-scale calibration value as shown in equation 7 : full-scale calibration value = expected code / actual code 400000h where ? expected code = 799998h using full scale calibration signal and 95% scale factor (7)
48 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.5 programming 9.5.1 serial interface the serial interface is spi-compatible and is used to read conversion data, configure registers, and control the adc. the serial interface consists of four control lines: cs, sclk, din, and dout/ drdy. most microcontroller spi peripherals can operate with the adc. the interface operates in spi mode 1, where cpol = 0 and cpha = 1. in spi mode 1, sclk idles low and data are updated or changed on sclk rising edges; data are latched or read on sclk falling edges. timing details of the spi protocol are found in figure 1 and figure 2 . 9.5.1.1 chip select ( cs) cs is an active-low input that selects the serial interface for communication. cs must be low during the entire data transaction. when cs is taken high, the serial interface resets, sclk input activity is ignored (blocking commands), and dout/ drdy enters the high-impedance state. the operation of drdy is not effected by cs. if the adc is a single device connected to the serial bus, cs can be tied low in order to reduce the serial interface to three lines. 9.5.1.2 serial clock (sclk) sclk is the serial clock input that shifts data into and out of the adc. output data are updated on the rising edge of sclk and input data are latched on the falling edge of sclk. return sclk low after the data operation is completed. sclk is a schmidt-triggered input designed to improve noise immunity. even though sclk is noise resistant, keep sclk as noise-free as possible to avoid unintentional sclk transitions. avoid ringing and overshoot on the sclk input. place a series termination resistor close to the sclk drive pin to reduce ringing. 9.5.1.3 data input (din) din is the serial data input to the adc. din is used to input commands and register data to the adc. data are latched on the falling edge of sclk. 9.5.1.4 data output/data ready (dout/ drdy) the dout/ drdy pin is a dual-function output. the functions of this pin are data output and data ready. the functionality changes automatically based on whether a read data operation is in progress. during a read data operation, the functionality is data output. after the read operation is complete, the functionality changes to data ready. in data output mode, data are updated on the sclk rising edge, therefore the host latches the data on the falling edge of sclk. in data-ready mode, the pin functions the same as drdy (if cs is low) by asserting low when data are ready. therefore, monitor either dout/ drdy or drdy to determine when data are ready. when cs is high, the dout/ drdy pin is in the high-impedance mode (tri-state). 9.5.1.5 serial interface auto-reset the serial interface is reset by taking cs high. applications that tie cs low do not have the ability to reset the serial interface by cs. if a false sclk occurs (for example, caused by a noise pulse or clocking glitch), the serial interface may inadvertently advance one or more bit positions, resulting in loss of synchronization to the host. if loss of synchronization occurs, the adc interface does not respond correctly until the interface is reset. for applications that tie cs low, the serial interface auto-reset feature recovers the interface in the event that an unintentional sclk glitch occurs. when the first sclk low-to-high transition occurs (either caused by a glitch or by normal sclk activity), seven sclk transitions must occur within 65536 f clk cycles (8.9 ms) to complete the byte transaction, otherwise the serial interface resets. after reset, the interface is ready to begin the next byte transaction. if the byte transaction is completed within the 65536 f clk cycles, the serial interface does not reset. the cycle of sclk detection re-starts at the next rising edge of sclk. the serial interface is reset by holding sclk low for a minimum 65536 f clk cycles. the auto-reset function is enabled by the spitim bit (default is off). see figure 3 for timing details.
49 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated programming (continued) 9.5.2 data ready ( drdy) drdy is an output that asserts low when conversion data are ready. after power-up, drdy also indicates when the adc is ready for communication. the operation of drdy depends on the conversion mode (continuous or pulse) and whether the conversion data are retrieved or not. figure 70 shows drdy operation with and without data retrieval in the two modes of conversion. figure 70. drdy operation 9.5.2.1 drdy in continuous-conversion mode in continuous-conversion mode, drdy is driven high when conversions are started and is driven low when conversion data are ready. during data readback, drdy returns high at the end of the read operation. if the conversion data are not read, drdy pulses high 16 f clk cycles prior to the next falling edge. to read conversion data before the next conversion is ready, send the complete read-data command 16 f clk cycles before the next drdy falling edge. if the readback command is sent less than 16 f clk cycles before the drdy falling edge, either old or new conversion data are provided, depending on the timing of when the command is sent. in the case that old conversion data are provided, drdy driven low is delayed until after the read data operation is completed. in this case, the drdy bit of the status byte is cleared to indicate the same data have been read. if new conversion data are provided, drdy transitions low at the normal period of the data rate. in this case, the drdy bit of the status byte is set to indicate that new data have been read. to make sure new data are read back, wait until drdy asserts low before starting the data read operation. 9.5.2.2 drdy in pulse-conversion mode drdy is driven high at conversion start and is driven low when the conversion data are ready. during the data read operation drdy remains low until a new conversion is started. 9.5.2.3 data ready by software polling use software polling of data ready in lieu of hardware polling of drdy or dout/ drdy. to software poll, read the status register and poll the drdy bit. in order to not skip conversion data in continuous conversion mode, poll the bit at least as often as the period of the data rate. if the drdy bit is set, then conversion data are new since the previous data read operation. if the bit is cleared, conversion data are not new since the previous data read operation. in this case, the previous conversion data are returned. 9.5.3 conversion data conversion data are read by the rdata command. to read data, take cs low and issue the read data command. the data field response consists of the optional status byte, three data bytes, and the optional crc byte. the crc is computed over the combination of status byte and conversion data bytes. see the rdata command for details to read conversion data. (continuous-conversion mode) start (continuous-conversion mode) (pulse-conversion mode) command start start stop drdy - with data retrieval drdy w/o data retrieval drdy w or w/o data retreival stop
50 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated programming (continued) 9.5.3.1 status byte (status) the status byte contains information on the operating state of the adc. the status byte is included with the conversion data by enabling bit statenb of register mode3. optionally, read the status register directly to read status information without the need to read conversion data. see figure 76 for details. 9.5.3.2 conversion data format the conversion data are 24 bits, in two's-complement format to represent positive and negative values. the data output begins with the most significant bit (sign bit) first. the data are scaled so that v in = 0 v results in an uncalibrated code value of 000000h; positive full scale equals 7fffffh and negative full scale equals 800000h; see table 15 for the uncalibrated code values. the data are clipped to 7fffffh (positive full scale) and 800000h (negative full scale) during positive and negative signal overdrive, respectively. (1) ideal (calibrated) conversion data. table 15. adc conversion data codes description input signal (v) 24-bit conversion data (1) positive full scale v ref / gain (2 23 - 1) / 2 23 7fffffh 1 lsb v ref / (gain 2 23 ) 000001h zero scale 0 000000h -1 lsb ? v ref / (gain 2 23 ) ffffffh negative full scale ? v ref / gain 800000h 9.5.4 crc cyclic redundancy check (crc) is an error checking code that detects communication errors to and from the host. crc is the division remainder of the data payload bytes by a fixed polynomial. the data payload is 1, 2, 3 or 4 bytes depending on the data operation. the crc mode is optional and is enabled by the crcenb bit. see table 35 to program the crc mode. the user computes the crc corresponding to the two command bytes and appends the crc to the command string (3rd byte). a 4th, zero-value byte completes the command field. the adc repeats the crc calculation and compares the calculation to the received crc. if the user and repeated crc values match, the command executes and the adc responds by transmitting the repeated crc during the 4th byte of the command. if the operation is conversion data or register data read, the adc responds with a 2nd crc that is computed over the requested data payload bytes. the response data payload is 1, 3, or 4 bytes depending on the data operation. if the user and repeated crc values do not match, the command does not execute and the adc responds with an inverted crc for the actual received command bytes. the inverted crc is intended to signal the host of the failed operation. the user terminates transmission of the command bytes to match the action of adc termination. the crcerr bit is set in the status register when a crc error is detected. the adc is ready to accept the next command after a crc error occurs at the end of the 4th byte. the crc data byte is the 8-bit remainder of the bitwise exclusive-or (xor) operation of the argument by a crc polynomial. the crc polynomial is based on the crc-8-atm (hec): x 8 + x 2 + x 0 + 1. the nine binary polynomial coefficients are: 100000111. the crc calculation is preset with "1" data values. the crc mnemonics apply to the following command sections. ? crc-2: input crc of command bytes 1 and 2. except for wreg command, the value of byte 2 is arbitrary ? out crc-1: output crc of one register data byte ? out crc-2: output crc of two command bytes, inverted value if input crc error detected ? out crc-3: output crc of three conversion data bytes ? out crc-4: output crc of three conversion data bytes plus status byte ? echo byte 1: echo of received input byte 1 ? echo byte 2: echo of received input byte 2
51 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated (1) rrh = 5-bit register address. 9.5.5 commands commands read conversion data, control the adc, and read and write register data. see table 16 for the list of commands. send only the commands that are listed in table 16 . the adc executes commands at completion of the 2nd byte (no crc verification) or at completion of the 4th byte (with crc verification). follow the two byte or four byte format according to the crc mode. except for register write commands, the value of the second command byte is arbitrary but the value is included in the crc calculation (total of two-byte crc). if a crc error is detected, the adc does not execute the command. taking cs high before the command is completed results in termination of the command. when cs is taken low, the communication frame is reset to start a new command. table 16. command byte summary mnemonic description byte 1 byte 2 byte 3 (crc mode only) byte 4 (crc mode only) control commands nop no operation 00h arbitrary crc-2 00h reset reset 06h arbitrary crc-2 00h start start conversion 08h arbitrary crc-2 00h stop stop conversion 0ah arbitrary crc-2 00h read data command rdata read conversion data 12h arbitrary crc-2 00h calibration commands syocal system offset calibration 16h arbitrary crc-2 00h gancal gain calibration 17h arbitrary crc-2 00h sfocal self offset calibration 19h arbitrary crc-2 00h register commands rreg read register data 20h + rrh (1) arbitrary crc-2 00h wreg write register data 40h + rrh (1) register data crc-2 00h protection commands lock register lock f2h arbitrary crc-2 00h unlock register unlock f5h arbitrary crc-2 00h 9.5.5.1 nop command this command is no operation. use the nop command to validate the crc response byte and error detection without affecting normal operation. table 17 shows the nop command byte sequence. table 17. nop command direction byte 1 byte 2 byte 3 byte 4 no crc mode din 00h arbitrary dout/ drdy ffh echo byte 1 crc mode din 00h arbitrary crc-2 00h dout/ drdy ffh echo byte 1 echo byte 2 out crc-2
52 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.5.5.2 reset command the reset command resets adc operation and resets the registers to default values. see the reset by command section for details. table 18 shows the reset command byte sequence. table 18. reset command direction byte 1 byte 2 byte 3 byte 4 no crc mode din 06h arbitrary dout/ drdy ffh echo byte 1 crc mode din 06h arbitrary crc-2 00h dout/ drdy ffh echo byte 1 echo byte 2 out crc-2 9.5.5.3 start command this command starts conversions. see the conversion control section for details. table 19 shows the start command byte sequence. table 19. start command direction byte 1 byte 2 byte 3 byte 4 no crc mode din 08h arbitrary dout/ drdy ffh echo byte 1 crc mode din 08h arbitrary crc-2 00h dout/ drdy ffh echo byte 1 echo byte 2 out crc-2 9.5.5.4 stop command this command stops conversions. see the conversion control section for details. table 20 shows the stop command byte sequence. table 20. stop command direction byte 1 byte 2 byte 3 byte 4 no crc mode din 0ah arbitrary dout/ drdy ffh echo byte 1 crc mode din 0ah arbitrary crc-2 00h dout/ drdy ffh echo byte 1 echo byte 2 out crc-2 9.5.5.5 rdata command this command reads conversion data. because the data are buffered, the data can be read at any time during the conversion phase. if data are read near the completion of the next conversion, old or new conversion data are returned. see the data ready ( drdy) section for details. the response of conversion data varies in length from 3 to 5 bytes depending if the status byte and crc bytes are included. see the conversion data format section for the numeric data format. see table 21 , figure 71 (minimum configuration) and figure 72 (maximum configuration) for operation of the rdata command.
53 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated (1) optional status byte table 21. rdata command direction byte 1 byte 2 byte 3 byte 4 byte 5 byte 6 byte 7 byte 8 byte 9 no crc mode din 12h arbitrary 00h 00h 00h 00h dout/ drdy ffh echo byte 1 status (1) msb data mid data lsb data crc mode din 12h arbitrary crc-2 00h 00h 00h 00h 00h 00h dout/ drdy ffh echo byte 1 echo byte 2 out crc-2 status (1) msb data mid data lsb data out crc-3 or out crc-4 (1) cs can be tied low figure 71. conversion data read operation (status byte and crc mode disabled) a. cs can be tied low figure 72. conversion data read operation (status byte and crc mode enabled) 9.5.5.6 syocal command this command is used for system offset calibration. see the offset system-calibration (syocal) section for details. table 22 shows the syocal command byte sequence. table 22. syocal command direction byte 1 byte 2 byte 3 byte 4 no crc mode din 16h arbitrary dout/ drdy ffh echo byte 1 crc mode din 16h arbitrary crc-2 00h dout/ drdy ffh echo byte 1 echo byte 2 out crc-2 cs 1 sclk 9 17 25 dout/drdy din 12h echo byte 2 out crc-2 ffh echo byte 1 arbitrary 33 status crc-2 00h 00h 41 49 msb data 00h 00h 00h mid data lsb data 57 65 out crc-4 00h (1) cs 1 sclk 9 17 25 dout/drdy din 12h msb data mid data ffh echo byte 1 (1) 00h arbitrary 00h 33 lsb data 00h
54 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.5.5.7 gancal command this command is for gain calibration. see the calibration section for details. full-scale calibration (gancal) shows the gancal command byte sequence. table 23. gancal command direction byte 1 byte 2 byte 3 byte 4 no crc mode din 17h arbitrary dout/ drdy ffh echo byte 1 crc mode din 17h arbitrary crc-2 00h dout/ drdy ffh echo byte 1 echo byte 2 out crc-2 9.5.5.8 sfocal command this command is used for self offset calibration. see the offset self-calibration (sfocal) section for details. table 24 shows the sfocal command byte sequence. table 24. sfocal command direction byte 1 byte 2 byte 3 byte 4 no crc mode din 19h arbitrary dout/ drdy ffh echo byte 1 crc mode din 19h arbitrary crc-2 00h dout/ drdy ffh echo byte 1 echo byte 2 out crc-2 (1) rrh = 5-bit register address 9.5.5.9 rreg command use the rreg command to read register data. the register data are read one byte at a time by issuing the rreg command for each operation. add the register address (rrh) to the base opcode (20h) to construct the command byte (20h + rrh). table 25 shows the command byte sequence. the adc responds with the register data byte, most significant bit first. the response to registers outside the valid address range is 00h. figure 73 shows an example of the register read operation. the out crc-1 byte is the crc calculated for the register data byte. table 25. rreg command direction byte 1 byte 2 byte 3 byte 4 byte 5 byte 6 no crc mode din 20h + rrh (1) arbitrary 00h dout/ drdy ffh echo byte 1 register data crc mode din 20h + rrh arbitrary crc-2 00h 00h 00h dout/ drdy ffh echo byte 1 echo byte 2 out crc-2 register data out crc-1
55 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated (1) rrh = 5-bit register address. (1) cs can be tied low figure 73. register read operation (address = 02h, crc mode enabled) 9.5.5.10 wreg command use the wreg command to write register data. the register data are written one byte at a time by issuing the wreg command for each operation. add the register address (rrh) to the base opcode (40h) to construct the command byte (40h + rrh). table 26 shows the command byte sequence. figure 74 shows an example of the wreg operation. be aware that writing to certain registers results in conversion restart. table 29 lists the registers that restart an ongoing conversion when written to. do not write to registers outside the address range. table 26. wreg command direction byte 1 byte 2 byte 3 byte 4 no crc mode din 40h + rrh (1) register data dout/ drdy ffh echo byte 1 crc mode din 40h + rrh register data crc-2 00h dout/ drdy ffh echo byte 1 echo byte 2 out crc-2 a. cs can be tied low figure 74. register write operation (address = 02h, crc mode enabled) cs 1 sclk 9 17 25 dout/drdy din 42h reg data echo byte 2 out crc-2 ffh echo byte 1 (1) crc-2 00h cs 1 sclk 9 17 25 dout/drdy din 22h arbitrary echo byte 2 out crc-2 ffh echo byte 1 (1) crc-2 00h reg data out crc-1 00h 00h 33 41
56 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.5.5.11 lock command the lock command locks-out write access to the registers including the calibration registers that are changed by calibration commands. the default mode is unlock. read access is allowed in lock mode. table 27 shows the lock command byte sequence. table 27. lock command direction byte 1 byte 2 byte 3 byte 4 no crc mode din f2h arbitrary dout/ drdy ffh echo byte 1 crc mode din f2h arbitrary crc-2 00h dout/ drdy ffh echo byte 1 echo byte2 out crc-2 9.5.5.12 unlock command the unlock command allows register write access, including access to the contents of the calibration registers that can be changed by the calibration commands. table 28 shows the unlock command byte sequence. table 28. unlock command direction byte 1 byte 2 byte 3 byte 4 no crc mode din f5h arbitrary dout/ drdy ffh echo byte 1 crc mode din f5h arbitrary crc-2 00h dout/ drdy ffh echo byte 1 echo byte2 out crc-2
57 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.6 register map the register map consists of 19, one-byte registers. collectively, the registers are used to configure the adc to the desired operating mode. access the registers by using the rreg and wreg (read-register and write- register) commands. register data are accessed one register byte at a time for each command operation. at power-on or device reset, the registers are reset to the default values, as shown in the default column of table 29 . writing new data to certain registers causes the adc conversion in progress to restart. these registers are listed in the restart column in table 29 . register-write access is enabled or disabled by the unlock and lock commands, respectively. the default mode is register unlock. see the lock command section for more details. table 29. register map summary (rrh) register default restart bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 00h id xxh dev_id[3:0] rev_id[3:0] 01h status 01h lock crcerr pgal_alm pgah_alm refl_alm drdy clock reset 02h mode0 24h yes dr[4:0] filter[2:0] 03h mode1 01h yes 0 chop[1:0] convrt delay[3:0] 04h mode2 00h gpio_con[3:0] gpio_dir[3:0] 05h mode3 00h pwdn statenb crcenb spitim gpio_dat[3:0] 06h ref 05h yes 0 0 0 refenb rmuxp[1:0] rmuxn[1:0] 07h ofcal0 00h ofc[7:0] 08h ofcal1 00h ofc[15:8] 09h ofcal2 00h ofc[23:16] 0ah fscal0 00h fsc[7:0] 0bh fscal1 00h fsc[15:8] 0ch fscal2 40h fsc[23:16] 0dh imux ffh imux2[3:0] imux1[3:0] 0eh imag 00h imag2[3:0] imag1[3:0] 0fh reserved 00h 00h 10h pga 00h yes bypass 0 0 0 0 gain[2:0] 11h inpmux ffh yes muxp[3:0] muxn[3:0] 12h inpbias 00h yes 0 0 0 vbias bocsp bocs[2:0] 9.6.1 device identification (id) register (address = 00h) [reset = xxh] figure 75. id register 7 6 5 4 3 2 1 0 dev_id[3:0] rev_id[3:0] note: reset values are device dependent legend: r/w = read/write; r = read only; -n = value after reset table 30. id register field descriptions bit field type reset description 7:4 dev_id[3:0] r xh device id 1000: ads1261 1010: ads1260 3:0 rev_id[3:0] r xh revision id note: revision id can change without notification
58 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.6.2 device status (status) register (address = 01h) [reset = 01h] figure 76. status register 7 6 5 4 3 2 1 0 lock crcerr pgal_alm pgah_alm refl_alm drdy clock reset r-0h r/w-0h r-0h r-0h r-0h r-0h r-xh r/w-1h legend: r/w = read/write; r = read only; -n = value after reset table 31. status register field descriptions bit field type reset description 7 lock r 0h register lock status indicates register lock status. register writes are locked by the lock command and unlocked by the unlock command. 0: register write not locked (default) 1: register write locked 6 crcerr r/w 0h crc error indicates that a crc error is detected by the adc. the crc error bit remains set until cleared by the user. 0: no crc error 1: crc error 5 pgal_alm r 0h pga low alarm indicates pga output voltage is below the low limit. the alarm resets at the start of conversion cycles. 0: no alarm 1: alarm 4 pgah_alm r 0h pga high alarm indicates pga output voltage is above the high limit. the alarm resets at the start of conversion cycles. 0: no alarm 1: alarm 3 refl_alm r 0h reference low alarm indicates reference voltage is below the low limit. the alarm resets at the start of conversion cycles. 0: no alarm 1: alarm 2 drdy r 0h data ready indicates conversion data ready. 0: conversion data not new since the previous read operation 1: conversion data new since the previous read operation 1 clock r xh clock indicates internal or external clock mode. the adc automatically selects the clock source. 0: adc clock is internal 1: adc clock is external 0 reset r/w 1h reset indicates adc reset. clear the bit to detect next device reset. 0: no reset 1: reset (default)
59 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.6.3 mode 0 (mode0) register (address = 02h) [reset = 24h] figure 77. mode0 register 7 6 5 4 3 2 1 0 dr[4:0] filter[2:0] r/w-4h r/w-4h legend: r/w = read/write; r = read only; -n = value after reset table 32. mode0 register field descriptions bit field type reset description 7:3 dr[4:0] r/w 4h data rate select the adc data rate. 00000: 2.5 sps 00001: 5 sps 00010: 10 sps 00011: 16. 6 sps 00100: 20 sps (default) 00101: 50 sps 00110: 60 sps 00111: 100 sps 01000: 400 sps 01001: 1200 sps 01010: 2400 sps 01011: 4800 sps 01100: 7200 sps 01101: 14400 sps 01110: 19200 sps 01111: 25600 sps 10000 - 11111: 40000 sps (f clk = 10.24 mhz) 2:0 filter[2:0] r/w 4h digital filter select the digital filter mode. 000: sinc1 001: sinc2 010: sinc3 011: sinc4 100: fir (default) 101: reserved 110: reserved 111: reserved
60 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.6.4 mode 1 (mode1) register (address = 03h) [reset = 01h] figure 78. mode1 register 7 6 5 4 3 2 1 0 0 chop[1:0] convrt delay[3:0] r/w-0h r/w-0h r/w-0h r/w-1h legend: r/w = read/write; r = read only; -n = value after reset table 33. mode1 register field descriptions bit field type reset description 7 0 r/w 0h reserved always write 0 6:5 chop[1:0] r/w 0h chop and ac-excitation modes select the chop and ac-excitation modes. 00: normal mode (default) 01: chop mode 10: 2-wire ac-excitation mode (ads1261 only) 11: 4-wire ac-excitation mode (ads1261 only) 4 convrt r/w 0h adc conversion mode select the adc conversion mode. 0: continuous conversions (default) 1: pulse (one shot) conversion 3:0 delay[3:0] r/w 1h conversion start delay program the time delay at conversion start. delay values are with f clk = 7.3728 mhz. 0000: 0 s (not for 25600 sps or 40000 sps operation) 0001: 50 s (default) 0010: 59 s 0011: 67 s 0100: 85 s 0101: 119 s 0110: 189 s 0111: 328 s 1000: 605 s 1001: 1.16 ms 1010: 2.27 ms 1011: 4.49 ms 1100: 8.93 ms 1101: 17.8 ms 1110: reserved 1111: reserved
61 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.6.5 mode 2 (mode2) register (address = 04h) [reset = 00h] figure 79. mode2 register 7 6 5 4 3 2 1 0 gpio_con[3:0] gpio_dir[3:0] r/w-0h r/w-0h legend: r/w = read/write; r = read only; -n = value after reset (1) ads1261 only table 34. mode2 register field descriptions (1) bit field type reset description 7 gpio_con[3] r/w 0h gpio3 pin connection connect gpio3 to analog input ain5. 0: gpio3 not connected to ain5 (default) 1: gpio3 connected to ain5 6 gpio_con[2] r/w 0h gpio2 pin connection connect gpio2 to analog input ain4. 0: gpio2 not connected to ain4 (default) 1: gpio2 connected to ain4 5 gpio_con[1] r/w 0h gpio1 pin connection connect gpio1 to analog input ain3. 0: gpio1 not connected to ain3 (default) 1: gpio1 connected to ain3 4 gpio_con[0] r/w 0h gpio0 pin connection connect gpio0 to analog input ain2 0: gpio0 not connected to ain2 (default) 1: gpio0 connected to ain2 3 gpio_dir[3] r/w 0h gpio3 pin direction configure gpio3 as a gpio input or gpio output on ain5. 0: gpio3 is an output (default) 1: gpio3 is an input 2 gpio_dir[2] r/w 0h gpio2 pin direction configure gpio2 as a gpio input or gpio output on ain4. 0: gpio2 is an output (default) 1: gpio2 is an input 1 gpio_dir[1] r/w 0h gpio1 pin direction configure gpio1 as a gpio input or gpio output on ain3. 0: gpio1 is an output (default) 1: gpio1 is an input 0 gpio_dir[0] r/w 0h gpio0 pin direction configure gpio0 as a gpio input or gpio output on ain2. 0: gpio0 is an output (default) 1: gpio0 is an input
62 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.6.6 mode 3 (mode3) register (address = 05h) [reset = 00h] figure 80. mode3 register 7 6 5 4 3 2 1 0 pwdn statenb crcenb spitim gpio_dat[3:0] r/w-0h r/w-0h r/w-0h r/w-0h r/w-0h legend: r/w = read/write; r = read only; -n = value after reset (1) ads1261 only table 35. mode3 register field descriptions bit field type reset description 7 pwdn r/w 0h software power-down mode enable the software power-down mode. 0: normal mode (default) 1: software power-down mode 6 statenb r/w 0h status byte enable the status byte in the conversion data read operation. 0: no status byte (default) 1: status byte enabled 5 crcenb r/w 0h crc data verification enable crc data verification. 0: no crc (default) 1: crc enabled 4 spitim r/w 0h spi auto-reset function enable the spi auto-reset function. 0: spi auto-reset disabled (default) 1: spi auto-reset enabled 3 gpio_dat[3] (1) r/w 0h gpio3 data read or write the gpio3 data on ain5. 0: gpio3 is low (default) 1: gpio3 is high 2 gpio_dat[2] (1) r/w 0h gpio2 data read or write the gpio2 data on ain4. 0: gpio2 is low (default) 1: gpio2 is high 1 gpio_dat[1] (1) r/w 0h gpio1 data read or write the gpio1 data on ain3. 0: gpio1 is low (default) 1: gpio1 is high 0 gpio_dat[0] (1) r/w 0h gpio0 data read or write the gpio1 data on ain3. 0: gpio0 is low (default) 1: gpio0 is high
63 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.6.7 reference configuration (ref) register (address = 06h) [reset = 05h] figure 81. ref register 7 6 5 4 3 2 1 0 0 0 0 refenb rmuxp[1:0] rmuxn[1:0] r/w-0h r/w-0h r/w-0h r/w-0h r/w-1h r/w-1h legend: r/w = read/write; r = read only; -n = value after reset table 36. ref register field descriptions bit field type reset description 7:5 0 r/w 0h reserved always write 0h 4 refenb r/w 0h internal reference enable enable the internal reference. 0: internal reference disabled (default) 1: internal reference enabled 3:2 rmuxp[1:0] r/w 1h reference positive input select the positive reference input. 00: internal reference positive 01: avdd internal (default) 10: ain0 external 11: ain2 external (ads1261 only) 1:0 rmuxn[1:0] r/w 1h reference negative input select the negative reference input. 00: internal reference negative 01: avss internal (default) 10: ain1 external 11: ain3 external (ads1261 only)
64 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.6.8 offset calibration (ofcalx) registers (address = 07h, 08h, 09h) [reset = 00h, 00h, 00h] figure 82. ofcal0, ofcal1, ofcal2 registers 7 6 5 4 3 2 1 0 ofc[7:0] r/w-00h 15 14 13 12 11 10 9 8 ofc[15:8] r/w-00h 23 22 21 20 19 18 17 16 ofc[23:16] r/w-00h legend: r/w = read/write; r = read only; -n = value after reset table 37. ofcal0, ofcal1, ofcal2 registers field description bit field type reset description 23:0 ofc[23:0] r/w 000000h offset calibration these three registers are the 24-bit offset calibration word. the offset calibration is two's complement format. the adc subtracts the offset value from the conversion result before the full-scale operation. 9.6.9 full-scale calibration (fscalx) registers (address = 0ah, 0bh, 0ch) [reset = 00h, 00h, 40h] figure 83. fscal0, fscal1, fscal2 registers 7 6 5 4 3 2 1 0 fsc[7:0] r/w-00h 15 14 13 12 11 10 9 8 fsc[15:8] r/w-00h 23 22 21 20 19 18 17 16 fsc[23:16] r/w-40h legend: r/w = read/write; r = read only; -n = value after reset table 38. fscal0, fscal1, fscal2 registers field description bit field type reset description 23:0 fsc[23:0] r/w 400000h full-scale calibration these three registers are the 24-bit full scale calibration word. the full-scale calibration is straight binary format. the adc divides the register value by 400000h then multiplies the result with the conversion data. the scaling operation occurs after the offset operation.
65 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.6.10 idac multiplexer (imux) register (address = 0dh) [reset = ffh] figure 84. imux register 7 6 5 4 3 2 1 0 imux2[3:0] imux1[3:0] r/w-fh r/w-fh legend: r/w = read/write; r = read only; -n = value after reset table 39. imux register field descriptions bit field type reset description 7:4 imux2[3:0] r/w fh idac2 output multiplexer select the idac2 analog input pin connection. 0000: ain0 0001: ain1 0010: ain2 0011: ain3 0100: ain4 0101: ain5 (ads1261 only) 0110: ain6 (ads1261 only) 0111: ain7 (ads1261 only) 1000: ain8 (ads1261 only) 1001: ain9 (ads1261 only) 1010: aincom 1011: no connection 1100: no connection 1101: no connection 1110: no connection 1111: no connection (default) 3:0 imux1[3:0] r/w fh idac1 output multiplexer select the idac1 analog input pin connection. 0000: ain0 0001: ain1 0010: ain2 0011: ain3 0100: ain4 0101: ain5 (ads1261 only) 0110: ain6 (ads1261 only) 0111: ain7 (ads1261 only) 1000: ain8 (ads1261 only) 1001: ain9 (ads1261 only) 1010: aincom 1011: no connection 1100: no connection 1101: no connection 1110: no connection 1111: no connection (default)
66 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.6.11 idac magnitude (imag) register (address = 0eh) [reset = 00h] figure 85. imag register 7 6 5 4 3 2 1 0 imag2[3:0] imag1[3:0] r/w-0h r/w-0h legend: r/w = read/write; r = read only; -n = value after reset table 40. imag register field descriptions bit field type reset description 7:4 imag2[3:0] r/w 0h idac2 current magnitude select the magnitude of current source idac2. 0000: off (default) 0001: 50 a 0010: 100 a 0011: 250 a 0100: 500 a 0101: 750 a 0110: 1000 a 0111: 1500 a 1000: 2000 a 1001: 2500 a 1010: 3000 a 1011: off 1100: off 1101: off 1110: off 1111: off 3:0 imag1[3:0] r/w 0h idac1 current magnitude select the magnitude of current source idac1. 0000: off (default) 0001: 50 a 0010: 100 a 0011: 250 a 0100: 500 a 0101: 750 a 0110: 1000 a 0111: 1500 a 1000: 2000 a 1001: 2500 a 1010: 3000 a 1011: off 1100: off 1101: off 1110: off 1111: off
67 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.6.12 reserved (reserved) register (address = 0fh) [reset = 00h] figure 86. reserved register 7 6 5 4 3 2 1 0 0 0 0 0 0 0 0 0 r-0h r-0h r-0h r-0h r-0h r-0h r-0h r-0h legend: r/w = read/write; r = read only; -n = value after reset table 41. reserved register field descriptions bit field type reset description 7:0 0 r 0h reserved these bits are read only and always return 0 9.6.13 pga configuration (pga) register (address = 10h) [reset = 00h] figure 87. pga register 7 6 5 4 3 2 1 0 bypass 0 0 0 0 gain[2:0] r/w-0h r/w-0h r/w-0h r/w-0h r/w-0h r/w-0h legend: r/w = read/write; r = read only; -n = value after reset table 42. pga register field descriptions bit field type reset description 7 bypass r/w 0h pga bypass mode select the pga mode. 0: pga mode (default) 1: pga bypass 6:3 0 r/w 0h reserved always write 0 2:0 gain[2:0] r/w 0h gain select the gain. 000: 1 (default) 001: 2 010: 4 011: 8 100: 16 101: 32 110: 64 111: 128
68 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.6.14 input multiplexer (inpmux) register (address = 11h) [reset = ffh] figure 88. inpmux register 7 6 5 4 3 2 1 0 muxp[3:0] muxn[3:0] r/w-fh r/w-fh legend: r/w = read/write; r = read only; -n = value after reset table 43. inpmux register field descriptions bit field type reset description 7:4 muxp[3:0] r/w fh positive input multiplexer select the positive multiplexer input. 0000: aincom 0001: ain0 0010: ain1 0011: ain2 0100: ain3 0101: ain4 0110: ain5 (ads1261 only) 0111: ain6 (ads1261 only) 1000: ain7 (ads1261 only) 1001: ain8 (ads1261 only) 1010: ain9 (ads1261 only) 1011: internal temperature sensor positive 1100: internal (avdd - avss) / 4 positive 1101: internal (dvdd / 4) positive 1110: inputs open 1111: internal connection to v com (default) 3:0 muxn[3:0] r/w fh negative input multiplexer select the negative multiplexer input. 0000: aincom 0001: ain0 0010: ain1 0011: ain2 0100: ain3 0101: ain4 0110: ain5 (ads1261 only) 0111: ain6 (ads1261 only) 1000: ain7 (ads1261 only) 1001: ain8 (ads1261 only) 1010: ain9 (ads1261 only) 1011: internal temperature sensor negative 1100: internal (avdd - avss) / 4 negative 1101: internal (dvdd / 4) negative 1110: all inputs open 1111: internal connection to v com (default)
69 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 9.6.15 input bias (inpbias) register (address = 12h) [reset = 00h] figure 89. inpbias register 7 6 5 4 3 2 1 0 0 0 0 vbias bocsp bocs[2:0] r/w-0h r/w-0h r/w-0h r/w-0h r/w-0h r/w-0h legend: r/w = read/write; r = read only; -n = value after reset table 44. inpbias register field descriptions bit field type reset description 7:5 0 r/w 0h reserved always write 0 4 vbias r/w 0h vbias select the vbias connection to the aincom pin. 0: vbias disabled (default) 1: vbias enabled 3 bocsp r/w 0h burn-out current source polarity select the burn-out current source polarity. 0: pull-up mode (default) 1: pull-down mode 2:0 bocs[2:0] r/w 0h burn-out current source magnitude select the burn-out current source magnitude. 000: off (default) 001: 50 na 010: 200 na 011: 1 a 100: 10 a 101: reserved 110: reserved 111: reserved
70 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 10 application and implementation note information in the following applications sections is not part of the ti component specification, and ti does not warrant its accuracy or completeness. ti ? s customers are responsible for determining suitability of components for their purposes. customers should validate and test their design implementation to confirm system functionality. 10.1 application information 10.1.1 input range in pga mode, the input voltage must be within the specified input range for linear operation. the following exercise shows how to use equation 5 to verify the input voltage is within specification. the exercise is a thermocouple with the negative lead connected to aincom and the level-shift voltage enabled (2.5 v). the gain factor = 32 and the adc is powered by a single 5-v power supply. the summary of conditions are: ? v ainn = negative absolute input voltage = 2.5 v ? v ainp = positive absolute input voltage = 2.56 v ? v in = differential input voltage = 60 mv ? avdd = 4.75 v (worst-case minimum) ? avss = 0 v ? gain = 32 evaluation of the equation results in: 1.23 v < 2.5 v and 2.56 v < 3.52 v the inequality is satisfied, therefore the absolute input voltages are within the specified pga input range. the input requirement can also be verified by measuring the pga output voltages (pins capp and capn) with a voltmeter. check that both outputs are within the range: avss + 0.3 v < v (capp) and v (capn) < avdd ? 0.3 v, under the worst-case input and power-supply conditions. 10.1.2 input overload observe the input overvoltage precautions as outlined in the esd diodes section. if an overvoltage condition occurs on an unused channel, the overvoltage channel may crosstalk to the measurement channel. one solution is to externally clamp the inputs with low-forward voltage diodes as shown in figure 90 . the external diodes divert the overvoltage current around the adc inputs to the power supply and ground. be aware of the reverse leakage current of the schottky diodes that may lead to measurement errors. figure 90. external diode clamps avdd schottky diode ainx avss i fault schottky diode i fault 5 v avss 0.3 v > v clamp > avdd + 0.3 v adc r lim
71 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated application information (continued) 10.1.3 burn-out current source when using the burn-out current sources, be aware of the offset error caused by the currents flowing through impedances in the input path, including the multiplexer resistance ? mux ), external filter resistors and the internal impedance of the sensor ? ext ), as shown in figure 91 . in many cases, the offset error can be calibrated. be aware that the combination of chop mode and high data rates increases the input current to the pga. the increased input current can affect the accuracy of the burn-out current sources. figure 91. burn-out current source offset voltage error 10.1.4 unused inputs and outputs ? analog inputs to minimize input leakage of the measurement channel, tie unused inputs to mid-supply voltage (avdd + avss) / 2 or to avdd. ? digital i/o not all the digital i/os may be needed to operate the adc. be sure not to float both used and unused digital inputs, including during power-down mode. the following is a summary of the optional digital i/os connection: ? cs: tie cs low to permanently enable the serial interface. ? clkin: tie clkin to dgnd to permanently operate the adc with the internal oscillator. ? start: tie start to dgnd to control conversions by command. tie start to dvdd to permanently free-run conversions (continuous-conversion mode only) ? reset: tie reset to dvdd if not using hardware reset. the adc is reset at power-on. the adc is also reset by the reset command. ? pwdn: tie pwdn to dvdd if not using the hardware power-down mode. the adc can be powered down by software. ? drdy: the functionality of the drdy output is also provided by the dual-mode dout/ drdy pin. the dout/ drdy output is active when cs is low. data ready is also determined by software polling. because the conversion data are buffered, data can be read at any time without the need to synchronize to data ready. avdd pga avss r mux r mux ainx ainx r ext r ext + v sensor v in = v sensor + v offset i bocs i bocs
72 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated application information (continued) 10.1.5 ac-excitation figure 92 shows a example of an ac-excited bridge measurement system. the example shown omits optional filter components for clarity. the transistors switch the bridge excitation voltage by drive signals provided by the gpio drivers through the analog input pins. the timing of the drive signals are synchronized to the adc conversions. the drive signals do not overlap in order to avoid bridge commutation during the switching phase of the drive signal. the transistors gate resistors bias the transistors off at power-on. at host start-up, the host configures the adc to the ac-excitation mode. see figure 7 for timing of the drive signals. figure 92. 4-wire drive, ac-excitation example the recommended sequence ac-excitation configuration is as follows: 1. stop conversions by taking the start pin low, or by control of conversions in software mode; send the stop command 2. program the input and reference mux, gain, data rata, filter mode and other configurations as needed 3. program the 2-wire or 4-wire ac-excitation mode 4. program the 2 gpios or 4 gpios internal connection to the analog input pins 5. program the 2 gpios or 4 gpios as outputs to enable drive signals at the analog input pins. start the conversions. adjust the time delay parameter as necessary based on the time constant of the input and reference filters. 100 n? 5 v 100 n? (acx1) (acx2) ads1261 (refp0) (refn0) ain6 ain7 sig + sig - sen + sen - ain0 ain1 ain5 ain2 (ainp) (ainn) 100 n? 5 v 100 n? ain4 ain3 (acx2) (acx1) avss avdd 5 v
73 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated application information (continued) 10.1.6 serial interface and digital connections figure 93 shows an example of the digital connections from a host c to the adc. not all i/o connections are necessary for basic adc operation; see unused inputs and outputs . impedance-matching resistors in series with the i/o pcb traces help reduce overshoot and ringing, and is particularly helpful over long trace runs. figure 93. serial interface and digital i/o connections port pin (cs) sclk mosi miso 47 47 47 ,54 ; host c port pin 47 adc 47 start cs sclk din dout /drdy 47 drdy port pin 47 reset optional clock source 47 clkin port pin 47 pwdn
74 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 10.2 typical application figure 94 shows a fault-protected, 3-wire rtd application with hardware-based, lead-wire compensation. two current sources are used together to compensate the rtd lead wire resistance. one current source (idac1) provides excitation to the rtd element through r lead1 . the reference voltage of the adc is derived directly from this current by resistor r ref . the second current source cancels lead-wire resistance by generating a voltage drop on lead-wire resistance r lead2 equal to the voltage drop of r lead1 . because the r rtd signal voltage is measured differentially via inputs ain2 and ain3, the voltages across the lead wire resistance cancel. resistor r bias level-shifts the rtd signal voltage to within the adc input range. the current sources route to the rtd element through low v f diodes to provide input fault protection. figure 94. rtd element with 3-wire lead resistance compensation 10.2.1 design requirements the key considerations in the design of a 3-wire rtd circuit are the accuracy, stability and noise of the measurement, accuracy of the lead-wire compensation and self-heating of the sensor. stability of the measurement is determined by the offset and gain drift of the adc and by the drift of the external reference resistor. measurement noise is determined by the adc sample rate and by the digital filter settings. these parameters are not summarized here. table 45 summarizes the basic design goals for a 3-wire pt100 rtd. table 45. design goals design parameter value rtd sensor type 3-wire pt100 rtd resistance range 20 to 400 rtd lead resistance range 0 to 10 rtd self heating < 1 mw dout/drdy pwdn din ain2 ain3 ain4 c dif1 c cm1 c cm2 r f2 r f1 r lead2 r lead1 r rtd (idac2) (refp0) i idac1 + i idac2 clock mux clkin c dif2 c cm3 c cm4 r f4 r f3 ain0 ain1 aincom 5 v 0.1 p f adc pga r lead3 500 a idac2 3-wire rtd i idac2 i idac1 r ref r bias 500 a idac1 (refn0) (idac1) avdd avdd avdd dvdd avss dgnd internal reference digital filter serial interface and control cs sclk drdy reset ref mon signal mon buf reference mux 3.3 v 1 f refout internal oscillator input mux start ads1260 ads1261 p f p f capp 4.7 nf c0g capn bypass 1 f
75 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated table 46 summarize the parameters of the detailed design procedure that follows. table 46. design parameters design parameter design value i idac idac current 500 a p rtd rtd power dissipation 0.1 mw v rtd rtd input voltage 0.20 v gain adc gain 8 v ref reference voltage (design target allows for 10% overrange) 1.76 v r ref reference resistor (senses the idac current to generate v ref ) 3.52 k r bias bias resistor (provides the rtd level-shift voltage) 1.10 k v rtdn rtd negative input voltage 1.1 v v rtdp rtd positive input voltage 1.31 v v idac1 idac1 loop voltage 3.37 v 10.2.2 detailed design procedure idac1 current flows through reference resistor, r ref , which generates the adc reference voltage, v ref = i idac1 r ref . idac1 current also flows through the rtd element. since the same current flows through r ref and the rtd element, the rtd measurement is ratiometric, which means the drift and error of the current source are cancelled. therefore, the measurement accuracy is solely dependent on the tolerance of r ref and on adc gain and offset errors. the errors are calibrated by host software control using shorted-input calibration and using a 400 precision resistor for full-scale calibration. the current of idac2 is programmed to the same value as idac1 and is connected to r lead2 . idac2 generates an equal voltage drop across r lead1 and idac1. the accuracy of lead-wire compensation depends on the matching error between idac1 to idac2. using r rtd = 400 , idac current = 500 a, and gain = 8, the minimum adc reference voltage requirement calculates to 1.6 v. to provide 10% design margin, r ref calculates to 3.52 k (1.76 v / 500 a). 500 a is selected to minimize heating of the sensor. resistor r bias level-shifts the rtd voltage to meet the input range requirement of the adc. this voltage is v rtdn and the low limit is calculated by equation 8 . the v rtdn low limit is 1 v. avss + 0.3 v + v rtd (gain ? 1) / 2 v rtdn (8) using 10% design margin, r bias calculates to 1.1 k = 1.1 v / (2 500 a). the next step is to verify the positive rtd voltage (v rtdp ) does not exceed the maximum input range, as shown in equation 9 : maximum v rtdp avdd ? 0.3 v ? v rtd (gain ? 1) / 2 (9) evaluation of the equation results in the v rtdp high limit = 3.75 v. calculate the actual v rtdp input voltage by equation 10 : actual v rtdp = v rtdn + i idac1 ( r rtd + 2 r lead ) = 1.1 v + 500 a (400 + 20 ) = 1.31 v (10) v rtdn = 1.1 v and v rtdp = 1.31 v satisfy the negative and positive input voltage requirements of the adc, respectively. verify the burden voltage of current source idac1 is below the specified compliance range. the burden voltage is the sum of voltages in the idac1 loop as calculated by v rtdp + (idac1 r ref ) + v d ( v d = external diode voltage). the result is 3.37 v, which meets the specified compliance voltage of the current source. external filter components ? f1 , r f2 , c dif1 , c cm1 , c cm2 ) and ? f3 , r f4 , c dif2 , c cm3 , and c cm4 ) filter the signal and reference inputs of the adc. the filters remove both differential and common-mode noise. the input signal differential filter cutoff frequency as calculated by equation 11 : f dif = 1 / [2 ? f1 + r f2 ) ? dif1 + c m1 || c m2 )] (11) the input signal common-mode filter is calculated by equation 12 : f cm = 1 / (2 r f1 c m1 ) = 1 / (2 r f2 c m2 ) (12)
76 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated component mismatch in the common-mode filter converts common-mode noise into differential noise. use a differential capacitor c dif1 10 higher value than the common-mode capacitors, c cm1 and c cm2 to minimize the effects of mismatch. the recommended range of input resistors is 1 k to 10 k ; increasing the resistance beyond 10 k beyond could compromise noise and drift performance of the adc. use high-quality c0g ceramics or film-type capacitors. for consistent noise performance across the full rtd temperature range, match the corner frequencies of the input and reference filters. detailed information is found in the rtd ratiometric measurements and filtering using the ads1148 and ads1248 family of devices application report 10.2.3 application curves figure 95 shows the resistance measurement results. the measurements are taken at t a = 25 c. the data are taken using a precision resistor simulator with a 3-wire connection in place of the rtd. a system offset calibration is performed using shorted inputs. a system gain calibration is performed using a 390- precision resistor. the measurement data are in ohms and do not include the error of the rtd sensor. the measured resistance error is < 0.02 over the 20- to 400- range. figure 95. 3-wire rtd example measurement results rtd value ( : ) measurement error ( : ) 0 50 100 150 200 250 300 350 400 -0.1 -0.05 0 0.05 0.1
77 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 10.3 initialization setup figure 96 shows a general configuration and measurement procedure. figure 96. adc configuration and measurement procedure power on /* drdy is held low at power-on until ready for communicatio n set reset and pwdn high /* these pins must be high for operation start high? n y /* if start pin is low, conversions are stopped configure the adc external clock? apply clock to clkin y /* adc automatically detects external clock n verify registers wait for reference voltage to settle set start pin high or start command /* readback register data for verification /* the internal reference requires time to settle after power -on /* start or restart new adc conversion set start low or stop command drdy pin low ? n y read data change adc settings ? n y /* read data at a rate faster than the data rate to avoid missed data /* for simplicity, stop conversions before register configuration hardware drdy? y read status register drdy bit asserted ? n n y drdy not pulsing drdy pulses at 20 hz drdy pin high? y n /* new data when drdy bit =1 /* write register data, crc verfication is optional
78 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 11 power supply recommendations the adc requires an analog power supply (avdd, avss) and digital power supply (dvdd). the analog power supply can be bipolar (avdd = +2.5 v and avss = ? 2.5 v) or unipolar (avdd = 5 v and avss = dgnd). the digital supply range is 2.7 v to 5.25 v. dvdd powers the adc core by use of an internal regulator. dvdd also sets the digital i/o voltage. keep in mind that the gpio i/o voltages are avdd and avss. voltage ripple produced by switch-mode power supplies may interfere with the adc conversions. use low-dropout regulators (ldos) to reduce switch-mode power supply ripple. 11.1 power-supply decoupling good power-supply decoupling is important in order to achieve optimum performance. power supplies must be decoupled close to the power supply pins using short, direct connections to ground. for the analog supply, place 0.1- f and 10- f capacitors between avdd and avss and 0.1- f capacitors from each supply to ground. connect a 1- f capacitor from dvdd to the ground plane. connect a 1- f capacitor from bypass to the ground plane. 11.2 analog power-supply clamp it is important to evaluate circumstances when an input signal is present with the adc, both powered and unpowered. when the input signal exceeds the power-supply voltage, it is possible to backdrive the analog power-supply voltage with the input signal through a conduction path of the internal esd diodes. backdriving the adc power supply can also occur when the power-supply is on. the backdriven current path is illustrated in figure 97 . depending on how the power supply responds during a backdriven condition, it is possible to exceed the maximum rated adc supply voltage. the adc voltage must not be exceeded at all times. one solution is to clamp the analog supply to safe voltage using an external zener diode. figure 97. analog power-supply clamp 11.3 power-supply sequencing the power supplies can be sequenced in any order, but do not allow the analog or digital inputs to exceed the respective analog or digital power-supplies without external limits of the possible input fault currents. avdd esd diode ainx + input voltage esd diode r limit +5 v reg avss optional 6-v zener diode i fault i fault adc supply on or off +v ainx i fault adc
79 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 12 layout good layout practices are crucial to realize the full-performance of the adc. poor grounding can quickly degrade the noise performance. the following layout guidelines help provide the best results. 12.1 layout guidelines for best performance, dedicate an entire pcb layer to a ground plane and do not route any other signal traces on this layer. however, depending on restrictions imposed by specific end equipment, a dedicated ground plane may not be practical. if ground plane separation is necessary, make a direct connection of the planes at the adc. do not connect individual ground planes at multiple locations because this configuration creates ground loops. route digital traces away from the capp and capn pins, away from the refout pin, and away from all analog inputs and associated components in order to minimize interference. avoid long traces on dout/ drdy, because high capacitance on this pin can lead to increase of adc noise levels. use a series resistor or a buffer if long traces are used. the internal reference output return shares the same pin as the avss power supply. to minimize coupling between the power supply and reference-return trace, route the traces separately; ideally, as a star connection to the avss pin. use c0g capacitors on the analog inputs and for the capp to capn capacitor. use ceramic capacitors (for example, x7r grade) for the power supply decoupling capacitors. high-k capacitors (y5v) are not recommended. the refout pin requires a 10- f capacitor and can be either ceramic or tantalum type. place the required capacitors as close as possible to the device pins using short, direct traces. for optimum performance, use low-impedance connections on the ground-side connections of the bypass capacitors. when applying an external clock, be sure the clock is free of overshoot and glitches. a source-termination resistor placed at the clock buffer often helps reduce overshoot. glitches present on the clock input can lead to noise within the conversion data. 12.2 layout example figure 98 is an example layout of the ads1261, requiring a minimum of three pcb layers. the example circuit is shown with single supply operation (avss = dgnd). in this example, the inner layer is dedicated to the ground plane and the outer layers are used for signal and power traces. if a four-layer pcb is used, dedicate the additional inner layer as the power plane. in this example, the adc is oriented in such a way to minimize crossover of the analog and digital signal traces.
80 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated layout example (continued) figure 98. ads1261 layout example for unipolar supply, avss = gnd 16 15 14 13 12 11 10 9 nc 24 23 22 21 20 19 18 17 25 26 27 28 29 30 31 32 to mcu 12 3 4 5 6 78 to analog circuitry connect thermal pad to avss (leave nc pins floating) 10 f avdd supply dvdd supply 4.7 nf (0603 shown) c0g c0g c0g c0g c0g (differential input pair) (differential input pair) (differential input pair) (differential input pair) (differential input pair) ads1261 1 f (9-mil traces shown) reference output adc clock options: option 2: connect external clock source to clkin option 1 : to enable internal oscillator, tie clkin to gnd ain8 ain9 nc nc nc clkin dvdd ain7 ain6 ain5 ain4 ain3 ain2 ain1 ain0 dgnd bypass drdy din sclk cs start aincom capp capn avdd avss refout pwdn reset dout/ drdy (0805 shown) 1 f 1 f 10 f (0805 shown) c0g
81 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated 13 device and documentation support 13.1 documentation support 13.1.1 related documentation for related documentation see the following: ads1261 evaluation module user ' s guide 13.2 related links table 47 lists quick access links. categories include technical documents, support and community resources, tools and software, and quick access to order now. table 47. related links parts product folder order now technical documents tools & software support & community ads1260 preview preview preview preview preview ads1261 click here click here click here click here click here 13.3 receiving notification of documentation updates to receive notification of documentation updates, navigate to the device product folder on ti.com. in the upper right corner, click on alert me to register and receive a weekly digest of any product information that has changed. for change details, review the revision history included in any revised document. 13.4 community resources the following links connect to ti community resources. linked contents are provided "as is" by the respective contributors. they do not constitute ti specifications and do not necessarily reflect ti's views; see ti's terms of use . ti e2e ? online community ti's engineer-to-engineer (e2e) community. created to foster collaboration among engineers. at e2e.ti.com, you can ask questions, share knowledge, explore ideas and help solve problems with fellow engineers. design support ti's design support quickly find helpful e2e forums along with design support tools and contact information for technical support. 13.5 trademarks e2e is a trademark of texas instruments. all other trademarks are the property of their respective owners. 13.6 electrostatic discharge caution this integrated circuit can be damaged by esd. texas instruments recommends that all integrated circuits be handled with appropriate precautions. failure to observe proper handling and installation procedures can cause damage. esd damage can range from subtle performance degradation to complete device failure. precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications. 13.7 glossary slyz022 ? ti glossary . this glossary lists and explains terms, acronyms, and definitions. 14 mechanical, packaging, and orderable information the following pages include mechanical packaging and orderable information. this information is the most current data available for the designated devices. this data is subject to change without notice and revision of this document. for browser-based versions of this data sheet, refer to the left-hand navigation.
82 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated www.ti.com package outline c 32x 0.30.2 3.45 0.1 32x 0.50.3 1 max (0.2) typ 0.050.00 28x 0.5 2x 3.5 2x 3.5 a 5.14.9 b 5.14.9 vqfn - 1 mm max height rhb0032e plastic quad flatpack - no lead 4223442/a 11/2016 pin 1 index area 0.08 c seating plane 1 8 17 24 9 16 32 25 (optional) pin 1 id 0.1 c a b 0.05 c exposed thermal pad 33 symm symm notes: 1. all linear dimensions are in millimeters. any dimensions in parenthesis are for reference only. dimensioning and tolerancing per asme y14.5m. 2. this drawing is subject to change without notice. 3. the package thermal pad must be soldered to the printed circuit board for thermal and mechanical performance. scale 3.000
83 ads1260 , ads1261 www.ti.com sbas760a ? march 2018 ? revised may 2018 ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated www.ti.com example board layout (1.475) 0.07 min all around 0.07 max all around 32x (0.25) 32x (0.6) ( 0.2) typ via 28x (0.5) (4.8) (4.8) (1.475) ( 3.45) (r0.05) typ vqfn - 1 mm max height rhb0032e plastic quad flatpack - no lead 4223442/a 11/2016 symm 1 8 9 16 17 24 25 32 symm land pattern example scale:18x notes: (continued) 4. this package is designed to be soldered to a thermal pad on the board. for more information, see texas instruments literature number slua271 (www.ti.com/lit/slua271). 5. vias are optional depending on application, refer to device data sheet. if any vias are implemented, refer to their locations shown on this view. it is recommended that vias under paste be filled, plugged or tented. 33 solder maskopening metal under solder mask solder mask defined metal solder maskopening non solder mask solder mask details defined (preferred)
84 ads1260 , ads1261 sbas760a ? march 2018 ? revised may 2018 www.ti.com ads1261 submit documentation feedback copyright ? 2018, texas instruments incorporated www.ti.com example stencil design 32x (0.6) 32x (0.25) 28x (0.5) (4.8) (4.8) 4x ( 1.49) (0.845) (0.845) (r0.05) typ vqfn - 1 mm max height rhb0032e plastic quad flatpack - no lead 4223442/a 11/2016 notes: (continued) 6. laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. ipc-7525 may have alternate design recommendations. 33 symm metal typ based on 0.125 mm thick stencil solder paste example exposed pad 33: 75% printed solder coverage by area under package scale:20x symm 1 8 9 16 17 24 25 32
package option addendum www.ti.com 2-jun-2018 addendum-page 1 packaging information orderable device status (1) package type package drawing pins package qty eco plan (2) lead/ball finish (6) msl peak temp (3) op temp (c) device marking (4/5) samples ads1261irhbr active vqfn rhb 32 3000 green (rohs & no sb/br) cu nipdau level-3-260c-168 hr -40 to 125 ads 1261 ads1261irhbt active vqfn rhb 32 250 green (rohs & no sb/br) cu nipdau level-3-260c-168 hr -40 to 125 ads 1261 PADS1261IRHBT active vqfn rhb 32 250 tbd call ti call ti -40 to 125 (1) the marketing status values are defined as follows: active: product device recommended for new designs. lifebuy: ti has announced that the device will be discontinued, and a lifetime-buy period is in effect. nrnd: not recommended for new designs. device is in production to support existing customers, but ti does not recommend using this part in a new design. preview: device has been announced but is not in production. samples may or may not be available. obsolete: ti has discontinued the production of the device. (2) rohs: ti defines "rohs" to mean semiconductor products that are compliant with the current eu rohs requirements for all 10 rohs substances, including the requirement that rohs substance do not exceed 0.1% by weight in homogeneous materials. where designed to be soldered at high temperatures, "rohs" products are suitable for use in specified lead-free processes. ti may reference these types of products as "pb-free". rohs exempt: ti defines "rohs exempt" to mean products that contain lead but are compliant with eu rohs pursuant to a specific eu rohs exemption. green: ti defines "green" to mean the content of chlorine (cl) and bromine (br) based flame retardants meet js709b low halogen requirements of <=1000ppm threshold. antimony trioxide based flame retardants must also meet the <=1000ppm threshold requirement. (3) msl, peak temp. - the moisture sensitivity level rating according to the jedec industry standard classifications, and peak solder temperature. (4) there may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device. (5) multiple device markings will be inside parentheses. only one device marking contained in parentheses and separated by a "~" will appear on a device. if a line is indented then it is a continuation of the previous line and the two combined represent the entire device marking for that device. (6) lead/ball finish - orderable devices may have multiple material finish options. finish options are separated by a vertical ruled line. lead/ball finish values may wrap to two lines if the finish value exceeds the maximum column width. important information and disclaimer: the information provided on this page represents ti's knowledge and belief as of the date that it is provided. ti bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the accuracy of such information. efforts are underway to better integrate information from third parties. ti has taken and continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals. ti and ti suppliers consider certain information to be proprietary, and thus cas numbers and other limited information may not be available for release.
package option addendum www.ti.com 2-jun-2018 addendum-page 2 in no event shall ti's liability arising out of such information exceed the total purchase price of the ti part(s) at issue in this document sold by ti to customer on an annual basis.
tape and reel information *all dimensions are nominal device package type package drawing pins spq reel diameter (mm) reel width w1 (mm) a0 (mm) b0 (mm) k0 (mm) p1 (mm) w (mm) pin1 quadrant ads1261irhbr vqfn rhb 32 3000 330.0 12.4 5.3 5.3 1.1 8.0 12.0 q2 ads1261irhbt vqfn rhb 32 250 180.0 12.4 5.3 5.3 1.1 8.0 12.0 q2 package materials information www.ti.com 3-jun-2018 pack materials-page 1
*all dimensions are nominal device package type package drawing pins spq length (mm) width (mm) height (mm) ads1261irhbr vqfn rhb 32 3000 367.0 367.0 35.0 ads1261irhbt vqfn rhb 32 250 210.0 185.0 35.0 package materials information www.ti.com 3-jun-2018 pack materials-page 2
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