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1 for more information www.linear.com/LTC2983 typical a pplica t ion fea t ures descrip t ion multi- sensor high accuracy digital temperature measurement system the lt c ? 2983 measures a wide variety of temperature sensors and digitally outputs the result, in c or f, with 0.1c accuracy and 0.001 c resolution. the LTC2983 can measure the temperature of virtually all standard ( type b, e, j, k, n, s, r, t) or custom thermocouples, automatically compensate for cold junction temperatures and linearize the results. the device can also measure temperature with standard 2-, 3-, or 4- wire rtds, thermistors, and diodes. it has 20 reconfigurable analog inputs enabling many sen - sor connections and configuration options. the LTC2983 includes excitation current sources and fault detection circuitry appropriate for each type of temperature sensor. the LTC2983 allows direct interfacing to ground referenced sensors without the need for level shifters, negative supply voltages, or external amplifiers. all signals are buffered and simultaneously digitized with three high accuracy, 24-bit ? adc 's , driven by an internal 10ppm/c ( maximum) reference . thermocouple measurement with automatic cold junction compensation typical temperature error a pplica t ions l, lt , lt c , lt m , linear technology and the linear logo are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. patents pending n directly digitize rtds, thermocouples, thermistors, and diodes n single 2.85v to 5.25v supply n results reported in c or f n 20 flexible inputs allow interchanging sensors n automatic thermocouple cold junction compensation n built- in standard and user- programmable coefficients for thermocouples, rtds and thermistors n configurable 2-, 3-, or 4-wire rtd configurations n measures negative thermocouple voltages n automatic burn out, short - circuit and fault detection n buffered inputs allow external protection n simultaneous 50hz/60hz rejection n includes 10ppm/c (max) reference (i-grade) n direct thermocouple measurements n direct rtd measurements n direct thermistor measurements n custom sensor applications 2983 ta01a c/f v ref (10ppm/c) LTC2983 24-bit ? adc 24-bit ? adc 24-bit ? adc r sense 2k 1 4 2 3 0.1f 2.85v to 5.25v 1k 1k pt-100 rtd linearization/ fault detection spi interface temperature (c) ?200 ?0.5 error (c) 0.3 0.2 0.1 ?0.1 ?0.2 ?0.3 ?0.4 0.5 200 600 800 2983 ta01b 0 0.4 0 400 1000 14001200 thermistor thermocouple rtd 3904 diode ltc 2983 2983f
2 for more information www.linear.com/LTC2983 table o f c on t en t s features ............................................................................................................................ 1 applications ....................................................................................................................... 1 t ypical application ............................................................................................................... 1 description ......................................................................................................................... 1 absolute maximum ratings ..................................................................................................... 3 order information ................................................................................................................. 3 pin configuration ................................................................................................................. 3 complete system electrical characteristics .................................................................................. 3 adc electrical characteristics .................................................................................................. 4 reference electrical characteristics ........................................................................................... 4 digital inputs and digital outputs .............................................................................................. 5 t ypical performance characteristics .......................................................................................... 6 pin functions ...................................................................................................................... 9 block diagram .................................................................................................................... 10 t est circuits ...................................................................................................................... 11 t iming diagram .................................................................................................................. 11 over view .......................................................................................................................... 12 applications information ....................................................................................................... 16 thermocouple measurements .............................................................................................................................. 21 diode measurements ............................................................................................................................................ 24 r td measurements .............................................................................................................................................. 28 thermistor measurements .................................................................................................................................... 43 supplemental information ...................................................................................................... 55 direct adc measurements .................................................................................................................................... 55 fault protection and anti-aliasing ......................................................................................................................... 57 2- and 3-cycle conversion modes ........................................................................................................................ 57 running conversions consecutively on multiple channels ................................................................................... 58 mux configuration delay ...................................................................................................................................... 58 global configuration register ............................................................................................................................... 59 custom thermocouples ......................................................................................................... 59 custom r tds ..................................................................................................................... 62 custom thermistors ............................................................................................................. 65 package description ............................................................................................................ 71 t ypical application .............................................................................................................. 72 related parts ..................................................................................................................... 72 ltc 2983 2983f
3 for more information www.linear.com/LTC2983 p in c on f igura t ion a bsolu t e maxi m u m r a t ings supply voltage (v dd ) ................................... C0. 3 v to 6v analog input pins ( ch 1 to ch 20, com) ................................. C 0.3 v to (v dd + 0.3 v) input current ( ch 1 to ch 20, com) ...................... 1 5 ma digital inputs ( cs , sdi , sck , reset ) ................................ C 0.3 v to (v dd + 0.3 v) digital outputs ( sdo , interrupt ) C0. 3 v to (v dd + 0.3 v) v refp ........................................................ C0. 3 v to 2.8 v reference short - circuit duration ..................... ind efinite operating temperature range ltc 29 83 c ................................................. 0o c to 70o c ltc 29 83 i ............................................. C40 o c to 85o c (notes 1, 2) o r d er i n f or m a t ion lead free finish tape and reel part marking* package description temperature range LTC2983clx#pbf LTC2983clx#trpbf LTC2983 48-lead (7mm 7mm) lqfp 0c to 70c LTC2983ilx#pbf LTC2983ilx#trpbf LTC2983 48-lead (7mm 7mm) lqfp C40c to 85c consult lt c marketing for parts specified with wider operating temperature ranges. *the temperature grade is identified by a label on the shipping container. for more information on lead free part marking, go to: http://www.linear.com/leadfree/ for more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ 13 14 15 16 17 18 19 20 21 22 23 24 48 47 46 45 44 43 42 41 40 39 38 37 v refout v refp gnd ch1 ch2 ch3 ch4 ch5 ch6 ch7 ch8 ch9 25 26 27 28 29 30 31 32 33 34 35 36 ch10 ch11 ch12 ch13 ch14 ch15 ch16 ch17 ch18 ch19 ch20 com 12 11 10 9 8 7 6 5 4 3 2 1 gnd v ref_byp nc gnd v dd gnd v dd gnd v dd gnd v dd gnd q1 q2 q3 v dd gnd ldo reset cs sdi sdo sck interrupt top view lx package 48-lead (7mm 7mm) plastic lqfp t jmax = 150c, ja = 57c/w c o m ple t e s ys t e m e lec t rical c harac t eris t ics parameter conditions min typ max units supply voltage l 2.85 5.25 v supply current l 15 20 ma sleep current l 25 60 a input range all analog input channels l C0.05 v cc C 0.3 v output rate two conversion cycle mode (notes 6, 9) l 150 164 170 ms output rate three conversion cycle mode (notes 6, 9) l 225 246 255 ms input common mode rejection 50hz/60hz (note 4) l 120 db input normal mode rejection 60hz (notes 4, 7) l 120 db the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c. ltc 2983 2983f
4 for more information www.linear.com/LTC2983 a d c e lec t rical c harac t eris t ics parameter conditions min typ max units resolution (no missing codes) Cf s v in + f s l 24 bits integral nonlinearity v in(cm) = 1.25v (note 15) l 2 30 ppm of v ref offset error l 0.5 2 v offset error drift (note 4) l 10 20 nv/c positive full-scale error (notes 3, 15) l 100 ppm of v ref positive full-scale drift (notes 3, 15) l 0.1 0.5 ppm of v ref /c input leakage l 1 na negative full-scale error (notes 3, 15) l 100 ppm of v ref negative full-scale drift (notes 3, 15) l 0.1 0.5 ppm of v ref /c output noise (note 5) l 0.8 1.5 v rms common mode input range l C0.05 v dd C 0.3 v rtd excitation current (note 16) l C25 table 30 25 % rtd excitation current matching continuously calibrated l error within noise level of adc thermistor excitation current (note 16) l C37.5 table 53 37.5 % the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c. r e f erence e lec t rical c harac t eris t ics parameter conditions min typ max units output voltage v refout (note 10) 2.49 2.51 v output voltage temperature coefficient i-grade l 3 10 ppm/c output voltage temperature coefficient c-grade l 3 20 ppm/c line regulation l 10 ppm/v load regulation i out(source) = 100a l 5 mv/ma i out(sink) = 100a l 5 mv/ma output voltage noise 0.1hz f 10hz 4 v p-p 10hz f 1khz 4.5 v p-p output short-circuit current short v refout to gnd 40 ma short v refout to v dd 30 ma turn-on time 0.1% setting, c load = 1f 115 s long term drift of output voltage (note 13) 60 ppm/khr hysteresis (note 14) ?t = 0c to 70c ?t = C40c to 85c 30 70 ppm ppm the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c. parameter conditions min typ max units input normal mode rejection 50hz (notes 4, 8) l 120 db input normal mode rejection 50hz/60hz (notes 4, 6, 9) l 75 db power-on reset threshold 2.25 v analog power-up (note 11) l 100 ms digital initialization (note 12) l 100 ms the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c. c o m ple t e s ys t e m e lec t rical c harac t eris t ics ltc 2983 2983f
5 for more information www.linear.com/LTC2983 digi t al i npu t s an d digi t al o u t pu t s symbol parameter conditions min typ max units external sck frequency range l 0 2 mhz external sck low period l 250 ns external sck high period l 250 ns t 1 cs to sdo valid l 0 200 ns t 2 cs to sdo hi-z l 0 200 ns t 3 cs to sck l 100 ns t 4 sck to sdo valid l 225 ns t 5 sdo hold after sck l 10 ns t 6 sdi setup before sck l 100 ns t 7 sdi hold after sck l 100 ns high level input voltage cs, sdi, sck, reset l v dd C 0.5 v low level input voltage cs, sdi, sck, reset l 0.5 v digital input current cs, sdi, sck, reset l C10 10 a digital input capacitance cs, sdi, sck, reset 10 pf low level output voltage ( sdo, interrupt ) i o = C800a l 0.4 v high level output voltage ( sdo, interrupt ) i o = 1.6ma l v dd C 0.5 v hi-z output leakage (sdo) l C10 10 a the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c. note 1: stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. exposure to any absolute maximum rating condition for extended periods may affect device reliability and lifetime. note 2: all voltage values are with respect to gnd. note 3: full scale adc error. measurements do not include reference error . note 4: guaranteed by design, not subject to test. note 5: the output noise includes the contribution of internal calibration operations. note 6: mux configuration delay = default 2ms note 7: global configuration set to 60hz rejection. note 8: global configuration set to 50hz rejection. note 9: global configuration default 50hz/60hz rejection. note 10: the exact value of v ref is stored in the LTC2983 and used for all measurement calculations. temperature coefficient is measured by dividing the maximum change in output voltage by the specified temperature range. note 11: analog power-up. command status register inaccessible during this time. note 12: digital initialization. begins at the conclusion of analog power- up. command status register is 0 80 at the beginning of digital initialization and 0 40 at the conclusion. note 13: long-term stability typically has a logarithmic characteristic and therefore, changes after 1000 hours tend to be much smaller than before that time. t otal drift in the second thousand hours is normally less than one third that of the first thousand hours with a continuing trend toward reduced drift with time. long-term stability will also be affected by differential stresses between the ic and the board material created during board assembly. note 14: hysteresis in output voltage is created by package stress that differs depending on whether the ic was previously at a higher or lower temperature. output voltage is always measured at 25c, but the ic is cycled to the hot or cold temperature limit before successive measurements. hysteresis measures the maximum output change for the averages of three hot or cold temperature cycles. for instruments that are stored at well controlled temperatures (within 20 or 30 degrees of operational temperature), it is usually not a dominant error sour ce. typical hysteresis is the worst-case of 25c to cold to 25c or 25c to hot to 25c, preconditioned by one thermal cycle. note 15: differential input range is v ref /2. note 16: rt d and thermistor measurements are made ratiometrically. as a result current source excitation variation does not affect absolute accuracy. choose an excitation current such that largest sensor or r sense resistance value, when driven by the nominal excitation current, will drop 1v or less. the extended adc input range will accommodate variation in excitation current and the ratiometric calculation will negate the absolute value of the excitation current. ltc 2983 2983f
6 for more information www.linear.com/LTC2983 type e thermocouple error and rms noise vs temperature type b thermocouple error and rms noise vs temperature rtd pt -1000 error and rms noise vs temperature type r thermocouple error and rms noise vs temperature type s thermocouple error and rms noise vs temperature type t thermocouple error and rms noise vs temperature typical p er f or m ance c harac t eris t ics type j thermocouple error and rms noise vs temperature type k thermocouple error and rms noise vs temperature type n thermocouple error and rms noise vs temperature thermocouple temperature (c) error/rms noise (c) 2983 g01 1.0 0.8 0.6 0.4 0.2 0 ?0.2 ?0.4 ?0.6 ?0.8 ?1.0 ?400 800 1200 1600 4000 rms noise error thermocouple temperature (c) error/rms noise (c) 2983 g02 1.0 0.8 0.6 0.4 0.2 0 ?0.2 ?0.4 ?0.6 ?0.8 ?1.0 ?400 800 1200 1600 4000 rms noise error thermocouple temperature (c) error/rms noise (c) 2983 g03 1.0 0.8 0.6 0.4 0.2 0 ?0.2 ?0.4 ?0.6 ?0.8 ?1.0 ?400 800 1200 1600 4000 rms noise error thermocouple temperature (c) error/rms noise (c) 2983 g04 1.0 0.8 0.6 0.4 0.2 0 ?0.2 ?0.4 ?0.6 ?0.8 ?1.0 ?400 800 1200 1600 2000 4000 rms noise error thermocouple temperature (c) error/rms noise (c) 2983 g05 1.0 0.8 0.6 0.4 0.2 0 ?0.2 ?0.4 ?0.6 ?0.8 ?1.0 ?400 800 1200 1600 2000 4000 rms noise error thermocouple temperature (c) error/rms noise (c) 2983 g06 1.0 0.8 0.6 0.4 0.2 0 ?0.2 ?0.4 ?0.6 ?0.8 ?1.0 ?400 200 400 600 0?200 rms noise error thermocouple temperature (c) error/rms noise (c) 2983 g07 1.0 0.8 0.6 0.4 0.2 0 ?0.2 ?0.4 ?0.6 ?0.8 ?1.0 ?400 400 800 1200 0 rms noise error thermocouple temperature (c) error/rms noise (c) 2983 g08 1.0 0.8 0.6 0.4 0.2 0 ?0.2 ?0.4 ?0.6 ?0.8 ?1.0 400 1200 1600 2000 800 rms noise error rtd temperature (c) error/rms noise (c) 2983 g09 1.0 0.8 0.6 0.4 0.2 0 ?0.2 ?0.4 ?0.6 ?0.8 ?1.0 ?400 400 800 0 rms noise error t ltc 2983 2983f
7 for more information www.linear.com/LTC2983 typical p er f or m ance c harac t eris t ics rtd pt -200 error and rms noise vs temperature rtd pt -100 error and rms noise vs temperature rtd ni-120 rtd error and rms noise vs temperature rtd temperature (c) error/rms noise (c) 2983 g10 1.0 0.8 0.6 0.4 0.2 0 ?0.2 ?0.4 ?0.6 ?0.8 ?1.0 ?400 400 800 0 rms noise error rtd temperature (c) error/rms noise (c) 2983 g11 1.0 0.8 0.6 0.4 0.2 0 ?0.2 ?0.4 ?0.6 ?0.8 ?1.0 ?400 0 200 400 600 800 1000 ?200 rms noise error rtd temperature (c) error/rms noise (c) 2983 g12 1.0 0.8 0.6 0.4 0.2 0 ?0.2 ?0.4 ?0.6 ?0.8 ?1.0 ?100 0 100 200 300 rms noise error 5k thermistor error vs temperature 10 k thermistor error vs temperature 3k thermistor error vs temperature 30k thermistor error vs temperature ysi-400 thermistor error vs temperature thermistor temperature (c) error (c) 2983 g19 1.0 0.8 0.6 0.2 0.4 ?1.0 ?0.8 ?0.6 ?0.4 ?0.2 0 ?40 0?20 20 80 100 6040 120 140 thermistor temperature (c) error (c) 2983 g20 1.0 0.8 0.6 0.2 0.4 ?1.0 ?0.8 ?0.6 ?0.4 ?0.2 0 ?40 0?20 20 80 100 6040 120 140 thermistor temperature (c) error (c) 2983 g21 1.0 0.8 0.6 0.2 0.4 ?1.0 ?0.8 ?0.6 ?0.4 ?0.2 0 ?40 0?20 20 80 100 6040 120 140 thermistor temperature (c) error (c) 2983 g22 1.0 0.8 0.6 0.2 0.4 ?1.0 ?0.8 ?0.6 ?0.4 ?0.2 0 ?40 0?20 20 80 100 6040 120 140 thermistor temperature (c) error (c) 2983 g23 1.0 0.8 0.6 0.2 0.4 ?1.0 ?0.8 ?0.6 ?0.4 ?0.2 0 ?40 0?20 20 80 100 6040 120 140 thermistor temperature (c) error (c) 2983 g24 1.0 0.8 0.6 0.2 0.4 ?1.0 ?0.8 ?0.6 ?0.4 ?0.2 0 ?40 0?20 20 80 100 6040 120 140 2.252k thermistor error vs temperature ltc 2983 2983f
8 for more information www.linear.com/LTC2983 typical p er f or m ance c harac t eris t ics adjacent channel offset error vs input fault voltage ( v cc = 5v) adjacent channel offset error vs input fault voltage ch1 fault voltage (v) ch2 offset error (v) 2983 g25 2.5 1.5 2.0 ?0.5 0 0.5 1.0 4.95 5.055 5.1 5.2 5.25 5.15 5.3 5.35 ch1 fault voltage (v) ch2 offset error (v) 2983 g26 2.5 1.5 2.0 ?0.5 0 0.5 1.0 0 ?0.05 ?0.1 ?0.2 ?0.25 ?0.15 ?0.3 ?0.35 offset vs temperature noise vs temperature i sleep vs temperature one shot conversion current vs temperature v refout vs temperature LTC2983 temperature (c) offset (v) 2983 g13 2.0 1.5 1.0 0.5 0 ?0.5 ?1.0 ?1.5 ?2.0 ?50 ?25 50 75 250 100 125 v cc = 5.25v v cc = 4.1v v cc = 2.85v LTC2983 temperature (c) noise (v rms ) 2983 g14 1.2 1.0 0.8 0.6 0.4 0.2 0 ?50 50 0 25 ?25 10075 125 v cc = 5.25v v cc = 4.1v v cc = 2.85v LTC2983 temperature (c) i sleep (a) 2983 g15 60 50 40 30 20 10 0 ?50 ?25 50 75 250 100 125 v cc = 5.25v v cc = 4.1v v cc = 2.85v LTC2983 temperature (c) i idle (ma) 2983 g16 16.0 15.8 15.6 15.4 15.2 14.8 14.6 14.4 14.2 15.0 0 ?50 50250?25 10075 125 v cc = 5.25v v cc = 4.1v v cc = 2.85v LTC2983 temperature (c) v ref(out) (v) 2983 g28 2.5005 2.50025 2.49975 2.5 2.4995 ?60 ?40 ?20 40 60 80 200 100 120 input voltage (v) input leakage (na) 2983 g18 1.0 0.8 0.9 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0 1 2 43 5 6 ?45c 25c 90c channel input leakage current vs temperature diode error and repeatability vs temperature diode temperature (c) error (c) 2983 g27 1.0 0.8 0.6 ?0.2 ?0.4 ?0.6 ?0.8 0 0.2 0.4 ?1.0 ?40 20 80 140 ltc 2983 2983f
9 for more information www.linear.com/LTC2983 p in func t ions gnd (pins 1, 3, 5, 7, 9, 12, 15, 44): ground. connect each of these pins to a common ground plane through a low impedance connection. all eight pins must be grounded for proper operation. v dd (pins 2, 4, 6, 8, 45): analog power supply. tie all five pins together and bypass as close as possible to the device, to ground with a 0.1f capacitor. v ref_byp ( pin 11): internal reference power. this is an internal supply pin, do not load this pin with external circuitry. decouple with a 0.1f capacitor to gnd. v refout (pin 13): reference output voltage. short to v refp . a minimum 1 f capacitor to ground is required. do not load this pin with external circuitry. v refp (pin 14): positive reference input. tie to v refout . ch1 to ch 20 (pin 16 to pin 35): analog inputs. may be programmed for single-ended, differential, or ratiometric operation. the voltage on these pins can have any value between gnd C 50 mv and v dd C 0.3 v. unused pins can be grounded or left floating. com (pin 36): analog input. the common negative input for all single-ended configurations. the voltage on this pin can have any value between gnd C 50 mv and v dd C 0.3v. this pin is typically tied to ground for temperature measurements . interrup t (pin 37): this pin outputs a low when the device is busy either during start-up or while a conversion cycle is in progress. this pin goes high at the conclusion of the start-up state or conversion cycle. sck (pin 38): serial clock pin. data is shifted out of the device on the falling edge of sck and latched by the device on the rising edge. sdo ( pin 39): serial data out. during the data output state , this pin is used as the serial data output. when the chip select pin is high, the sdo pin is in a high impedance state. sdi ( pin 40): serial data input. used to program the device. data is latched on the rising edge of sck. cs (pin 41): active low chip select. a low on this pin enables the digital input / output. a high on this pin places sdo in a high impedance state. a falling edge on cs marks the beginning of a spi transaction and a rising edge marks the end. reset (pin 42): active low reset. while this pin is low, the device is forced into the reset state. once this pin is returned high, the device initiates its start-up sequence. ldo (pin 43): 2.5 v ldo output. bypass with a 10f capacitor to gnd. this is an internal supply pin, do not load this pin with external circuitry. q3, q2, q 1 (pins 46, 47, 48): external bypass pins for C200mv integrated charge pump. tie a 10 f x7r capaci - tor between q1 and q2 close to each pin. ti e a 10 f x5r capacitor from q3 to ground. these are internal supply pins, do not make additional connections. ltc 2983 2983f
10 for more information www.linear.com/LTC2983 b lock diagra m 2983 bd 21:6 mux ch1 to ch20 com adc1 rom ram adc2 interrupt sdo sck sdi cs reset adc3 excitation current sources 10ppm/c reference v refout v refp v ref_byp 0.1f v dd q 2 q 1 q 3 ldo processor ldo charge pump gnd 10f 10f 10f 1f ltc 2983 2983f
11 for more information www.linear.com/LTC2983 spi timing diagram tes t c ircui t s 2983 tc01 sdo 1.69k hi-z to v oh v ol to v oh v oh to hi-z c load = 20pf sdo 1.69k hi-z to v ol v oh to v ol v ol to hi-z c load = 20pf v dd ti m ing diagra m sck sdi 2983 td01 t 3 t 1 t 6 cs sdo t 7 t 2 t 4 t 5 ltc 2983 2983f
12 for more information www.linear.com/LTC2983 o verview the LTC2983 measures temperature using the most com- mon sensors ( thermocouples, rtds, thermistors, and diodes). it includes all necessary active circuitry, switches , measurement algorithms, and mathematical conversions to determine the temperature for each sensor type. thermocouples can measure temperatures from as low as C265 c to over 1800c . thermocouples generate a voltage as a function of the temperature difference between the tip (thermocouple temperature) and the electrical connection on the circuit board ( cold junction temperature). in order to determine the thermocouple temperature, an accurate measurement of the cold junction temperature is required; this is known as cold junction compensation. the cold junction temperature is usually determined by placing a separate ( non-thermocouple) temperature sensor at the cold junction. the LTC2983 allows diodes, rtds, and thermistors to be used as cold junction sensors. in order to convert the voltage output from the thermocouple into a temperature result, a high order polynomial equation (up to 14 th order) must be solved. the LTC2983 has these polynomials built in for virtually all standard thermocouples (j, k, n, e, r, s, t, and b). additionally, inverse polyno - mials must be solved for the cold junction temperature. the LTC2983 simultaneously measures the thermocouple output and the cold junction temperature and performs all required calculations to report the thermocouple tem - perature in c or f. it directly digitizes both positive and negative voltages ( down to 50 mv below ground) from a single ground referenced supply, includes sensor burn- out detection, and allows external protection/anti-aliasing circuits without the need of buffer circuits. diodes are convenient low cost sensor elements and are often used to measure cold junction temperatures in thermocouple applications. diodes are typically used to measure temperatures from C60 c to 130 c, which is suitable for most cold junction applications. diodes gen - erate an output voltage that is a function of temperature and excitation current. when the difference of two diode output voltages are taken at two different excitation current levels, the result ( ?v be ) is proportional to temperature. the LTC2983 accurately generates excitation currents, measures the diode voltages, and calculates the tempera - ture in c or f. rtds and thermistors are resistors that change value as a function of temperature. rtds can measure temperatures over a wide temperature range, from as low as C200 c to 850c while thermistors typically operate from C40c to 150c . in order to measure one of these devices a precision sense resistor is tied in series with the sensor. an excitation current is applied to the network and a ratiometric mea - surement is made. the value, in , of the rt d /thermistor can be determined from this ratio. this resistance is used to determine the temperature of the sensor element using a table lookup ( rtds) or solving steinhart-hart equations (thermistors). the LTC2983 automatically generates the excitation current, simultaneously measures the sense resistor and thermistor/ rtd voltage, calculates the sensor resistance and reports the result in c. the LTC2983 can digitize most rtd types (pt -10, pt -50, pt -100, pt -200, pt -500, pt -1000, and ni-120), has built in coefficients for many standards ( american, european, japanese, and its-90), and accommodates 2-wire, 3- wire, and 4-wire configurations. it also includes coefficients for calculating the temperature of standard 2.252k, 3k, 5k, 10k , and 30k thermistors. it can be configured to share one sense resistor among multiple rtds/thermistors and to rotate excitation current sources to remove parasitic thermal effects. ltc 2983 2983f
13 for more information www.linear.com/LTC2983 o verview table 1. LTC2983 error contribution and peak noise errors sensor type temperature range system accuracy peak-to-peak noise type k thermocouple C200c to 0c 0c to 1372c (t emperature ? 0.155% + 0.05)c (temperature ? 0.077% + 0.05)c 0.08c t ype j thermocouple C210c to 0c 0c to 1200c (t emperature ? 0.15% + 0.05)c (temperature ? 0.065% + 0.05)c 0.07c t ype e thermocouple C200c to 0c 0c to 1000c (t emperature ? 0.121% + 0.05)c (temperature ? 0.065% + 0.05)c 0.06c t ype n thermocouple C200c to 0c 0c to 1300c (t emperature ? 0.180% + 0.08)c (temperature ? 0.065% + 0.08)c 0.13c t ype r thermocouple 0c to 1768c (temperature ? 0.07% + 0.4)c 0.62c type s thermocouple 0c to 1768c (temperature ? 0.07% + 0.4)c 0.62c type b thermocouple 400c to 1820c (temperature ? 0.065%)c 0.83c type t thermocouple C250c to 0c 0c to 400c ( t emperature ? 0.10% + 0.05)c (temperature ? 0.065% + 0.05)c 0.09c external diode (2 reading) C40c to 85c 0.25c 0.05c external diode (3 reading) C40c to 85c 0.25c 0.2c platinum rtd - pt -10, r sense = 1k platinum rtd - pt -100, r sense = 2k platinum rtd - pt -500, r sense = 2k platinum rtd - pt -1000, r sense = 2k C200c to 800c C200c to 800c C200c to 800c C200c to 800c 0.1c 0.1c 0.1c 0.1c 0.05c 0.05c 0.02c 0.01c thermistor, r sense = 10k C40c to 85c 0.1c 0.01c table 1 shows the estimated system accuracy and noise associated with specific temperature sensing devices. system accuracy and peak-to-peak noise include the effects of the adc, internal amplifiers, excitation current sources, and integrated reference. accuracy and noise are the worst-case errors calculated from the guaranteed maximum adc and reference specifications. peak - to- peak noise values are calculated at 0c ( except type b was calculated at 400 c) and diode measurements use avg = on mode. thermocouple errors do not include the errors associated with the cold junction measurement . errors associated with a specific cold junction sensor within the operating temperature range can combined with the errors for a given thermocouple for total temperature measurement accuracy. ltc 2983 2983f
14 for more information www.linear.com/LTC2983 table 2a. memory map LTC2983 memory map segment start address end address size (bytes) description command status register 0x000 0x000 1 see table 6, initiate conversion, sleep command reserved 0x001 0x00f 15 temperature result memory 20 words - 80 bytes 0 x010 0x05f 80 see tables 8 to 10, read result reserved 0x060 0x0ef 144 global configuration register 0x0f0 0x0f0 1 reserved 0x0f1 0x0f3 3 measure multiple channels bit mask 0x0f4 0x0f7 4 see tables 65, 66, run multiple conversions global status register 0x0f8 0x0f8 1 reserved 0x0f9 0x0fe 6 mux configuration delay 0x0ff 0x0ff 1 see mux configuration delay section of data sheet reserved 0x100 0x1ff 256 channel assignment data 0x200 0x24f 80 see tables 3, 4, channel assignment custom sensor table data 0x250 0x3cf 384 reserved 0x3d0 0x3ff 48 o verview memory map the LTC2983 channel assignment, configuration, conver- sion start , and results are all accessible via the ram (see t able 2 a). table 2 b details the valid spi instruction bytes for accessing memory. the channel conversion results are mapped into memory locations 0 x010 to 0 x05f and can be read using the spi interface as shown in figure 1. a read is initiated by sending the read instruction byte = 0 x03 followed by the address and then data. channel assign- ment data resides in memory locations 0 x200 to 0x24f and can be programmed via the spi interface as shown in figure 2. a write is initiated by sending the write instruc - tion byte = 0 x02 followed by the address and then data. conversions are initiated by writing the conversion control byte ( see table 6) into memory location 0x000 (command status register). table 2b. spi instruction byte instruction spi instruction byte description read 0b00000011 see figure 1 write 0b00000010 see figure 2 no opp 0bxxxxxx0x ltc 2983 2983f
15 for more information www.linear.com/LTC2983 o verview figure 2. memory write operation figure 1. memory read operation sck cs receiver samples data on rising edge transmitter transitions data on falling edge sdi i7 i6 i5 i4 i3 i2 i1 i0 0 0 0 0 0 0 1 1 a15 a14 a13 a12 a11 a10 a9 a8 16-bit address field user memory read transaction first data byte subsequent data bytes may follow spi instruction byte read = 0x03 a7 a6 a5 a4 a3 a2 a1 a0 sdo 2983 f01 d7 d6 d5 d4 d3 d2 d1 d0 ? ? ? ? ? ? sck cs receiver samples data on rising edge transmitter transitions data on falling edge sdi i7 i6 i5 i4 i3 i2 i1 i0 0 0 0 0 0 0 1 0 a15 a14 a13 a12 a11 a10 a9 a8 16-bit address field user memory write transaction first data byte subsequent data bytes may follow spi instruction byte write = 0x02 a7 a6 a5 a4 a3 a2 a1 a0 2983 f02 ? ? ? d7 d6 d5 d4 d3 d2 d1 d0 ? ? ? ltc 2983 2983f
16 for more information www.linear.com/LTC2983 a pplica t ions i n f or m a t ion the LTC2983 combines high accuracy with ease of use. the basic operation is simple and is composed of five states (see figure 3). applicable). the user is locked out of ram access while in the state ( except for reading status location 0x000). the end of conversion is indicated by both the inter - rupt pin going high and a status register start bit going low and done bit going high. 5. read results. in this state, the user has access to ram and can read the completed conversion results and fault status bits. it is also possible for the user to modify/append the channel assignment data during the read results state. conversion state details state 1: start-up the start-up state automatically occurs when power is ap- plied to the LTC2983. if the power drops below a threshold of 2.6 v and then returns to the normal operating voltage (2.85 v to 5.25v ), the LTC2983 resets and enters the power- up state. note that the LTC2983 also enters the start-up state at the conclusion of the sleep state. the start-up state can also be entered at any time during normal operation by pulsing the reset pin low. in the first phase of the start-up state all critical analog cir cuits are powered up. this includes the ldo, reference, charge pump and adcs. during this first phase, the com- mand status register will be inaccessible to the user. this phase takes a maximum of 100 ms to complete. once this phase completes, the command status register will be accessible and return a value of 0 x80 until the LTC2983 is completely initialized. once the LTC2983 is initialized and ready to use, the interrupt pin will go high and the command status register will return a read value of 0x40 (start bit?=?0, done bit?=?1). at this point the LTC2983 is fully initialized and is ready to perform a conversion. state 2: channel assignment the LTC2983 ram can be programmed with up to 20 sets of 32-bit (4- byte) channel assignment data. these reside sequentially in ram with a one-to-one correspondence to each of the 20 analog input channels ( see table 3). channels that are not used should have their channel assignment data set to all zeros (default at start-up). the channel assignment data contains all the necessary information associated with the specific sensor tied to that channel ( see table 4). the first five bits determine the sensor type ( see table 5). associated with each sensor are sensor figure 3. basic operation 2983 f03 power-up, sleep or reset (optional) 200ms(max) no yes start-up channel assignment initiate conversion conversion read results status check complete? conversion states overview 1. start- up. after power is applied to the LTC2983 (v dd ?>?2.6v), there is a 200 ms wake up period. during this time, the ldo, charge pump, adcs, and reference are powered up and the internal ram is initialized. once start-up is complete, the interrupt pin goes high and the command status register will return a value of 0x40 (start bit?=?0, done bit?=?1) when read. 2. channel assignment. the device automatically enters the channel assignment state after start- up is complete. while in this state, the user writes sensor specific data for each input channel into ram. the assignment data contains information about the sensor type, pointers to cold junction sensors or sense resistors, and sensor specific parameters. 3. initiate conversion. a conversion is initiated by writing a measurement command into ram memory location 0x000. this command is a pointer to the channel in which the conversion will be performed. 4. conversion. a new conversion begins automatically following an initiate conversion command. in this state, the adc is running a conversion on the specified chan - nel and associated cold junction or r sense channel (if ltc 2983 2983f
17 for more information www.linear.com/LTC2983 table 3. channel assignment memory map channel assignment number configuration d ata start address configura tion d ata address + 1 configura tion d ata address + 2 configura tion d ata end address + 3 size (by tes) ch1 0x200 0x201 0x202 0x203 4 ch2 0x204 0x205 0x206 0x207 4 ch3 0x208 0x209 0x20a 0x20b 4 ch4 0x20c 0x20d 0x20e 0x20f 4 ch5 0x210 0x211 0x212 0x213 4 ch6 0x214 0x215 0x216 0x217 4 ch7 0x218 0x219 0x21a 0x21b 4 ch8 0x21c 0x21d 0x21e 0x21f 4 ch9 0x220 0x221 0x222 0x223 4 ch10 0x224 0x225 0x226 0x227 4 ch11 0x228 0x229 0x22a 0x22b 4 ch12 0x22c 0x22d 0x22e 0x22f 4 ch13 0x230 0x231 0x232 0x233 4 ch14 0x234 0x235 0x236 0x237 4 ch15 0x238 0x239 0x23a 0x23b 4 ch16 0x23c 0x23d 0x23e 0x23f 4 ch17 0x240 0x241 0x242 0x243 4 ch18 0x244 0x245 0x246 0x247 4 ch19 0x248 0x249 0x24a 0x24b 4 ch20 0x24c 0x24d 0x24e 0x24f 4 a pplica t ions i n f or m a t ion table 4. channel assignment data sensor type sensor specific configuration channel assignment memory location configuration data start address configuration data start address + 1 configuration data start address + 2 configuration data start address + 3 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 thermocouple type = 1 to 9 cold junction channel assignment [4:0] sgl=1 diff=0 oc check oc current [1:0] 0 0 0 0 0 0 custom address [5:0] custom length - 1 [5:0] rtd t ype = 10 to 18 r sense channel assignment [4:0] 2, 3, 4 wire excitation mode excitation current [3:0] standard [1:0] custom address [5:0] custom length - 1 [5:0] thermistor type = 19 to 27 r sense channel assignment [4:0] sgl =1 diff=0 excitation mode excitation current [3:0] 0 0 0 custom address [5:0] custom length - 1 [5:0] diode type = 28 sgl=1 diff=0 2 to 3 reading avg on current [1:0] ideality factor (2, 20) v alue from 0 to 4 with 1/1048576 resolution all zeros use factory set default in rom sense resistor type = 29 sense resistor value (17, 10) up to 131,072 with 1/1024 resolution direct adc type = 30 sgl=1 diff=0 not used disabled (default) type = 0, 31 not used ltc 2983 2983f
18 for more information www.linear.com/LTC2983 a pplica t ions i n f or m a t ion specific configurations. these include pointers to cold junction or sense resistor channels, pointers to memory locations of custom linearization data, sense resistor values and diode ideality factors. also included in this data are, if applicable, the excitation current level, single - ended/ differential input mode, as well as sensor specific controls. separate detailed opera - tion sections for thermocouples, rtds, diodes, thermistors , and sense resistors describe the assignment data associated with each sensor type in more detail. table 5. sensor type selection 31 30 29 28 27 sensor type 0 0 0 0 0 unassigned 0 0 0 0 1 type j thermocouple 0 0 0 1 0 type k thermocouple 0 0 0 1 1 type e thermocouple 0 0 1 0 0 type n thermocouple 0 0 1 0 1 type r thermocouple 0 0 1 1 0 type s thermocouple 0 0 1 1 1 type t thermocouple 0 1 0 0 0 type b thermocouple 0 1 0 0 1 custom thermocouple 0 1 0 1 0 rtd pt -10 0 1 0 1 1 rtd pt -50 0 1 1 0 0 rtd pt -100 0 1 1 0 1 rtd pt -200 0 1 1 1 0 rtd pt -500 0 1 1 1 1 rtd pt -1000 1 0 0 0 0 rtd 1000 (0.00375) 1 0 0 0 1 rtd ni-120 1 0 0 1 0 rtd custom 1 0 0 1 1 thermistor 44004/44033 2.252k at 25c 1 0 1 0 0 thermistor 44005/44030 3k at 25c 1 0 1 0 1 thermistor 44007/44034 5k at 25c 1 0 1 1 0 thermistor 44006/44031 10k at 25c 1 0 1 1 1 thermistor 44008/44032 30k at 25c 1 1 0 0 0 thermistor ysi 400 2.252k at 25c 1 1 0 0 1 thermistor spectrum 1003k 1k 1 1 0 1 0 thermistor custom steinhart-hart 1 1 0 1 1 thermistor custom table 1 1 1 0 0 diode 1 1 1 0 1 sense resistor 1 1 1 1 0 direct adc 1 1 1 1 1 reserved table 7. input channel mapping b7 b6 b5 b4 b3 b2 b1 b0 channel selected 1 0 0 0 0 0 0 0 multiple channels 1 0 0 0 0 0 0 1 ch1 1 0 0 0 0 0 1 0 ch2 1 0 0 0 0 0 1 1 ch3 1 0 0 0 0 1 0 0 ch4 1 0 0 0 0 1 0 1 ch5 1 0 0 0 0 1 1 0 ch6 1 0 0 0 0 1 1 1 ch7 1 0 0 0 1 0 0 0 ch8 1 0 0 0 1 0 0 1 ch9 1 0 0 0 1 0 1 0 ch10 1 0 0 0 1 0 1 1 ch11 1 0 0 0 1 1 0 0 ch12 1 0 0 0 1 1 0 1 ch13 1 0 0 0 1 1 1 0 ch14 1 0 0 0 1 1 1 1 ch15 1 0 0 1 0 0 0 0 ch16 1 0 0 1 0 0 0 1 ch17 1 0 0 1 0 0 1 0 ch18 1 0 0 1 0 0 1 1 ch19 1 0 0 1 0 1 0 0 ch20 1 0 0 1 0 1 1 1 sleep all other combinations reserved table 6. command status register b7 b6 b5 b4 b3 b2 b1 b0 start = 1 done = 0 0 channel selection 1 to 20 start conversion 1 0 0 1 0 1 1 1 initiate sleep state 3: initiate conversion once the channel assignment is complete, the device is ready to begin a conversion. a conversion is initiated by writing start ( b7?=?1) and done ( b6?=?0) followed by the desired input channel (b4 C b0) into ram memory loca - tion 0x000 ( see t ables 6 and 7). it is possible to initiate a measurement cycle on multiple channels by setting the channel selection bits ( b 4 to b 0) to 00000; see the running conversions consecutively on multiple channels section of the data sheet. bits b 4 to b 0 determine which input channel the conversion is performed upon and are simply the binary equivalent of the channel number (see table 7). bit b5 should be set to 0. ltc 2983 2983f
19 for more information www.linear.com/LTC2983 a pplica t ions i n f or m a t ion bits b7 and b6 serve as start/done bits. in order to start a conversion, these bits must be set to 10 ( b7=1 and b6=0). when the conversion begins, the interrupt pin goes low. once the conversion is complete, bits b7 and b6 will toggle to 01 ( b7=0 and b6=1) (address = 0x000) and the interrupt pin will go high, indicating the conversion is complete and the result is available. state 4: conversion the measurement cycle starts after the initiate conversion command is written into ram location 0x000 ( table 6). the LTC2983 simultaneously measures the selected input sensor, sense resistors ( rtds and thermistors), and cold junction temperatures if applicable (thermocouples). once the conversion is started, the user is locked out of the ram, with the exception of reading status data stored in ram memory location 0x000. once the conversion is started the interrupt pin goes low. depending on the sensor configuration, two or three 82ms cycles are required per temperature result. these correspond to conversion rates of 167 ms and 251ms, respectively. details describing these modes are described in the 2- and 3- cycle conversion modes section of the data sheet. the end of conversion can be monitored either through the interrupt pin ( low to high transition), or by reading the conversion control register in ram memory location 0x000 ( start bit, b7, toggles from 1 to 0 and done bit, b6, toggles from 0 to 1). state 5: read results once the conversion is complete, the conversion results can be read from ram memory locations corresponding to the input channel (see table 8). the conversion result is 32 bits long and contains both the sensor temperature ( d23 to d0) and sensor fault data (d31 to d24) (see tables 9a and 9b). the result is reported in c for all temperature sensors with a range of C273.16 c to 8192 c and 1/1024 c resolution or in f with a range of C459.67 f to 8192 f with 1/1024f table 8. conversion result memory map conversion channel st ar t address end address size (bytes) ch1 0x010 0x013 4 ch2 0x014 0x017 4 ch3 0x018 0x01b 4 ch4 0x01c 0x01f 4 ch5 0x020 0x023 4 ch6 0x024 0x027 4 ch7 0x028 0x02b 4 ch8 0x02c 0x02f 4 ch9 0x030 0x033 4 ch10 0x034 0x037 4 ch11 0x038 0x03b 4 ch12 0x03c 0x03f 4 ch13 0x040 0x043 4 ch14 0x044 0x047 4 ch15 0x048 0x04b 4 ch16 0x04c 0x04f 4 ch17 0x050 0x053 4 ch18 0x054 0x057 4 ch19 0x058 0x05b 4 ch20 0x05c 0x05f 4 resolution. included with the conversion result are seven sensor fault bits. these bits are set to a 1 if there was a prob - lem associated with the corresponding conversion result (see t able 10). tw o types of errors are reported: hard errors and soft errors. hard errors indicate the reading is invalid and the resulting temperature reported is C999c or f. soft errors indicate operation beyond the normal temperature range of the sensor or the input range of the adc. in this case, the calculated temperature is reported but the accuracy may be compromised. details relating to each fault type are sensor specific and are described in detail in the sensor specific sections of this data sheet. bit d24 is the valid bit and will be set to a 1 for valid data. once the data read is complete, the device is ready for a new initiate conversion command. in cases where new channel configuration data is required, the user has access to the ram in order to modify existing channel assignment data. ltc 2983 2983f
20 for more information www.linear.com/LTC2983 table 9a. example data output words (c) start address start address + 1 start address + 2 start address + 3 ( end address ) d 31 d 30 d 29 d 28 d 27 d 26 d 25 d 24 d 23 d 22 d 21 d 20 d 19 d 18 d 17 d 16 d 15 d 14 d 13 d 12 d 11 d 10 d9 d8 d7 d6 d5 d4 d3 d2 d1 d0 fault data sign msb lsb temperature sensor hard fault adc hard fault cj hard fault cj soft fault sensor over range fault sensor under range fault adc out of range fault v alid if 1 4096 c 1c 1/1024c 8192c 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1024c 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1c 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1/1024c 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0c 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 C1/1024c 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 C1c 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 C273.15c 1 1 1 1 1 1 0 1 1 1 0 1 1 1 0 1 1 0 1 1 0 0 1 1 1 table 9b. example data output words (f) start address start address + 1 start address + 2 start address + 3 ( end address ) d 31 d 30 d 29 d 28 d 27 d 26 d 25 d 24 d 23 d 22 d 21 d 20 d 19 d 18 d 17 d 16 d 15 d 14 d 13 d 12 d 11 d 10 d9 d8 d7 d6 d5 d4 d3 d2 d1 d0 fault data sign msb lsb temperature sensor hard fault adc hard fault cj hard fault cj soft fault sensor over range fault sensor under range fault adc out of range fault v alid if 1 4096 f 1f 1/1024f 8192f 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1024f 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1f 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1/1024f 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0f 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 C1/1024f 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 C1f 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 C459.67f 1 1 1 1 1 1 0 0 0 1 1 0 1 0 0 0 1 0 1 0 1 0 0 1 0 table 10. sensor fault reporting bit fault error type description output result d31 sensor hard fault hard bad sensor reading C999c or f d30 hard adc-out-of-range hard bad adc reading (could be large external noise event) C999c or f d29 cj hard fault hard cold junction sensor has a hard fault error C999c or f d28 cj soft fault soft cold junction sensor result is beyond normal range suspect reading d27 sensor over range soft sensor reading is above normal range suspect reading d26 sensor under range soft sensor reading is below normal range suspect reading d25 adc out-of-range soft adc absolute input voltage is beyond 1.125 ? v ref /2 suspect reading d24 valid na result valid (should be 1) discard results if 0 suspect reading a pplica t ions i n f or m a t ion ltc 2983 2983f
21 for more information www.linear.com/LTC2983 table 13. cold junction channel pointer (2) cold junction channel pointer b26 b25 b24 b23 b22 cold junction channel 0 0 0 0 0 no cold junction compensation, 0 c used for calculations 0 0 0 0 1 ch1 0 0 0 1 0 ch2 0 0 0 1 1 ch3 0 0 1 0 0 ch4 0 0 1 0 1 ch5 0 0 1 1 0 ch6 0 0 1 1 1 ch7 0 1 0 0 0 ch8 0 1 0 0 1 ch9 0 1 0 1 0 ch10 0 1 0 1 1 ch11 0 1 1 0 0 ch12 0 1 1 0 1 ch13 0 1 1 1 0 ch14 0 1 1 1 1 ch15 1 0 0 0 0 ch16 1 0 0 0 1 ch17 1 0 0 1 0 ch18 1 0 0 1 1 ch19 1 0 1 0 0 ch20 all other combinations invalid t hermocouple m easurements table 12. thermocouple type (1) thermocouple type b31 b30 b29 b28 b27 thermocouple types 0 0 0 0 1 type j thermocouple 0 0 0 1 0 type k thermocouple 0 0 0 1 1 type e thermocouple 0 0 1 0 0 type n thermocouple 0 0 1 0 1 type r thermocouple 0 0 1 1 0 type s thermocouple 0 0 1 1 1 type t thermocouple 0 1 0 0 0 type b thermocouple 0 1 0 0 1 custom thermocouple table 11. thermocouple channel assignment word (1) thermocouple type (2) cold junction channel pointer (3) sensor configuration (4) custom thermocouple d ata pointer t ables 4, 12 table 13 table 14 tables 67 to 69 measurement type 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 thermocouple types 1 to 9 cold junction channel assignment [4:0] sgl =1 diff=0 oc check oc current [1:0] 0 0 0 0 0 0 custom address [5:0] custom length [5:0] a pplica t ions i n f or m a t ion sensor is assigned to ( see table 13). when a conversion is performed on a channel tied to a thermocouple, the cold junction sensor is simultaneously and automatically measured. the final output data uses the embedded coef - ficients stored in rom to automatically compensate the cold junction temperature and output the thermocouple sensor temperature. channel assignment C thermocouples for each thermocouple tied to the LTC2983, a 32-bit channel assignment word is programmed into a memory location corresponding to the channel the sensor is tied to (see table 11). this word includes (1) thermocouple type, (2) cold junction channel pointer , (3) sensor configuration, and (4) custom thermocouple data pointer. (1) thermocouple type the thermocouple type is determined by the first five in - put bits b31 to b27 as shown in table 12. standard nist coefficients for types j,k,e,n,r,s,t and b thermocouples are stored in the device rom. if custom thermocouples are used, the custom thermocouple sensor type can be selected. in this case, user-specific data can be stored in the on-chip ram starting at the address defined in the custom thermocouple data pointer. (2) cold junction channel pointer the cold junction compensation can be a diode, rtd , or thermistor. the cold junction channel pointer tells the LTC2983 which channel (1 to 20) the cold junction ltc 2983 2983f
22 for more information www.linear.com/LTC2983 table 14. sensor configuration (3) sensor configuration sgl oc check oc current single-ended/ differential open-circuit current b21 b20 b19 b18 0 0 x x differential external 0 1 0 0 differential 10a 0 1 0 1 differential 100a 0 1 1 0 differential 500a 0 1 1 1 differential 1ma 1 0 x x single-ended external 1 1 0 0 single-ended 10a 1 1 0 1 single-ended 100a 1 1 1 0 single-ended 500a 1 1 1 1 single-ended 1ma a pplica t ions i n f or m a t ion (3) sensor configuration the sensor configuration field ( see table 14) is used to select single-ended ( b21=1) or differential (b21=0) input and allows selection of open circuit current if internal open- circuit detect is enabled ( bit b 20). single - ended readings are measured relative to the com pin and differential are measured between the selected ch tc and adjacent ch tc-1 ( see figure 4). if open -circuit detection is enabled, b20=1, then the user can select the pulsed current value applied during open- circuit detect using bits b18 and b 19 . the user determines the value of the open circuit current based on the size of the external protection resistor and filter capacitor ( typically 10a). this network needs to settle within 50 ms to 1v or less. the duration of the current pulse is approximately 8ms and occurs 50 ms before the normal conversion cycle. thermocouple channel assignments follow the general convention shown in figure 4. the thermocouple positive terminal ties to ch tc ( where tc is the selected channel number) for both the single-ended and differential modes of operation. for single-ended measurements the thermo - couple negative terminal and the com pin are grounded. the thermocouple negative terminal is tied to ch tc-1 for differential measurements. this node can either be grounded or tied to a bias voltage. (4) custom thermocouple data pointer see custom thermocouples section near the end of this data sheet for more information. figure 4. thermocouple channel assignment convention single-ended + ? + ? = ch tc (1 tc 20) com ch tc 0.1f channel assignment differential 2983 f04 = ch tc (2 tc 20) ch tc ch tc-1 0.1f channel assignment ltc 2983 2983f
23 for more information www.linear.com/LTC2983 table 15. thermocouple fault reporting bit fault error type description output result d31 sensor hard fault hard open circuit or hard adc or hard cj C999c or f d30 hard adc-out-of-range hard bad adc reading (could be large external noise event) C999c or f d29 cj hard fault hard cold junction sensor has a hard fault error C999c or f d28 cj soft fault soft cold junction sensor result is beyond normal range suspect reading d27 sensor over range soft thermocouple reading greater than high limit suspect reading d26 sensor under range soft thermocouple reading less than low limit suspect reading d25 adc out-of-range soft adc absolute input voltage is beyond 1.125 ? v ref /2 suspect reading d24 valid na result valid (should be 1) discard results if 0 valid reading a pplica t ions i n f or m a t ion fault reporting C thermocouple each sensor type has a unique fault reporting mechanism indicated in the upper byte of the data output word. table 15 shows faults reported in the measurement of thermo- couples. bit d 31 indicates the thermocouple sensor is open ( broken or not plugged in), the cold junction sensor has a hard fault, or the adc is out of range. this is indicated by a reading well beyond the normal operating range. bit d30 indicates a bad adc reading. this can be a result of either a broken ( open) sensor or an excessive noise event (esd or static discharge into the sensor path). either of these are a hard error and C999 c or f is reported. in the case of an excessive noise event, the device should recover and the following conversions will be valid if the noise event was a random, infrequent event. bit d29 indicates a hard fault occurred at the cold junction sensor and C999 c or f is reported. refer to the specific sensor (diode, themistor, or rtd) used for cold junction compensation. bit d28 indicates a soft fault occurred at the cold junction sensor. a valid temperature is reported, but the accuracy may be compromised since the cold junction sensor is operating outside its normal temperature range. bits d27 and d26 indicate over or under temperature limits have been exceeded for specific thermocouple types, as defined in table 16. bit d25 indicates the absolute voltage measured by the adc is beyond its normal operating range. this fault reflects a reading that is well beyond the normal range of a thermocouple. table 16. thermocouple temperature limits thermocouple type low temp limit c high temp limit c j-type C210 1200 k-type C265 1372 e-type C265 1000 n-type C265 1300 r-type C50 1768 s-type C50 1768 t-type C265 400 b-type 40 1820 custom lowest table entry highest table entry ltc 2983 2983f
24 for more information www.linear.com/LTC2983 table 18. diode sensor selection (1) sensor type b 31 b 30 b 29 b 28 b 27 sensor type 1 1 1 0 0 diode table 19. diode excitation current selection (3) excitation current b23 b22 1i 4i 8i 0 0 10a 40a 80a 0 1 20a 80a 160a 1 0 40a 160a 320a 1 1 80a 320a 640a d iode m easurements table 20. programming diode ideality factor (4) diode ideality factor value b 21 b 20 b 19 b 18 b 17 b 16 b 15 b 14 b 13 b 12 b 11 b 10 b9 b8 b7 b6 b5 b4 b3 b2 b1 b0 example h 2 1 2 0 2 C1 2 C2 2 C3 2 C4 2 C5 2 C6 2 C7 2 C8 2 C9 2 C10 2 C11 2 C12 2 C13 2 C14 2 C15 2 C16 2 C17 2 C18 2 C19 2 C20 1.25 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.003 (default) 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.006 0 1 0 0 0 0 0 0 0 1 1 0 0 0 1 0 0 1 0 0 1 1 bit b 24 enables a running average of the diode temperature reading. this reduces the noise when the diode is used as a cold junction temperature element on an isothermal block where temperatures change slowly. the algorithm used for diode averaging is a simple recursive running average. the new value is equal to the average of the current reading plus the previous value. new value = current reading 2 + previous value 2 if the current reading is 2 c above or below the previous value, the new value is reset to the current reading. (3) excitation current the next field in the channel assignment word ( b 23 to b 22) controls the magnitude of the excitation current applied to the diode ( see table 19). in the two conversion cycle mode, the device performs the first conversion at a current equal to 8 x the excitation current 1i . the second conversion occurs at 1i . alternatively, in the three conversion cycle mode the first conversion excitation current is 8i , the second is 4i and the 3 rd is 1i . a pplica t ions i n f or m a t ion (2) sensor configuration the sensor configuration field ( bits b26 to b24) is used to define various diode measurement properties. configura - tion bit b26 is set high for single-ended (measurement relative to com) and low for differential. bit b25 sets the measurement algorithm. if b25 is low, two conversion cycles ( one at 1i and one at 8i current excitation) are used to measure the diode. this is used in applications where parasitic resistance between the LTC2983 and the diode is small. parasitic resistance ef - fects can be removed by setting bit b25 high, enabling three conversion cycles ( one at 1i , one at 4i and one at 8i). table 17. diode channel assignment word (1) sensor type (2) sensor configuration (3) excitation current (4) diode ideality factor value table 18 table 19 table 20 measurement class 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 diode type = 28 sgl=1 diff=0 2 or 3 readings avg on current [1:0] non - ideality factor (2, 20) value from 0 to 4 with 1/1048576 resolution all zeros uses a factory set default of 1.003 channel assignment C diode for each diode tied to the LTC2983, a 32- bit channel as- signment word is programmed into a memory location corresponding to the channel the sensor is tied to (see table 17). this word includes (1) diode sensor selection, (2) sensor configuration , (3) excitation current, and (4) diode ideality factor. 1) sensor type the diode is selected by the first five input bits b31 to b27 (see table 18). ltc 2983 2983f
25 for more information www.linear.com/LTC2983 (4) diode ideality factor the last field in the channel assignment word ( b21 to b0) sets the diode ideality factor within the range 0 to 4 with 1/1048576 (2 C20 ) resolution. the top two bits ( b21 to b20) are the integer part and bits b19 to b0 are the fractional part of the ideality factor (see table 20). diode channel assignments follow the general convention shown in figure 5. the anode ties to ch d ( where d is the selected channel number) for both the single-ended and differential modes of operation, and the cathode is grounded. for differential diode measurements, the cathode is also tied to ch d-1 . fault reporting - diode each sensor type has unique fault reporting mechanism indicated in the upper byte of the data output word. table 21 shows faults reported in the measurement of diodes. bit d31 indicates the diode is open, shorted, not plugged in, wired backwards, or the adc reading is bad. any of these are hard faults and C999 c or f is reported. bit d30 indicates a bad adc reading. this can be a result of either a broken ( open) sensor or an excessive noise event (esd or static discharge into the sensor path). this is a a pplica t ions i n f or m a t ion figure 5. diode channel assignment convention hard error and C999 c or f is reported. in the case of an excessive noise event, the device should recover and the following conversions will be valid if the noise event was a random, infrequent event. bits d29 and d28 are not used for diodes. bits d27 and d26 indicate over or under temperature limits ( defined as t > 130 c or t < C60c ). the calculated temperature is reported, but the accuracy may be compromised. bit d25 indicates the absolute voltage measured by the adc is beyond its normal operating range. if a diode is used as the cold junction element, any hard or soft error is flagged in the corresponding thermocouple result (bits d28 and d29 in table 15). table 21. diode fault reporting bit fault error type description output result d31 sensor hard fault hard open, short, reversed, or hard adc C999c or f d30 hard adc-out-of-range hard bad adc reading (could be large external noise event) C999c or f d29 not used for diodes n/a always 0 d28 not used for diodes n/a always 0 d27 sensor over range soft t > 130c suspect reading d26 sensor under range soft t < C60c suspect reading d25 adc out-of-range soft adc absolute input voltage is beyond 1.125 ? v ref /2 suspect reading d24 valid na result valid (should be 1) discard results if 0 valid reading 2983 f05 single-ended = ch d (1 d 20) com ch d channel assignment differential = ch d (2 d 20) ch d ch d-1 channel assignment ltc 2983 2983f
26 for more information www.linear.com/LTC2983 example: single-ended type k and differential type t thermocouples with shared diode cold junction compensation f i gure 6 shows a typical temperature measurement system where two thermocouples share a single cold junction diode. in this example, a type k thermocouple is tied to ch1 and a type t thermocouple is tied to ch3 and ch4. they both share a single cold junction diode with ideality factor of h =1.003 tied to ch2. channel as - signment data for both thermocouples and the diode are a pplica t ions i n f or m a t ion shown in tables 22 to 24. thermocouple #1 ( type k) sensor type and configuration data are assigned to ch1. 32-bits of binary configuration data are mapped directly into memory locations 0 x200 to 0x203 ( see table 22). the cold junction diode sensor type and configuration data are assigned to ch 2. 32- bits of binary configuration data are mapped directly into memory locations 0x204 to 0x207 ( see table 23). thermocouple #2 ( type t) sen - sor type and configuration data are assigned to ch4. 32-bits of binary configuration data are mapped directly figure 6. dual thermocouple with diode cold junction example type k 0.1f type t = 1.003 2983 f06 type k thermocouple assigned to ch 1 (ch tc=1 ) diode cold junction assigned to ch 2 (ch d=2 ) type t thermocouple junction assigned to ch 4 (ch tc=4 ) ch4 ch3 ch2 ch1 0.1f com channel assignment memory locations 0x200 to 0x203 result memory locations 0x010 to 0x013 channel assignment memory locations 0x204 to 0x207 result memory locations 0x014 to 0x017 channel assignment memory locations 0x20c to 0x20f result memory locations 0x01c to 0x01f ltc 2983 2983f
27 for more information www.linear.com/LTC2983 table 22. thermocouple #1 channel assignment (type k, cold junction ch 2 , single-ended, 10a open-circuit detect) configuration field description # bits binary d ata memory address 0 x 200 memor y address 0 x 201 memory address 0 x 202 memory address 0 x 203 (1) thermocouple type t ype k 5 00010 0 0 0 1 0 (2) cold junction channel pointer ch 2 5 00010 0 0 0 1 0 (3) sensor configuration single-ended, 10a open-circuit 4 1100 1 1 0 0 not used set these bits to 0 6 000000 0 0 0 0 0 0 (4) custom thermocouple data pointer not custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0 table 23. diode channel assignment (single-ended 3-reading, averaging on, 20a/80a excitation, ideality factor = 1.003)) configuration field description # bits binary d ata memory address 0 x 204 memor y address 0 x 205 memory address 0 x 206 memory address 0 x 207 (1) sensor t ype diode 5 11100 1 1 1 0 0 (2) sensor configuration single-ended, 3-reading, average on 3 111 1 1 1 (3) excitation current 20a, 80a, 160a 2 01 0 1 (4) ideality factor 1.003 22 0100000000110001001001 0 1 0 0 0 0 0 0 0 0 1 1 0 0 0 1 0 0 1 0 0 1 table 24. thermocouple #2 channel assignment (type t, cold junction ch 2 , differential, 100a open-circuit detect) configuration field description # bits binary d ata memory address 0 x 20 c memor y address 0 x 20d memor y address 0 x 20e memor y address 0 x 20f (1) thermocouple t ype type t 5 00111 0 0 1 1 1 (2) cold junction channel pointer ch 2 5 00010 0 0 0 1 0 (3) sensor configuration differential, 100a open- circuit current 4 0101 0 1 0 1 not used set these bits to 0 6 000000 0 0 0 0 0 0 (4) custom thermocouple data pointer not custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0 a pplica t ions i n f or m a t ion into memory locations 0x20c to 0x20f (see table?24). a conversion is initiated on ch1 by writing 10000001 into memory location 0 x000. both the type k thermocouple and the diode are measured simultaneously. the LTC2983 calculates the cold junction compensation and determines the temperature of the type k thermocouple. once the conversion is complete, the interrupt pin goes high and memory location 0 x 000 becomes 01000001. similarly, a conversion can be initiated on ch4 by writing 10000100 into memory location 0 x000. the results (in c) can be read from memory locations 0 x010 to 0 x013 for ch1 and 0x01c to 0x01f for ch4. ltc 2983 2983f
28 for more information www.linear.com/LTC2983 a pplica t ions i n f or m a t ion rtd m easurements (2) sense resistor channel pointer rt d measurements are performed ratiometrically relative to a known r sense resistor. the sense resistor channel pointer field indicates the differential channel the sense resistor is tied to for the rtd ( see table 27). sense resis - tors are always measured differentially. table 26. rtd type (1) rtd type b31 b30 b29 b28 b27 rtd type 0 1 0 1 0 rtd pt -10 0 1 0 1 1 rtd pt -50 0 1 1 0 0 rtd pt -100 0 1 1 0 1 rtd pt -200 0 1 1 1 0 rtd pt -500 0 1 1 1 1 rtd pt -1000 1 0 0 0 0 rtd 1000 (=0.00375) 1 0 0 0 1 rtd ni-120 1 0 0 1 0 rtd custom table 25. rtd channel assignment word (1) rtd type (2) sense resistor channel pointer (3) sensor configuration (4) excitation current (5) rtd standard (6) custom rt d d ata pointer table 26 table 27 table 28 table 29 table 30 tables 72 to 74 measurement class 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 rtd type = 10 to 18 r sense channel assignment [4:0] 2, 3, 4 wire excitation mode excitation current [3:0] standard [1:0] custom address [5:0] custom length [5:0] table 27. sense resistor channel pointer (2) sense resistor channel pointer b26 b25 b24 b23 b22 sense resistor channel 0 0 0 0 0 invalid 0 0 0 0 1 invalid 0 0 0 1 0 ch2-ch1 0 0 0 1 1 ch3-ch2 0 0 1 0 0 ch4-ch3 0 0 1 0 1 ch5-ch4 0 0 1 1 0 ch6-ch5 0 0 1 1 1 ch7-ch6 0 1 0 0 0 ch8-ch7 0 1 0 0 1 ch9-ch8 0 1 0 1 0 ch10-ch9 0 1 0 1 1 ch11-ch10 0 1 1 0 0 ch12-ch11 0 1 1 0 1 ch13-ch12 0 1 1 1 0 ch14-ch13 0 1 1 1 1 ch15 -ch14 1 0 0 0 0 ch16-ch15 1 0 0 0 1 ch17-ch16 1 0 0 1 0 ch18-ch17 1 0 0 1 1 ch19-ch18 1 0 1 0 0 ch20-ch19 all other combinations invalid channel assignment C rtd for each rtd tied to the LTC2983, a 32- bit channel as- signment word is programmed into a memory location corresponding to the channel the sensor is tied to (see table 25). this word includes (1) rtd type , (2) sense resistor channel pointer , (3) sensor configuration, (4) excitation current , (5) rtd standard, and (6) custom rtd data pointer. (1) rtd type the rtd type is determined by the first five input bits b31 to b27 as shown in table 26. linearization coefficients for rtd types pt -10, pt -50, pt -100, pt -200, pt -500, pt -1000, and ni-120 with selectable common standards ( = 0.003850, = 0.003911, = 0.003916, and = 0.003926) are built into the device. if custom rtds are used, rtd custom can be selected. in this case, user specific data can be stored in the on-chip ram starting at the address defined by the custom rtd data pointers. ltc 2983 2983f
29 for more information www.linear.com/LTC2983 a pplica t ions i n f or m a t ion (3) sensor configuration the sensor configuration field is used to define various rtd properties. configuration bits b20 and b21 determine if the rtd is a 2, 3, or 4 wire type (see table 28). the simplest configuration is the 2- wire configuration. while this setup is simple, parasitic errors due to ir drops in the leads result in systematic temperature errors. the 3-wire configuration cancels rtd lead resistance errors (if the lines are equal resistance) by applying two matched current sources to the rtd , one per lead. mismatches in the two current sources are removed through transparent background calibration . 4- wire rtds remove unbalanced rtd lead resistance by measuring directly across the sensor using a high impedance kelvin sensing . 4-wire measurements with kelvin r sense are useful in applica- tions where sense resistor wiring parasitics can lead to errors; this is especially useful for low resistance pt -10 type rtds. in this case, both the rtd and sense resistor have kelvin sensing connections. the next sensor configuration bits ( b18 and b19) deter - mine the excitation current mode. these bits are used to enable r sense sharing, where one sense resistor is used for multiple 2-, 3-, and/or 4- wire rtds. in this case, the rtd ground connection is internal and each rt d points to the same r sense channel. table 28. rtd sensor configuration selection (3) sense configuration m easurement m ode b enefits number of wires excit a tion mode number of wires ground connection current source rot ation sense resistor sharing rtds possible per device cancels rt d matched lead resistance cancels rt d mismatch lead resistance cancels p arasitic thremocouple effects cancels r sense lead resistance b 21 b20 b19 b18 0 0 0 0 2-wire external no no 5 0 0 0 1 2-wire internal no yes 9 0 1 0 0 3-wire external no no 5 ? 0 1 0 1 3-wire internal no yes 9 ? 0 1 1 x reserved 1 0 0 0 4-wire external no no 4 ? ? 1 0 0 1 4-wire internal no yes 6 ? ? 1 0 1 0 4-wire internal yes yes 6 ? ? ? 1 0 1 1 reserved 1 1 0 0 4-wire, kelvin r sense external no no 3 ? ? ? 1 1 0 1 4-wire, kelvin r sense internal no yes 5 ? ? ? 1 1 1 0 4-wire, kelvin r sense internal yes yes 5 ? ? ? ? 1 1 1 1 reserved ltc 2983 2983f
30 for more information www.linear.com/LTC2983 a pplica t ions i n f or m a t ion table 29. total excitation current for all rtd wire types (4) excitation current b17 b16 b15 b14 current 0 0 0 0 external 0 0 0 1 5a 0 0 1 0 10a 0 0 1 1 25a 0 1 0 0 50a 0 1 0 1 100a 0 1 1 0 250a 0 1 1 1 500a 1 0 0 0 1ma bits b 18 and b 19 are also used to enable excitation current rotation to automatically remove parasitic thermocouple effects. parasitic thermocouple effects may arise from the physical connected between the rtd and the measure - ment instrument . this mode is available for all 4- wire configurations using internal current source excitation. (4) excitation current the next field in the channel assignment word ( b17 to b14) controls the magnitude of the excitation current applied to the rtd ( see table 29). the current selected is the total current flowing through the rtd independent of the wiring configuration. the r sense current is 2 x the sensor excitation current for 3-wire rtds. in order to prevent soft or hard faults, select a current such that the maximum voltage drop across the sensor or sense resistor is nominally 1.0 v. for example, if r sense is 10 k and the rtd is a pt -100, select an excitation current of 100 a for 2- wire and 4- wire rtds and select 50a for a 3- wire rtd . alternatively, using a 1 k sense resistor with a pt -100 rtd allows 500 a excitation for any wiring configuration. (5) rtd standard bits b13 and b12 set the rtd standard used and the corresponding callendar- van dusen constants (shown in table 30). (6) custom rtd data pointer in the case where an rtd not listed in table 30 is used, a custom rtd table may be entered into the LTC2983. see custom rtd section near the end of this data sheet for more information. table 30. rtd standards: rt = r0 ? (1 + a ? t + b ? t 2 + (t C 100c) ? c ? t 3 ) for t < 0c, rt = r0 ? (1 + a ? t + b ? t 2 ) for t > 0c (5) standard b13 b12 standard alpha a b c 0 0 european standard 0.00385 3.908300e-03 C5.775000e-07 C4.183000e-12 0 1 american 0.003911 3.969200e-03 C5.849500e-07 C4.232500e-12 1 0 japanese 0.003916 3.973900e-03 C5.870000e-07 C4.400000e-12 1 1 its-90 0.003926 3.984800e-03 C5.870000e-07 C4.000000e-12 x x rtd 1000-375 0.00375 3.810200e-03 C6.018880e-07 C6.000000e-12 x x *ni-120 n/a n/a n/a n/a *ni-120 uses table based data. ltc 2983 2983f
31 for more information www.linear.com/LTC2983 a pplica t ions i n f or m a t ion fault reporting C rtd each sensor type has unique fault reporting mechanism indicated in the most significant byte of the data output word. table 31 shows faults reported in the measurement of rtds. bit d 31 indicates the rtd or r sense is open, shorted, or not plugged in. this is a hard fault and C999 c or f is reported . bit d 30 indicates a bad adc reading. this can be a result of either a broken ( open) sensor or an excessive noise event ( esd or static discharge into the sensor path). this is a hard error and C999 c or f is reported. in the case of an excessive noise event, the device should recover and the following conversions will be valid if the noise was a random infrequent event. bits d29 and d28 are not used for rtds. bits d27 and d26 indicate over or under tem - perature limits ( see table 32). the calculated temperature is reported, but the accuracy may be compromised. bit d25 indicates the absolute voltage measured by the adc is beyond its normal operating range. if an rtd is used as the cold junction element, any hard or soft error is also flagged in the thermocouple result. table 32. voltage and resistance ranges rtd type min max low temp limit c high temp limit c pt -10 1.95 34.5 C200 850 pt -50 9.75 172.5 C200 850 pt -100 19.5 345 C200 850 pt -200 39 690 C200 850 pt -500 97.5 1725 C200 850 pt -1000 195 3450 C200 850 ni-120 66.6 380.3 C80 260 custom table lowest table entry highest table entry lowest table entry highest table entry table 31. rtd fault reporting bit fault error type description output result d31 sensor hard fault hard open or short rtd or r sense C999c or f d30 hard adc-out-of-range hard bad adc reading (could be large external noise event) C999c or f d29 not used for rtds n/a always 0 valid reading d28 not used for rtds n/a always 0 valid reading d27 sensor over range soft t > high temp limit (see table 32) suspect reading d26 sensor under range soft t < low temp limit (see table 32) suspect reading d25 adc out-of-range soft adc absolute input voltage is beyond 1.125 ? v ref /2 suspect reading d24 valid n/a result valid (should be 1) discard results if 0 valid reading ltc 2983 2983f
32 for more information www.linear.com/LTC2983 a pplica t ions i n f or m a t ion table 33. sense resistor channel assignment word (1) sensor type (2) sense resistor value () figure 36 figure 40 measurement class 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 sense resistor type = 29 sense resistor value (17, 10) up to 131,072 with 1/1024 resolution table 34. sense resistor selection (1) sensor type b31 b30 b29 b28 b27 sensor type 1 1 1 0 1 sense resistor table 35. example sense resistor values (2) sense resistor value () b 26 b 25 b 24 b 23 b 22 b 21 b 20 b 19 b 18 b 17 b 16 b 15 b 14 b 13 b 12 b 11 b 10 b9 b8 b7 b6 b5 b4 b3 b2 b1 b0 example r 2 16 2 15 2 14 2 13 2 12 2 11 2 10 2 9 2 8 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 2 C1 2 C2 2 C3 2 C4 2 C5 2 C6 2 C7 2 C8 2 C9 2 C10 10,000.2 0 0 0 1 0 0 1 1 1 0 0 0 1 0 0 0 0 0 0 1 1 0 0 1 1 0 1 99.99521k 1 1 0 0 0 0 1 1 0 1 0 0 1 1 0 1 1 0 0 1 1 0 1 0 1 1 1 1.0023k 0 0 0 0 0 0 0 1 1 1 1 1 0 1 0 1 0 0 1 0 0 1 1 0 0 1 1 sense resistor can be tied directly to 2-lead rt d elements. the disad- vantages of this topology are errors due to parasitic lead resistance. if sharing is not required (1 r sense per rtd ), then ch rtd should be grounded. the ground connection should be removed if sharing is enabled (1 r sense for multiple rtds). (2) sense resistor value the last field in the channel assignment word ( b26 to b0) sets the value of the sense resistor within the range 0 to 131,072 with 1/1024 precision ( see table 35). the top 17 bits (b26 to b10) create the integer and bits b9 to b0 create the fraction of the sense resistor value. example: 2-wire rtd the simplest rtd configuration is the 2- wire configura - tion, 2- wire r tds follow the general convention shown in figure 7. they require only two connections per rtd and sense resistor channel assignments follow the general convention shown in figure 8. the sense resistor is tied between ch rsense and ch rsense-1 , where ch rsense is tied to the 2 nd terminal of the rtd . channel assignment data ( see table 33) is mapped into a memory location corresponding to ch rsense . figure 7. 2-wire rtd channel assignment convention figure 8. sense resistor channel assignment convention for 2-wire rtds 2983 f07 optional gnd, remove for r sense sharing 2nd terminal ties to sense resistor (ch rsense ) 2 1 ch rtd-1 ch rtd excitation current flow = ch rtd (2 rtd 20) channel assignment 2983 f08 ch rsense-1 ch rsense r sense excitation current flow = ch rsense (2 rsense 20) channel assignment channel assignment for each sense resistor tied to the LTC2983, a 32-bit channel assignment word is programmed into a memory location corresponding to the channel the sensor is tied to ( see table 33). this word includes (1) sense resistor selection and (2) sense resistor value. (1) sensor type the sense resistor is selected by setting the first 5 input bits, b31 to b27, to 11101 (see table 34). ltc 2983 2983f
33 for more information www.linear.com/LTC2983 a pplica t ions i n f or m a t ion example: 2-wire rtds with shared r sense figure 9 shows a typical temperature measurement system using multiple 2- wire rtds. in this example, a pt -1000 rtd ties to ch17 and ch18 and an ni-120 rtd ties to ch19 and ch20. using this configuration, the LTC2983 can digitize up to nine 2- wire rtds with a single sense resistor. rtd #1 sensor type and configuration data are as - signed to ch 18 . 32 bits of binary configuration data are mapped directly into memory locations 0 x244 to 0 x247 (see t able 36). rtd #2 sensor type and configuration data are assigned to ch 20 . 32- bits of binary configuration data table 36. channel assignment data for 2-wire rtd #1 (pt -1000, r sense on ch 16 , 2-wire, shared r sense , 10a excitation current, = 0.003916 standard) configuration field description # bits binary d ata memory address 0 x 244 memor y address 0 x 245 memory address 0 x 246 memory address 0 x 247 (1) rt d type pt -1000 5 01111 0 1 1 1 1 (2) sense resistor channel pointer ch 16 5 10000 1 0 0 0 0 (3) sensor configuration 2-wire with shared r sense 4 0001 0 0 0 1 (4) excitation current 10a 4 0010 0 0 1 0 (5) standard japanese, = 0.003916 2 10 1 0 (6) custom rtd data pointer not custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0 are mapped directly into memory locations 0 x 24 c to 0 x 24 f (see t able 37). the sense resistor is assigned to ch 16 . the user-programmable value of this resistor is 5001.5. 32?bits of binary configuration data are mapped directly into memory locations 0x23c to 0x23f (see table 38). a conversion is initiated on ch 18 by writing 10010010 into memory location 0 x000. once the conversion is complete, the interrupt pin goes high and memory location 0x000 becomes 01010010. the resulting temperature in c can be read from memory locations 0 x054 to 0x057 (corresponding to ch 18 ). a conversion can be initiated and read from ch 20 in a similar fashion. figure 9. shared 2-wire rtd example r sense 5001.5 0.1f 2983 f09 0.1f sense resistor assigned to ch 16 (ch rsense=16 ) rtd #1 assigned to ch 18 (ch rtd=18 ) rtd #2 assigned to ch 20 (ch rtd=20 ) ch 20 ch 19 ch 16 ch 15 channel assignment memory locations 0x23c to 0x23f channel assignment memory locations 0x244 to 0x247 result memory locations 0x054 to 0x057 channel assignment memory locations 0x24c to 0x24f result memory locations 0x05c to 0x05f 0.1f 0.1f ch 17 ch 18 0.1f 0.1f 2-wire pt-1000 2-wire ni-120 2 1 2 1 ltc 2983 2983f
34 for more information www.linear.com/LTC2983 a pplica t ions i n f or m a t ion example: 3-wire rtd 3-wire rtd channel assignments follow the general con- vention shown in figure 10. terminals 1 and 2 tie to the input/excitation current sources and terminal 3 connects to the sense resistor. channel assignment data is mapped to memory locations corresponding to ch rtd . table 37. channel assignment data for 2-wire rtd #2 (ni-120, r sense on ch 16 , 2-wire, shared r sense , 100a excitation current) configuration field description # bits binary d ata memory address 0 x 24 c memor y address 0 x 24d memor y address 0 x 24e memor y address 0 x 24f (1) rtd type ni-120 5 10001 1 0 0 0 1 (2) sense resistor channel pointer ch 16 5 10000 1 0 0 0 0 (3) sensor configuration 2-wire with shared r sense 4 0001 0 0 0 1 (4) excitation current 100a 4 0101 0 1 0 1 (5) standard european = 0.00385 2 00 0 0 (6) custom rtd data pointer not custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0 table 38. channel assignment data for sense resistor (value = 5001.5) configuration field description # bits binary d ata memory address 0 x 23 c memor y address 0 x 23 d memor y address 0 x 23e memor y address 0 x 23f (1) sensor t ype sense resistor 5 11101 1 1 1 0 1 (2) sense resistor value 5001.5 27 000010011100010011000000000 0 0 0 0 1 0 0 1 1 1 0 0 0 1 0 0 1 1 0 0 0 0 0 0 0 0 0 sense resistor channel assignments follow the general convention shown in figure 11. the sense resistor is tied between ch rsense and ch rsense-1 , where ch rsense is tied to the 3 rd terminal of the rtd and ch rsense-1 is tied to ground ( or left floating for r sense sharing). channel assignment data ( see table 33) is mapped into the memory location corresponding to ch rsense . figure 10. 3-wire rtd channel assignment convention figure 11. 3-wire sense resistor channel assignment convention for 3-wire rtds 2983 f10 3rd terminal ties to sense resistor 2 3 1 ch rtd-1 ch rsense ch rtd excitation current flow = ch rtd (2 rtd 20) channel assignment 2983 f11 ch rsense-1 ch rsense r sense 2x excitation current flow = ch rsense (2 rsense 20) (optional gnd, remove for r sense sharing) channel assignment ltc 2983 2983f
35 for more information www.linear.com/LTC2983 table 39. channel assignment data for 3-wire rtd (pt-200, r sense on ch 7 , 3-wire, 50a excitation current, = 0.003911 standard) configuration field description # bits binary d ata memory address 0 x 220 memor y address 0 x 221 memory address 0 x 222 memory address 0 x 223 (1) rt d type pt -200 5 01101 0 1 1 0 1 (2) sense resistor channel pointer ch 7 5 00111 0 0 1 1 1 (3) sensor configuration 3-wire 4 0100 0 1 0 0 (4) excitation current 50a 4 0100 0 1 0 0 (5) standard american, = 0.003911 2 01 0 1 (6) custom rtd data pointer not custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0 table 40. channel assignment data for sense resistor (value = 12150.39) configuration field description # bits binary d ata memory address 0 x 218 memor y address 0 x 219 memory address 0 x 21a memor y address 0 x 21b (1) sensor t ype sense resistor 5 11101 1 1 1 0 1 (2) sense resistor value 12150.39 27 000101111011101100110001111 0 0 0 1 0 1 1 1 1 0 1 1 1 0 1 1 0 0 1 1 0 0 0 1 1 1 0 a pplica t ions i n f or m a t ion figure 12 shows a typical temperature measurement sys- tem using a 3-wire rt d . in this example, a 3-wire rtd s terminals tie to ch 9 , ch 8 , and ch 7 . the sense resistor ties to ch 7 and ch 6 . the sense resistor and rtd connect together at ch 7 . the 3-wire rtd reduces the errors associated with para- sitic lead resistance by applying excitation current to each rt d input. this first order cancellation removes matched lead resistance errors. this cancellation does not remove errors due to thermocouple effects or mismatched lead resistances. the rtd sensor type and configuration data are assigned to ch 9 . 32 bits of binary configuration data are mapped directly into memory locations 0 x 220 to 0 x 223 (see table 39). the sense resistor is assigned to ch 7 . the user-programmable value of this resistor is 12150.39. 32 bits of binary configuration data are mapped directly into memory locations 0x218 to 0x21b (see table 40). figure 12. 3-wire rtd example r sense 12,150.39 0.1f 2983 f12 0.1f r sense assigned to ch 7 (ch sense=7 ) 3-wire rtd assigned to ch 9 (ch rtd=9 ) ch 7 ch 6 channel assignment memory locations 0x218 to 0x21b channel assignment memory locations 0x220 to 0x223 result memory locations 0x030 to 0x033 0.1f 0.1f ch 8 ch 9 3-wire pt-200 2 3 1 ltc 2983 2983f
36 for more information www.linear.com/LTC2983 a pplica t ions i n f or m a t ion a conversion is initiated on ch 9 by writing 10001001 into memory location 0 x 000 . once the conversion is complete, the interrupt pin goes high and memory location 0x000 becomes 01001001. the resulting temperature in c can be read from memory locations 0 x030 to 0x033 (corresponding to ch 9 ). example: standard 4-wire rtd ( no rotation or r sense sharing) standard 4-wire rtd channel assignments follow the general convention shown in figure 13. terminal 1 is tied to ground, terminals 2 and 3 ( kelvin sensed signal) tie to ch rtd and ch rtd -1 , and the 4 th terminal ties to the sense resistor. channel assignment data ( see table 25) is mapped to memory locations corresponding to ch rtd . sense resistor channel assignments follow the general convention shown in figure 14. the sense resistor is tied between ch rsense and ch sense-1 , where ch rsense is tied to the 4 th terminal of the rtd . channel assignment data ( see table 33) is mapped into a memory location corresponding to ch rsense . figure 13. 4-wire rtd channel assignment convention figure 14. sense resistor channel assignment convention for 4-wire rtds 2983 f13 3 4 1 2 ch rtd-1 ch rtd ch rsense 4th terminal ties to sense resistor (ch rsense ) excitation current flow = ch rtd (2 rtd 20) channel assignment 2983 f14 ch rsense-1 ch rsense r sense excitation current flow = ch rsense (2 rsense 20) channel assignment ltc 2983 2983f
37 for more information www.linear.com/LTC2983 a pplica t ions i n f or m a t ion table 41. channel assignment data for 4-wire rtd (pt-1000, r sense on ch 11 , standard 4-wire, 25a excitation current, = 0.00385 standard) configuration field description # bits binary d ata memory address 0 x 230 memor y address 0 x 231 memory address 0 x 232 memory address 0 x 233 (1) rt d type pt -1000 5 01111 0 1 1 1 1 (2) sense resistor channel pointer ch 11 5 01011 0 1 0 1 1 (3) sensor configuration 4-wire, no rotate, no share 4 1000 1 0 0 0 (4) excitation current 25a 4 0011 0 0 1 1 (5) standard european, =0.00385 2 00 0 0 (6) custom rtd data pointer not custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0 table 42. channel assignment data for sense resistor (value = 5000.2) configuration field description # bits binary d ata memory address 0 x 228 memor y address 0 x 229 memory address 0 x 22a memor y address 0 x 22b (1) sensor t ype sense resistor 5 11101 1 1 1 0 1 (2) sense resistor value 5000.2 27 000010011100010000011001100 0 0 0 0 1 0 0 1 1 1 0 0 0 1 0 0 0 0 0 1 1 0 0 1 1 0 0 figure 15 shows a typical temperature measurement system using a 4-wire rtd . in this example, a 4-wire rtd s terminals tie to gnd, ch 13 , ch 12 , and ch 11 . the sense resistor ties to ch 11 and ch 10 . the sense resis- tor and rt d share a common connection at ch 11 . the rtd sensor type and configuration data are assigned to ch 13 . 32 bits of binary configuration data are mapped directly into memory locations 0 x 230 to 0x 233 (see table 41). the sense resistor is assigned to ch 11 . the user programmable value of this resistor is 5000.2. 32 bits of binary configuration data are mapped directly into memor y locations 0x228 to 0x22b (see table 42). a conversion is initiated on ch 13 by writing 10001101 into the data byte at memory location 0 x000. once the conversion is complete, the interrupt pin goes high and memory location 0 x000 becomes 01001101. the resulting temperature in c can be read from memory locations 0x040 to 0x043 (corresponding to ch 13 ). figure 15. standard 4-wire rtd example r sense 5000.2 0.1f 2983 f15 0.1f sense resistor assigned to ch 11 (ch sense=11 ) rtd assigned to ch 13 (ch rtd=13 ) ch 11 ch 10 channel assignment memory locations 0x228 to 0x22b channel assignment memory locations 0x230 to 0x233 result memory locations 0x040 to 0x043 0.1f 0.1f ch 12 ch 13 4-wire pt-1000 3 4 2 1 ltc 2983 2983f
38 for more information www.linear.com/LTC2983 a pplica t ions i n f or m a t ion example: 4-wire rtd with rotation one method to improve the accuracy of an rtd over the standard 4- wire implementation is by rotating the excita - tion current source. parasitic thermocouple effects are automatically removed through autorotation. in order to perform autorotation, the 1 st terminal of the rtd ties to ch rtd +1 instead of gnd, as in the standard case. this allows the LTC2983 to automatically change the direc- tion of the current source without the need for additional external components. 4-wire rt d with rotation channel assignments follow the general convention shown in figure 16. terminal 1 is tied to ch rtd +1 , terminals 2 and 3 ( kelvin sensed signal) tie to ch rtd and ch rtd -1 , and the 4 th terminal ties to the sense resistor. channel assignment data ( see table?25) is mapped to memory locations corresponding to ch rtd . sense resistor channel assignments follow the general convention shown in figure 17. the sense resistor is tied between ch rsense and ch rsense-1 , where ch rsense is tied to the 4 th terminal of the rtd . channel assignment data is mapped into a memory location corresponding to ch rsense . figure 16. 4-wire rtd channel assignment convention figure 17. sense resistor channel assignment convention for 4-wire rtds with rotation 2983 f17 ch rsense-1 ch rsense r sense excitation current flow = ch rsense (2 rsense 20) channel assignment 2983 f16 3 4 1 2 ch rtd?1 ch rtd ch rtd+1 excitation current flow = ch rtd (2 rtd 19) ch rsense 4 th terminal ties to sense resistor channel assignment ltc 2983 2983f
39 for more information www.linear.com/LTC2983 table 43. channel assignment data for rotating 4-wire rtd (pt -100, r sense on ch 6 , rotating 4-wire, 100a excitation current, = 0.003911 standard) configuration field description # bits binary d ata memory address 0 x 23 c memor y address 0 x 23d memor y address 0 x 23e memor y address 0 x 23f (1) rtd type pt -100 5 01100 0 1 1 0 0 (2) sense resistor channel pointer ch 6 5 00110 0 0 1 1 0 (3) sensor configuration 4-wire with rotation 4 1010 1 0 1 0 (4) excitation current 100a 4 0101 0 1 0 1 (5) standard american, =0.003911 2 01 0 1 (6) custom rtd data pointer not custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0 table 44. channel assignment data for sense resistor (value = 10.0102k) configuration field description # bits binary d ata memory address 0 x 214 memor y address 0 x 215 memory address 0 x 216 memory address 0 x 217 (1) sensor t ype sense resistor 5 11101 1 1 1 0 1 (2) sense resistor value 10.0102k 27 000100111000110100011001100 0 0 0 1 0 0 1 1 1 0 0 0 1 1 0 1 0 0 0 1 1 0 0 1 1 0 0 a pplica t ions i n f or m a t ion figure 18 shows a typical temperature measurement system using a rotating 4- wire rtd . in this example a 4- wire rtd s terminals tie to ch 17 , ch 16 , ch 15 , and ch 6 . the sense resistor is tied to ch 6 and ch 5 . the sense resistor and rtd connect together at ch 6 . the rtd sensor type and configuration data are as- signed to ch 16 . 32 bits of binary configuration data are mapped directly into memory locations 0 x23c to 0x23f (see table 43). the sense resistor is assigned to ch 6 . the u ser p rogrammable value of this resistor is 10.0102k . 32 bits of binary configuration data are mapped directly into memor y locations 0x214 to 0x217 (see table 44). a conversion is initiated on ch 16 by writing 10010000 into memory location 0 x000. once the conversion is complete, the interrupt pin goes high and memory location 0x000 becomes 01010000. the resulting temperature in c can be read from memory locations 0 x04c to 0x04f (corresponding to ch 16 ). figure 18. rotating 4-wire rtd example r sense 10.0102k 0.1f 2983 f18 0.1f sense resistor assigned to ch 6 (ch sense=6 ) rtd assigned to ch 16 (ch rtd=16 ) ch 6 ch 5 channel assignment memory locations 0x214 to 0x217 channel assignment memory locations 0x23c to 0x23f result memory locations 0x04c to 0x04f 0.1f ch 15 ch 16 ch 17 pt-100 0.1f 0.1f 3 4 2 1 ltc 2983 2983f
40 for more information www.linear.com/LTC2983 a pplica t ions i n f or m a t ion example: multiple 4-wire rtds with shared r sense figure 19 shows a typical temperature measurement system using two 4- wire rtds with a shared r sense . the LTC2983 can support up to six 4- wire rtds with a single sense resistor. in this example, the first 4-wire rtd s terminals tie to ch 17 , ch 16 , ch 15 , and ch 6 and the 2 nd ties to ch 20 , ch 19 , ch 18 , and ch 6 . the sense resistor ties to ch 5 and ch 6 . the sense resistor and both rtds connect together at ch6. this channel assignment convention is identical to that of the rotating rtd . this table 45. channel assignment data for 4-wire rtd #1 (pt -100, r sense on ch 6 , 4-wire, shared r sense , rotated 100a excitation current, = 0.003926 standard) configuration field description # bits binary d ata memory address 0 x 23 c memor y address 0 x 23d memor y address 0 x 23e memor y address 0 x 23f (1) rtd type pt -100 5 01100 0 1 1 0 0 (2) sense resistor channel pointer ch 6 5 00110 0 0 1 1 0 (3) sensor configuration 4-wire rotated 4 1010 1 0 1 0 (4) excitation current 100a 4 0101 0 1 0 1 (5) standard its-90, =0.003926 2 11 1 1 (6) custom rtd data pointer not custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0 topology supports both rotated and non-rotated rtd excitations. channel assignment data for each sensor is shown in tables 45 to 47. a conversion is initiated on ch 16 by writing 10010000 into memory location 0 x000. once the conversion is complete, the interrupt pin goes high and memory location 0x000 becomes 01010000. the resulting temperature in c can be read from memory locations 0 x04c to 0x04f (corresponding to ch 16 ). a conversion can be initiated and read from ch 19 in a similar fashion. figure 19. shared r sense 4-wire rtd example r sense 10k 0.1f 2983 f19 0.1f sense resistor assigned to ch 6 (ch sense=6 ) rtd #1 assigned to ch 16 (ch rtd=16 ) ch 6 ch 5 channel assignment memory locations 0x214 to 0x217 channel assignment memory locations 0x23c to 0x23f result memory locations 0x04c to 0x04f 0.1f ch 15 ch 16 ch 17 ch 18 ch 19 ch 20 rtd #2 assigned to ch 19 (ch rtd=19 ) channel assignment memory locations 0x248 to 0x24b result memory locations 0x058 to 0x05b 4-wire pt-100 0.1f 0.1f 3 4 2 1 0.1f 4-wire pt-500 0.1f 0.1f 3 4 2 1 ltc 2983 2983f
41 for more information www.linear.com/LTC2983 a pplica t ions i n f or m a t ion table 46. channel assignment data for 4-wire rtd #2 (pt -500, r sense on ch 6 , 4-wire, rotated 50a excitation current, = 0.003911 standard) configuration field description # bits binary d ata memory address 0 x 248 memor y address 0 x 249 memory address 0 x 24a memor y address 0 x 24b (1) rtd type pt -500 5 01110 0 1 1 1 0 (2) sense resistor channel pointer ch 6 5 00110 0 0 1 1 0 (3) sensor configuration 4-wire shared, no rotation 4 1001 1 0 0 1 (4) excitation current 50a 4 0100 0 1 0 0 (5) standard american, =0.003911 2 01 0 1 (6) custom rtd data pointer not custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0 table 47. channel assignment data for sense resistor (value = 10.000k) configuration field description # bits binary d ata memory address 0 x 214 memor y address 0 x 215 memory address 0 x 216 memory address 0 x 217 (1) sensor t ype sense resistor 5 11101 1 1 1 0 1 (2) sense resistor value 10.000k 27 000100111000100000000000000 0 0 0 1 0 0 1 1 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 example: 4-wire rtd with kelvin r sense it is possible to cancel the parasitic lead resistance in the sense resistors by configuring the 4-wire rtd with a 4-wire ( kelvin connected) sense resistor. this is useful when using a pt -10 or pt -50 with a small valued r sense or when the sense resistor is remotely located or in ap- plications requiring extreme precision. the 4- wire rtd channel assignments follow the general conventions previously defined (figures 14 and 16) for a standard 4-wire rtd . the sense resistor follows the convention shown in figure 20. figure 20. sense resistor with kelvin connections channel assignment convention 2983 f20 3 4 1 2 ch rsense?1 ch rsense?2 ch rsense r sense ties to rtd terminal 4 excitation current flow = ch rsense (3 rsense 20) channel assignment ltc 2983 2983f
42 for more information www.linear.com/LTC2983 table 48. channel assignment data for 4-wire rtd with kelvin connected r sense (pt -10, r sense on ch 6 , 4-wire, kelvin r sense with rotated 1ma excitation current, = 0.003916 standard) configuration field description # bits binary d ata memory address 0 x 23 c memor y address 0 x 23 d memor y address 0 x 23 e memor y address 0 x 23f (1) rtd type pt -10 5 01010 0 1 0 1 0 (2) sense resistor channel pointer ch 6 5 00110 0 0 1 1 0 (3) sensor configuration 4-wire kelvin r sense and rotation 4 1110 1 1 1 0 (4) excitation current 1ma 4 1000 1 0 0 0 (5) standard japanese, =0.003916 2 10 1 0 (6) custom rtd data pointer not custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0 figure 21 shows a typical temperature measurement system using a 4-wire rtd with a kelvin connected r sense . in this example, the 4-wire rtd s terminals tie to ch 17 , ch 16 , ch 15 , and ch 6 . the sense resistor ties to ch 6 , ch 5 , and ch 4 and excitation current is applied to ch 4 and ch 17 . the sense resistor s nominal value is 1 k in order to accommodate a 1 ma excitation current. the sense resistor and rtd connect together at ch 6 . this topology supports both rotated, shared and standard 4-wire rtd topologies. if rotated or shared configuration are not used then terminal 1 of the rtd is tied to ground instead of ch 17 , freeing up one input channel. channel assignment data is shown in tables 48 and 49. a conversion is initiated on ch 16 by writing 10010000 into memory location 0 x 000. once the conver - sion is complete, the interrupt pin goes high and memory location 0 x 000 becomes 01010000 ( see t able 6). the resulting temperature in c can be read from memory locations 0 x 04 c to 0 x 04f ( corresponding to ch 16 ). a pplica t ions i n f or m a t ion figure 21. sense resistor with kelvin connections example 2983 f21 sense resistor assigned to ch 6 (ch sense=6 ) ch 4 channel assignment memory locations 0x214 to 0x217 0.1f ch 5 ch 6 ch 15 ch 16 ch 17 rtd assigned to ch 16 (ch rtd=16 ) channel assignment memory locations 0x23c to 0x23f results memory locations 0x04c to 0x04f r sense 1k 0.1f 0.1f 3 4 2 1 0.1f 4-wire pt-10 0.1f 0.1f 3 4 2 1 table 49. channel assignment data for sense resistor (value = 1000) configuration field description # bits binary d ata memory address 0 x 214 memor y address 0 x 215 memory address 0 x 216 memory address 0 x 217 (1) sensor t ype sense resistor 5 11101 1 1 1 0 1 (2) sense resistor value 1000 27 000000011111010000000000000 0 0 0 0 0 0 0 1 1 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 ltc 2983 2983f
43 for more information www.linear.com/LTC2983 table 50. thermistor channel assignment word (1) thermistor type (2) sense resistor channel pointer (3) sensor configuration (4) excitation current (5) custom thermistor d ata pointer t able 51 table 27 table 52 table 53 tables 76, 77, 78, 80, 81 measurement class 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 thermistor type = 19 to 27 r sense channel pointer [4:0] sgl = 1 diff = 0 excitation mode excitation current [3:0] not used 0 0 0 custom address [5:0] custom length [5:0] table 51. thermistor type: 1/t?=?a?+?b ???ln(r)?+?c???ln(r) 2 + d???ln(r) 3 + e???ln(r) 4 + f??ln(r) 5 b31 b30 b29 b28 b27 thermistor type a b c d e f 1 0 0 1 1 thermistor 44004/44033 2.252k at 25c 1.46800e-03 2.38300e-04 0 1.00700e-07 0 0 1 0 1 0 0 thermistor 44005/44030 3k at 25c 1.40300e-03 2.37300e-04 0 9.82700e-08 0 0 1 0 1 0 1 thermistor 44007/44034 5k at 25c 1.28500e-03 2.36200e-04 0 9.28500e-08 0 0 1 0 1 1 0 thermistor 44006/44031 10k at 25c 1.03200e-03 2.38700e-04 0 1.58000e-07 0 0 1 0 1 1 1 thermistor 44008/44032 30k at 25c 9.37600e-04 2.20800e-04 0 1.27600e-07 0 0 1 1 0 0 0 thermistor ysi-400 2.252k at 25c 1.47134e-03 2.37624e-04 0 1.05034e-07 0 0 1 1 0 0 1 spectrum 1003k 1k at 25c 1.445904 e-3 2.68399e-04 0 1.64066e-07 0 0 1 1 0 1 0 thermistor custom steinhart-hart user input user input user input user input user input user input 1 1 0 1 1 thermistor custom table not used not used not used not used not used not used t hermistor m easurements channel assignment C thermistor for each thermistor tied to the LTC2983, a 32- bit channel assignment word is programmed into a memory location corresponding to the channel the sensor is tied to (see table 50). this data includes (1) thermistor type, (2) sense resistor channel pointer , (3) sensor configuration, (4) excitation current , (5) steinhart-hart address pointer or custom table address pointer. a pplica t ions i n f or m a t ion (1) thermistor type the thermistor type is determined by the first five input bits ( b 31 to b 27) as shown in table 51. linearization coef - ficients based on steinhart- hart equation for commonly used thermistor types 44004/44033, 44005/44030, 44006/44031, 44007/44034, 44008/44032 and ysi-400 are built into the device. if other custom thermistors are used, thermistor custom steinhart- hart or thermis - tor custom t able ( temperature vs resistance) can be selected. in this case, user specific data can be stored in the on- chip ram starting at the address defined in thermistor custom steinhart- hart or thermistor custom table address pointers. ltc 2983 2983f
44 for more information www.linear.com/LTC2983 table 52. sensor configuration data (3) sensor configuration sgl excit a tion mode single-ended/ differential share r sense rotate b21 b20 b19 0 0 0 differential no no 0 0 1 differential yes yes 0 1 0 differential yes no 0 1 1 reserved 1 0 0 single-ended no no 1 0 1 reserved 1 1 0 reserved 1 1 1 reserved a pplica t ions i n f or m a t ion (2) sense resistor channel pointer thermistor measurements are performed ratiometrically relative to a known r sense resistor. the sense resistor channel pointer field indicates the differential channel the sense resistor is tied to for the current thermistor (see table 27). (3) sensor configuration the sensor configuration field is used to define various thermistor properties. configuration bit b21 is set high for single-ended ( measurement relative to com) and low for differential (see table 52). the next sensor configuration bits ( b19 and b20) deter - mine the excitation current mode. these bits are used to enable r sense sharing, where one sense resistor is used for multiple thermistors. in this case, the thermistor ground connection is internal and each thermistor points to the same r sense channel. bits b19 and b 20 are also used to enable excitation current rotation to automatically remove parasitic thermocouple effects. parasitic thermocouple effects may arise from the physical connected between the thermistor and the measurement instrument. this mode is available for dif - ferential thermistor configurations using internal current source excitation. (4) excitation current the next field in the channel assignment word ( b18 to b15) controls the magnitude of the excitation current applied to the thermistor ( see table 53). in order to prevent hard or soft faults, select a current such that the maximum volt - age drop across the sensor or sense resistor is nominally 1.0v. the LTC2983 has no special requirements related to the ratio between the voltage drop across the sense resistor and the sensor. consequently, it is possible to have a sense resistor several orders of magnitude smaller than the maximum sensor value. for optimal performance over the full thermistor temperature range, auto ranged current can be selected. in this case, the LTC2983 conver - sion is performed in three cycles ( instead of the standard two cycles) ( see table 64). the first cycle determines the optimal excitation current for the sensor resistance value and r sense value. the following two cycles use that cur- rent to measure the thermistor temperature. table 53. excitation current for thermistors (4) excitation current b18 b17 b16 b15 current 0 0 0 0 reserved 0 0 0 1 250na 0 0 1 0 500na 0 0 1 1 1a 0 1 0 0 5a 0 1 0 1 10a 0 1 1 0 25a 0 1 1 1 50a 1 0 0 0 100a 1 0 0 1 250a 1 0 1 0 500a 1 0 1 1 1ma 1 1 0 0 auto range 1 1 0 1 invalid 1 1 1 0 invalid 1 1 1 1 external (5) steinhart-hart address/custom table address see custom thermistors section near the end of this data sheet for more information. ltc 2983 2983f
45 for more information www.linear.com/LTC2983 a pplica t ions i n f or m a t ion fault reporting C thermistor each sensor type has unique fault reporting mechanism in - dicated in the upper byte of the data output word. table 54 shows faults reported during the measurement of thermistors. bit d 31 indicates the thermistor or r sense is open, shorted , or not plugged in. this is a hard fault and C999 c is re- ported. bit d30 indicates a bad adc reading. this could be a result of either a broken ( open) sensor or an excessive noise event ( esd or static discharge into the sensor path). this is a hard error and C999 c is output. in the case of an excessive noise event, the device should recover and the following conversions will be valid if the noise event was a random infrequent event. bits d29 and d28 are not used for thermistors. bits d27 and d26 indicate the read - ing is over or under temperature limits ( see table 55). the calculated temperature is reported, but the accuracy may be compromised. bit d25 indicates the absolute voltage measured by the adc is beyond its normal operating range. if a thermistor is used as the cold junction element, any hard or soft error is flagged in the thermocouple result. table 54. thermistor fault reporting bit fault error type description output result d31 sensor hard fault hard open or short thermistor or r sense C999c d30 hard adc-out-of-range hard bad adc reading (could be large external noise event) C999c d29 not used for thermistors n/a always 0 valid reading d28 not used for thermistors n/a always 0 valid reading d27 sensor over range soft t > high temp limit suspect reading d26 sensor under range soft t < low temp limit suspect reading d25 adc out-of-range soft adc absolute input voltage is beyond 1.125 ? v ref /2 suspect reading d24 valid n/a result valid (should be 1) discard results if 0 valid reading ltc 2983 2983f
46 for more information www.linear.com/LTC2983 example: single-ended thermistor the simplest thermistor configuration is the single-ended configuration. thermistors using this configuration share a common ground ( com) between all sensors and are each tied to a unique sense resistor (r sense sharing is not allowed for single-ended thermistors). single-ended thermistors follow the convention shown in figure 22. terminal 1 ties to ground ( com) and terminal 2 ties to ch therm and the sense resistor. channel assignment data ( see table 50) is mapped to memory locations cor- responding to ch therm . a pplica t ions i n f or m a t ion sense resistor channel assignments follow the general convention shown in figure 23. the sense resistor is tied between ch rsense and ch rsense-1 , where ch rsense is tied to the 2 nd terminal of the thermistor. channel assignment data ( see table 33) is mapped into the memory location corresponding to ch rsense . table 55. thermistor temperature/resistance range thermistor type min () max () low temp limit (c) high temp limit (c) thermistor 44004/44033 2.252k at 25c 41.9 75.79k C40 150 thermistor 44005/44030 3k at 25c 55.6 101.0k C40 150 thermistor 44007/44034 5k at 25c 92.7 168.3k C40 150 thermistor 44006/44031 10k at 25c 237.0 239.8k C40 150 thermistor 44008/44032 30k at 25c 550.2 884.6k C40 150 thermistor ysi 400 2.252k at 25c 6.4 1.66m C80 250 spectrum 1003k 1k at 25c 51.1 39.51k C50 125 thermistor custom steinhart-hart n/a n/a n/a n/a thermistor custom table second table entry last table entry figure 22. single-ended thermistor channel assignment convention figure 23. sense resistor channel assignment convention 2983 f22 2 1 ch therm com excitation current flow = ch therm (1 therm 20) 2nd terminal ties to sense resistor (ch rsense ) channel assignment 2983 f23 ch rsense-1 ch rsense r sense excitation current flow = ch rsense (2 rsense 20) channel assignment ltc 2983 2983f
47 for more information www.linear.com/LTC2983 a pplica t ions i n f or m a t ion figure 24 shows a typical temperature measurement system using a single-ended thermistor. in this example a 10k (44031 type) thermistor is tied to a 10.1 k sense resistor. the thermistor is assigned channel ch 5 ( memory locations 0 x210 to 0 x213) and the sense resistor to ch4 (memory locations 0 x20c to 0 x20f). channel assignment data are shown in tables 56 and 57. a conversion is initiated on ch 5 by writing 10000101 into memory location 0 x000. once the conversion is complete, the interrupt pin goes high and memory location 0x000 becomes 01000101. the resulting temperature in c can be read from memory locations 0 x020 to 0x023 (corresponding to ch 5 ). table 56. channel assignment data for single-ended thermistor (44006/44031 10k at 25c type thermistor, single-ended configuration, r sense on ch 4 , 1a excitation current) configuration field description # bits binary d ata memory address 0 x 210 memor y address 0 x 211 memory address 0 x 212 memory address 0 x 213 (1) thermistor t ype 44006/44031 10k at 25c 5 10110 1 0 1 1 0 (2) sense resistor channel pointer ch 4 5 00100 0 0 1 0 0 (3) sensor configuration single-ended 3 100 1 0 0 (4) excitation current 1a 4 0011 0 0 1 1 not used set these bits to 0 3 000 0 0 0 (5) custom rtd data pointer not custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0 table 57. channel assignment data for sense resistor (value = 10.1k) configuration field description # bits binary d ata memory address 0 x 20 c memor y address 0 x 20 d memor y address 0 x 20e memor y address 0 x 20f (1) sensor t ype sense resistor 5 11101 1 1 1 0 1 (2) sense resistor value 10.1k 27 000100111011101000000000000 0 0 0 1 0 0 1 1 1 0 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 figure 24. single-ended thermistor example 2983 f24 sense resistor assigned to ch 4 (ch sense=4 ) ch 3 channel assignment memory locations 0x20c to 0x20f ch 4 ch 5 com thermistor assigned to ch 5 (ch therm=5 ) channel assignment memory locations 0x210 to 0x213 result memory locations 0x020 to 0x023 r sense 10.1k 100pf 100pf type 44031 100pf 2 1 ltc 2983 2983f
48 for more information www.linear.com/LTC2983 example: differential thermistor the differential thermistor configuration allows separate ground sensing for each sensor. in this standard differ - ential configuration, one sense resistor is used for each thermistor. differential thermistors follow the convention shown in figure 25. terminal 1 ties to ch therm and is shorted to ground and terminal 2 ties ch therm-1 to and the sense resistor. channel assignment data ( see table 50) is mapped to memory locations corresponding to ch therm . sense resistor channel assignments follow the general convention shown in figure 26. the sense resistor is tied between ch rsense and ch rsense-1 , where ch rsense is tied to the 2 nd terminal of the thermistor. channel as- signment data ( see table 33) is mapped into a memory location corresponding to ch rsense . a pplica t ions i n f or m a t ion figure 25. differential thermistor channel assignment convention figure 26. sense resistor channel assignment convention 2983 f25 2 1 ch therm ch therm?1 excitation current flow = ch therm (2 therm 20) 2nd terminal ties to sense resistor 1st terminal ties to gnd channel assignment 2983 f26 ch rsense-1 ch rsense r sense excitation current flow = ch rsense (2 rsense 20) channel assignment ltc 2983 2983f
49 for more information www.linear.com/LTC2983 table 58. channel assignment data for differential thermistor (44008/44032 30k at 25c type thermistor, differential configuration, r sense on ch 11 , auto range excitation) configuration field description # bits binary d ata memory address 0 x 230 memor y address 0 x 231 memory address 0 x 232 memory address 0 x 233 (1) thermistor t ype 44008/44032 30k at 25c 5 10111 1 0 1 1 1 (2) sense resistor channel pointer ch 11 5 01011 0 1 0 1 1 (3) sensor configuration differential, no share, no rotate 3 000 0 0 0 (4) excitation current auto range 4 1100 1 1 0 0 not used set these bits to 0 2 000 0 0 0 (5) custom rtd data pointer not custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0 table 59. channel assignment data for sense resistor (value = 9.99k) configuration field description # bits binary d ata memory address 0 x 228 memor y address 0 x 229 memory address 0 x 22a memor y address 0 x 22b (1) sensor t ype sense resistor 5 11101 1 1 1 0 1 (2) sense resistor value 9.99k 27 000100111000001100000000000 0 0 0 1 0 0 1 1 1 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 a pplica t ions i n f or m a t ion figure 27 shows a typical temperature measurement system using a differential thermistor. in this example a 30k (44032 type) thermistor is tied to a 9.99 k sense resistor. the thermistor is assigned channel ch 13 ( memory locations 0 x230 to 0 x233) and the sense resistor to ch11 (memory locations 0 x228 to 0 x22b). channel assignment data is shown in tables 58 and 59). a conversion is initiated on ch 13 by writing 10001101 into memory location 0 x000. once the conversion is complete, the interrupt pin goes high and memory location 0x000 becomes 01001101. the resulting temperature in c can be read from memory locations 0 x040 to 0x043 (corresponding to ch 13 ). figure 27. differential thermistor example 2983 f27 sense resistor assigned to ch 11 (ch sense=11 ) ch 10 channel assignment memory locations 0x228 to 0x22b ch 11 ch 12 ch 13 thermistor assigned to ch 5 (ch therm=13 ) channel assignment memory locations 0x230 to 0x233 result memory locations 0x040 to 0x043 r sense 9.99k 100pf 100pf type 44032 100pf 2 1 ltc 2983 2983f
50 for more information www.linear.com/LTC2983 a pplica t ions i n f or m a t ion example: shared/rotated differential thermistor the differential thermistor configuration allows separate internal ground sensing for each sensor. in this configura - tion, one sense resistor can be used for multiple thermis- tors. differential thermistors follow the convention shown in figure 28. terminal 1 ties to ch therm and terminal 2 ties to ch therm-1 and the sense resistor. channel assign- ment data ( see table 50) is mapped to memory locations corresponding to ch therm . sense resistor channel assignments follow the general convention shown in figure 29. the sense resistor is tied between ch rsense and ch rsense-1 , where ch sense is tied to the 2 nd terminal of the thermistor. channel assignment data ( see table 33) is mapped into a memory location corresponding to ch therm . figure 30 shows a typical temperature measurement system using a shared sense resistor and one rotated/ one non-rotated differential thermistors. in this example figure 28. thermistor with shared r sense channel assignment convention figure 29. sense resistor channel assignment convention for thermistors 2983 f28 2 1 ch therm?1 ch therm excitation current flow = ch therm (2 therm 20) 2nd terminal ties to sense resistor channel assignment 2983 f29 ch rsense-1 ch rsense r sense excitation current flow = ch rsense (2 rsense 20) channel assignment ltc 2983 2983f
51 for more information www.linear.com/LTC2983 table 60. channel assignment data differential thermistor ( 44008/44032 30k at 25 c type thermistor, differential configuration with sharing and rotation, r sense on ch 16 , 250na excitation current) configuration field description # bits binary d ata memory address 0 x 244 memor y address 0 x 245 memory address 0 x 246 memory address 0 x 247 (1) thermistor t ype 44008/44032 30k at 25c 5 10111 1 0 1 1 1 (2) sense resistor channel pointer ch 16 5 10000 1 0 0 0 0 (3) sensor configuration differential, rotate and shared 3 001 0 0 1 (4) excitation current 250na excitation current 4 0001 0 0 0 1 not used set these bits to 0 3 000 0 0 0 (5) custom rtd data pointer not custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0 a pplica t ions i n f or m a t ion a 30k (44032 type) thermistor is tied to a 10.0 k sense resistor and configured as rotated/shared. the second thermistor a 2.25k (44004 type) is configured as a non-rotated/shared. channel assignment data are shown in tables 60 to 62. a conversion is initiated on ch 18 by writing 10010010 into memory location 0 x000. once the conversion is complete, the interrupt pin goes high and memory location 0x000 becomes 01010010. the resulting temperature in c can be read from memory locations 0 x054 to 0x057 (corresponding to ch 16 ). a conversion can be initiated and read from ch20 in a similar fashion. figure 30. rotated and shared thermistor example 2983 f30 thermistor #1 assigned to ch 18 (ch therm=18 ) channel assignment memory locations 0x244 to 0x247 result memory locations 0x054 to 0x057 100pf ch 17 ch 16 ch 15 ch 18 ch 19 ch 20 thermistor #2 assigned to ch 20 (ch therm=20 ) channel assignment memory locations 0x24c to 0x24f result memory locations 0x05c to 0x05f sense resistor assigned to ch 16 (ch sense=16 ) channel assignment memory locations 0x23c to 0x23f type 44032 r sense 10k 100pf 2 1 100pf type 44033 100pf 2 1 100pf 100pf ltc 2983 2983f
52 for more information www.linear.com/LTC2983 table 62. channel assignment data for sense resistor (value = 10.0k) configuration field description # bits binary data memory address 0 x 23 c memor y address 0 x 23 d memor y address 0 x 23e memor y address 0 x 23f (1) sensor t ype sense resistor 5 11101 1 1 1 0 1 (2) sense resistor value 10.0k 27 000100111000100000000000000 0 0 0 1 0 0 1 1 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 table 61. channel assignment data differential thermistor (44004/44033 2.252k at 25c type thermistor, differential configuration with sharing and no rotation, r sense on ch 16 , 10a excitation current) configuration field description # bits binary data memory address 0 x 24 c memor y address 0 x 24 d memor y address 0 x 24e memor y address 0 x 24f (1) thermistor t ype 44004/44033 2.252k at 25c 5 10011 1 0 0 1 1 (2) sense resistor channel pointer ch 16 5 10000 1 0 0 0 0 (3) sensor configuration differential, no rotate and shared 3 010 0 1 0 (4) excitation current 10a excitation current 4 0101 0 1 0 1 not used set these bits to 0 3 000 0 0 0 (5) custom rtd data pointer not custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0 a pplica t ions i n f or m a t ion ltc 2983 2983f
53 for more information www.linear.com/LTC2983 a pplica t ions i n f or m a t ion typical application thermocouple measurements the LTC2983 includes 20 fully configurable analog input channels. each input channel can be configured to accept any sensor type. figure 31 shows a typical application digitizing multiple thermocouples. each thermocouple requires a cold junction sensor and each cold junction sensor can be shared amongst multiple thermocouples. for example, the thermocouple tied to ch1 can use the diode tied to ch2 as a cold junction sensor. however, any thermocouple ( ch1, ch3, ch5, ch6, ch9, ch10, or ch16) can use any diode ( ch2, ch4, or ch7), rtd (ch13, ch14), or thermistor ( ch19, ch20) as its cold junction compensation. the LTC2983 simultaneously measures both the thermocouple and cold junction sensor and outputs the results in c or f. figure 31. typical thermocouple application ch2 ch3 ch4 ch5 ch6 ch7 ch8 ch9 ch11 ch12 ch13 ch14 ch15 ch10 ch1 v dd q1 q2 q3 cs sdi sdo sck v refout v refp 16 48 47 46 13 14 11 43 42 41 40 39 38 37 2, 4, 6, 8, 45 2.85v to 5.25v 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 2983 f31 ch16 ch17 ch18 ch19 ch20 com 0.1f 10f 10f 1f v ref_byp 1f ldo 10f (optional, drive low to reset) spi interface 1, 3, 5, 7, 9, 12, 15, 44 reset interrupt gnd r sense r sense 4-wire rtd ltc 2983 2983f
54 for more information www.linear.com/LTC2983 a pplica t ions i n f or m a t ion typical application rtd and thermistor measurements the LTC2983 includes 20 fully configurable analog input channels. each input channel can be configured to accept any sensor type. figure 32 shows a typical application digitizing multiple rtds and thermistors. each rtd / thermistor requires a sense resistor which can be shared with multiple sensors . rtds can be configured as 2, 3, or 4- wire topologies. for example, a single sense resistor (ch1, ch2) is shared between a 4- wire rtd ( ch4, ch3), a 2-wire rtd ( ch7, ch6), two 3- wire rtds ( ch9, ch8 and ch11, ch10) and a thermistor ( ch13, ch12). this can be mixed with diode sensors ( ch15) and thermocouples (ch14). sense resistors (ch17, ch16) can also be dedi - cated to specific sensors, in this case a 4-wire rt d (ch19, ch18). current is applied through both the sense resistor and rtd /thermistor, the resulting voltages are simultane - ously measured and the results are output in c or f. figure 32. typical rtd/thermistor application ch2 ch3 ch4 ch5 ch6 ch7 ch8 ch9 ch11 ch12 ch13 ch14 ch15 ch10 ch1 q1 q2 q3 v dd r sense r sense cs sdi sdo sck v refout v refp 16 48 47 46 13 14 11 43 42 41 40 39 38 37 2, 4, 6, 8, 45 2.85v to 5.25v 17 4-wire rtd 2-wire rtd 3-wire rtd 3-wire rtd 4-wire rtd 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 2983 f32 ch16 ch17 ch18 ch19 ch20 com 0.1f 10f 10f 1f v ref_byp 1f ldo 10f (optional, drive low to reset) spi interface 1, 3, 5, 7, 9, 12, 15, 44 reset interrupt gnd ltc 2983 2983f
55 for more information www.linear.com/LTC2983 s upple m en t al i n f or m a t ion 2983 f33 ch adc single-ended channel assignment = ch adc (1 adc 20) = ch adc (2 adc 20) 24-bit ? adc 24-bit ? adc channel assignment differential com ch adc ch adc-1 ? + ? + figure 33. direct adc channel assignment conventions table 63. direct adc output format start address start address + 1 start address + 2 start address + 3 ( end address ) d 31 d 30 d 29 d 28 d 27 d 26 d 25 d 24 d 23 d 22 d 21 d 20 d 19 d 18 d 17 d 16 d 15 d 14 d 13 d 12 d 11 d 10 d9 d8 d7 d6 d5 d4 d3 d2 d1 d0 fault data sign msb lsb volts range hard range hard na na soft above soft below soft range valid always 1 2v 1 v 0.5 v 0.25 v ... integer fraction >v ref 1 1 0 0 1 0 1 clamped to factory programmed value of v ref 1.75 ? v ref /2 1 1 0 0 1 0 1 1 1 1 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.125 ? v ref /2 0 0 0 0 1 0 1 1 1 0 1 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 v ref /2 0 0 0 0 0 0 0 1 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 v ref /2 22 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Cv ref /2 22 0 0 0 0 0 0 0 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Cv ref /2 0 0 0 0 0 0 0 1 0 1 0 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 C1.125 ? v ref 0 0 0 0 0 1 1 1 0 1 0 1 0 0 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 C1.75 ? v ref 1 1 0 0 0 1 1 1 0 0 1 1 1 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 < Cv ref 1 1 0 0 0 1 1 1 clamped to factory programmed value of Cv ref direct adc measurements in addition to measuring temperature sensors, the LTC2983 can perform direct voltage measurements. any channel can be configured to perform direct single-ended or dif - ferential measurements . direct adc channel assignments follow the general convention shown in figure 33. the 32-bit channel assignment word is programmed into a memory location corresponding to the input channel. the channel assignment word is 0xf000 0000 for differ- ential readings and 0xf 400 0000 for single-ended. the positive input channel ties to ch adc for both single-ended and differential modes. for single-ended measurements the adc negative input is com while for differential mea - surements it is ch adc-1 . for single ended measurements, com can be driven with any voltage above gnd?C?50mv and below v dd? C?0.3v. the direct adc results are available in memory at a location corresponding to the conversion channel. ltc 2983 2983f
56 for more information www.linear.com/LTC2983 s upple m en t al i n f or m a t ion the data is represented as a 32- bit word ( see table 63) where the eight most significant bits are fault bits and the bottom 24 are the adc reading in volts. for direct adc readings hard fault errors do not clamp the digital output. readings beyond 1.125 ? v ref /2 exceed the normal ac- curacy range of the LTC2983 and flag a soft error; these results should be discarded. readings beyond 1.75 ? v ref /2 exceed the usable range of the LTC2983; these result in a hard fault and should be discarded. figures 34 to 36 show typical integral nonlinearity varia - tion at various supply voltages and temperatures for a differential input voltage (v ref /2) and v ref /2 common mode input voltage. figure 34. integral nonlinearity as a function of temperature at v dd = 5.25v figure 36. integral nonlinearity as a function of temperature at v dd = 2.85v figure 35. integral nonlinearity as a function of temperature at v dd = 3.3v differential input voltage (v) inl error (ppm) 2983 f34 20 15 10 5 0 ?5 ?10 ?15 ?20 ?1.5 ?0.5 0 0.5 1 1.5 ?1 90c 25c ?45c differential input voltage (v) inl error (ppm) 2983 f35 20 15 10 5 0 ?5 ?10 ?15 ?20 ?1.5 ?0.5 0 0.5 1 1.5 ?1 90c 25c ?45c differential input voltage (v) inl error (ppm) 2983 f36 20 15 10 5 0 ?5 ?10 ?15 ?20 ?1.5 ?0.5 0 0.5 1 1.5 ?1 90c 25c ?45c ltc 2983 2983f
57 for more information www.linear.com/LTC2983 s upple m en t al i n f or m a t ion table 64. 2- and 3-cycles conversion modes type of sensor configuration number of conversion cycles maximum output time thermocouple oc = 0 2 167.2ms rtd all 2 167.2ms thermistor non-autorange current 2 167.2ms diode tw o readings 2 167.2ms thermocouple oc = 1 3 251ms thermocouple oc = 0, 3-cycle cold junction 3 251ms thermistor autorange current 3 251ms diode three readings 3 251ms fault protection and anti-aliasing the LTC2983 analog input channels draw a maximum of 1 na dc. as a result, it is possible to add anti-aliasing and fault protection circuitry directly to the input of the LTC2983. the most common input circuitry is a low pass filter with 1 k to 10 k resistance ( limited by excitation current for rtds and thermistors) and a capacitor with 100pf-0.1f capacitance. this circuit can be placed directly between the thermocouples and 4- wire rtds and the LTC2983. in the case of 3- wire rtds, mismatch errors between the protection resistors can degrade the performance. thermistors requiring input projection should be tied to the LTC2983 through a kelvin type connection in order to avoid errors due to the fault protection resistors. 2- and 3-cycle conversion modes the LTC2983 performs multiple internal conversions in order to determine the sensor temperature. normally, two internal conversion cycles are required for each tempera - ture result providing a maximum output time of 167.2ms. the LTC2983 uses these two cycles to automatically remove offset/offset drift errors, reduce 1/ f noise, auto- calibrate matched internal current sources, and provide simultaneous 50/60hz noise rejection. in addition to performing two conversion cycles per result, the LTC2983 also offers several unique features by utilizing a 3 rd conversion cycle. in this case, the maximum output time is 251 ms and all the benefits of the 2- cycle modes are present (see table 64). one feature utilizing the three conversion cycle mode is the internal open circuit detect mode. typically, thermocouple open circuit detection is performed by adding a high re - sistance pull -up between the thermocouple and v cc . this method can be used with the LTC2983 while operating in the two conversion cycle mode (oc=0). this external pull-up can interact with the input protection circuitry and lead to temperature measurement errors and increased noise. these problems are eliminated by selecting the internal open circuit detection mode ( oc=1). in this case, a current is pulsed for 8 ms and allowed to settle during one conversion cycle. this is followed by the normal two conversion cycle measurement of the thermocouple. if the thermocouple is broken, the current pulse will result in an open cir cuit fault. a second feature taking advantage of the 3 rd conversion cycle is thermistor excitation current auto ranging. since a thermistors resistance varies many orders of magni - tude, the performance in the low resistance regions are compromised by the small currents required by the high resistance regions of operation. the auto ranging mode applies a test current during the first conversion cycle in order to determine the optimum current for the resistance state of the thermistor. it then uses that current to perform the thermistor measurement using the normal 2-cycle measurement. if a 3-cycle thermistor measurement is used as the cold junction sensor for a 2- cycle thermocouple measurement, the thermocouple conversion result is ready after three cycles. a third feature requiring a 3 rd conversion cycle is the three current diode measurement. in this mode, three ratioed currents are applied to the external diode in order to cancel parasitic lead resistance effects. this is useful in applications where the diode is remotely located and significant, unknown parasitic lead resistance requires cancellation. if a 3- cycle diode or thermistor measure - ment is used as the cold junction sensor for a 2-cycle thermocouple measurement, the thermocouple conversion result is ready after three cycles. ltc 2983 2983f
58 for more information www.linear.com/LTC2983 table 65. multiple conversion mask register memory location b7 b6 b5 b4 b3 b2 b1 b0 0x0f4 reserved 0x0f5 ch20 ch19 ch18 ch17 0x0f6 ch16 ch15 ch14 ch13 ch12 ch11 ch10 ch9 0x0f7 ch8 ch7 ch6 ch5 ch4 ch3 ch2 ch1 table 66. example mask register select ch20, ch19, ch16, and ch1 memory location b7 b6 b5 b4 b3 b2 b1 b0 0x0f4 reserved 0x0f5 1 1 0 0 0x0f6 1 0 0 0 0 0 0 0 0x0f7 0 0 0 0 0 0 0 1 s upple m en t al i n f or m a t ion running conversions consecutively on multiple channels generally, during the initiate conversion state, a conver - sion measurement is started on a single input chan- nel determined by the channel number ( bits b[4:0] = 00001 to 10100) written into memory location 0 x000. multiple consecutive conversions can be initiated by writing bits b[4:0]=00000 into memory location 0. conversions will be initiated on each channel selected in the mask register (see table 65). for example, using the mask data shown in table 66, after 1000000 is written into memory location 0, conversions are initiated consecutively on ch20, ch19, ch16, and ch1. once the conversions begin, the interrupt pin goes low and remains low until all conversions are complete. if the mask register is set for a channel that has no assign - ment data , that conversion step is skipped. all the results are stored in the conversion result memory locations and can be read at the conclusion of the measurement cycle. entering/exiting sleep mode the LTC2983 can be placed into sleep mode by writing 0x97 to memory location 0 x000. on the rising edge of cs following the memory write ( see figure 2) the device enters the low power sleep state. it remains in this state until cs is brought low or reset is asserted. once one of these two signals is asserted, the LTC2983 begins its start-up cycle as described in state 1: start-up section of this data sheet. mux configuration delay the LTC2983 performs 2 or 3 internal conversion cycles per temperature result. each conversion cycle is performed with different excitation and input multiplexer configura - tions. prior to each conversion, these excitation circuits and input switch configurations are changed and an internal 2ms ( typical) delay ensures settling prior to the conversion cycle in most cases. ltc 2983 2983f
59 for more information www.linear.com/LTC2983 s upple m en t al i n f or m a t ion if excessive rc time constants are present in external sensor circuits ( large bypass capacitors used for thermis- tors or rtds) it is possible to increase the settling time between current source excitation and mux switching. the extra delay is determined by the value written into the mux configuration delay register ( memory location 0x0ff). the value written into this memory location is multiplied by 100 s; therefore the maximum extra mux delay is 25.5ms (i.e. 0xff = 255 ? 100s). global configuration register the LTC2983 includes a global configuration register (memory location 0 x0f0, see figure 37). this register is used to set the notch frequency of the digital filter and temperature results format ( c or f ). the default setting is simultaneous 50/60 hz rejection (75 db rejection with 2ms mux delay). if higher 60 hz rejection is required (120db rejection), write 0 x 01 into memory location 0 x0f 0; if higher 50hz rejection is required (120 db rejection) write 0x02 into memory location 0x0f0. in addition to digitizing standard thermocouples, the LTC2983 can also digitize user-programmable, custom thermocouples ( thermocouple type=0b01001, see table 12). custom sensor data ( minimum of three, maximum of 64 pairs) reside sequentially in memory and are arranged in blocks of six bytes of monotonically increasing tabular data as mv vs temperature (see t able 67). table 67. custom thermocouple tabular data format address byte 0 byte 1 byte 2 byte 3 byte 4 byte 5 0x 250 + 6* start address table entry #1 (mv) table entry #1 (kelvin) 0x 250 + 6* start address + 6 table entry #2 (mv) table entry #2 (kelvin) 0x 250 + 6* start address + 12 table entry #3 (mv) table entry #3 (kelvin) ? ? ? ? ? ? ? ? ? max address = 0 x3 ca table entry #64 (mv) table entry #64 (kelvin) figure 37. global configuration register 2983 f37 0 = c 1 = f 00 50/60hz rejection 01 60hz rejection 10 50hz rejection 11 reserved memory location 0x0f0 0 0 0 0 0 } the default temperature units reported by the LTC2983 are c. the reported temperature can also be output in f by setting bit 3 of memory location 0 x0f0 to 1. all other global configuration bits should be set to 0. reference considerations the mechanical stress of soldering the LTC2983 to a pc board can cause the output voltage reference to shift and temperature coefficient to change. these two changes are not correlated. for example, the voltage may shift but the temperature coefficient may not. to reduce the effects of stress-related shifts, mount the reference near the short edge of the pc board or in a corner. figure 38. custom thermocouple example (mv vs kelvin) 2983 f38 temperature (k) p9 p8 p7 p6 p5 p4 p3 (0mv, 0k) note: p0 should be the extrapolation point to 0k voltage (mv) p2 p1 p0 voltage < p1 soft fault condition voltage > p9 soft fault condition (0mv, 273.15k) c us t o m ther m ocouples custom thermocouple example in this example, a simplified thermocouple curve is implemented ( see figure 38). points p1 to p9 represent the normal operating range of the custom thermocouple. voltage readings above point p9 result in a soft fault and the reported temperature is a linear extrapolation using ltc 2983 2983f
60 for more information www.linear.com/LTC2983 a slope determined by points p8 and p 9 ( the final two table entries). voltage readings below point p1 are also reported as soft faults. the temperature reported is the extrapolation between point p1 and p0, where p0 is typi - cally the sensor output voltage at 0 kelvin. if p0 is above 0 kelvin, then all sensor output voltages below p 0 ( in mv) will report 0 kelvin. c us t o m ther m ocouples in order to program the LTC2983 with the custom ther- mocouple table , both the mv data and the kelvin data are converted to 24- bit binary values ( represented as two 3- byte table entries). since most thermocouples generate negative output voltages, the mv values input to the LTC2983 are 2s compliment. the sensor output voltage (units=mv), follows the convention shown in table 69, where the first bit is the sign, the next nine are the integer part and the remaining 14 bits are the fractional part. table 68. thermocouple example mv vs kelvin (k) data memory map point sensor output voltage ( mv) temperature kelvin start address stop address by te 0 byte 1 byte 2 byte 3 byte 4 byte 5 p0 C50.22 0 0x250 0x255 p1 C30.2 99.1 0x256 0x25b p2 C5.3 135.4 0x25c 0x261 p3 0 273.15 0x262 0x267 p4 40.2 361.2 0x268 0x26d mv data temperature data p5 55.3 522.1 0x26e 0x273 (see table 69) (see table 70) p6 88.3 720.3 0x274 0x279 p7 132.2 811.2 0x27a 0x27f p8 188.7 922.5 0x280 0x285 p9 460.4 1000 0x286 0x28b table 69. example thermocouple output voltage values (mv) byte 0 byte 1 byte 2 b23 b22 b21 b20 b19 b18 b17 b16 b15 b14 b13 b12 b11 b10 b9 b8 b7 b6 b5 b4 b3 b2 b1 b0 mv sign 2 8 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 2 C1 2 C2 2 C3 2 C4 2 C5 2 C6 2 C7 2 C8 2 C9 2 C10 2 C11 2 C12 2 C13 2 C14 C50.22 1 1 1 1 0 0 1 1 0 1 1 1 0 0 0 1 1 1 1 0 1 1 0 0 C30.2 1 1 1 1 1 0 0 0 0 1 1 1 0 0 1 1 0 0 1 1 0 1 0 0 C5.3 1 1 1 1 1 1 1 0 1 0 1 0 1 1 0 0 1 1 0 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 40.2 0 0 0 0 1 0 1 0 0 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0 55.3 0 0 0 0 1 1 0 1 1 1 0 1 0 0 1 1 0 0 1 1 0 0 1 1 88.3 0 0 0 1 0 1 1 0 0 0 0 1 0 0 1 1 0 0 1 1 0 0 1 1 132.2 0 0 1 0 0 0 0 1 0 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0 188.7 0 0 1 0 1 1 1 1 0 0 1 0 1 1 0 0 1 1 0 0 1 1 0 0 460.4 0 1 1 1 0 0 1 1 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 ltc 2983 2983f
61 for more information www.linear.com/LTC2983 c us t o m ther m ocouples in order to simplify the temperature field, temperature values are input in kelvin as an unsigned value, but the final temperatures reported by the LTC2983 are reported in c or f. the sensor temperature ( kelvin), follows the convention shown in table 70, where the first 14 bits are the integer part and the remaining 10 bits are the fractional part. in this example, a custom thermocouple tied to ch1, with a cold junction sensor on ch2, is programmed with the channel assignment data shown in table 71 (refer to figure 6 for similar format). in this case the custom data begins at memory location 0x250 ( starting address is 0). the start - ing address ( offset from 0 x250) is entered in the custom thermocouple data pointer field of the channel assignment data. the table data length C1 (9 in this example) is entered into the custom thermocouple data length field of the thermocouple channel assignment word. refer to table 68 where the number of six byte entries is 10. table 70. example thermocouple temperature values byte 3 byte 4 byte 5 b23 b22 b21 b20 b19 b18 b17 b16 b15 b14 b13 b12 b11 b10 b9 b8 b7 b6 b5 b4 b3 b2 b1 b0 temperature 2 13 2 12 2 11 2 10 2 9 2 8 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 2 C1 2 C2 2 C3 2 C4 2 C5 2 C6 2 C7 2 C8 2 C9 2 C10 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 99.1 0 0 0 0 0 0 0 1 1 0 0 0 1 1 0 0 0 1 1 0 0 1 1 0 135.4 0 0 0 0 0 0 1 0 0 0 0 1 1 1 0 1 1 0 0 1 1 0 0 1 273.15 0 0 0 0 0 1 0 0 0 1 0 0 0 1 0 0 1 0 0 1 1 0 0 1 361.2 0 0 0 0 0 1 0 1 1 0 1 0 0 1 0 0 1 1 0 0 1 1 0 0 522.1 0 0 0 0 1 0 0 0 0 0 1 0 1 0 0 0 0 1 1 0 0 1 1 0 720.3 0 0 0 0 1 0 1 1 0 1 0 0 0 0 0 1 0 0 1 1 0 0 1 1 811.2 0 0 0 0 1 1 0 0 1 0 1 0 1 1 0 0 1 1 0 0 1 1 0 0 922.5 0 0 0 0 1 1 1 0 0 1 1 0 1 0 1 0 0 0 0 0 0 0 0 0 1000 0 0 0 0 1 1 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 table 71. custom thermocouple channel assignment data configuration field description # bits binary d ata memor y address 200 memory address 201 memory address 202 memory address 203 (1) thermocouple t ype type custom 5 01001 0 1 0 0 1 (2) cold junction channel pointer ch 2 5 00010 0 0 0 1 0 (3) sensor configuration single-ended, 10a open circuit 4 1100 1 1 0 0 not used set these bits to 0 6 000000 0 0 0 0 0 0 (4) custom thermocouple data pointer start address = 0 (start at 0x250) 6 000000 0 0 0 0 0 0 custom thermocouple data length-1 data length C1 = 9 (10 paired entries) 6 001010 0 0 1 0 0 1 ltc 2983 2983f
62 for more information www.linear.com/LTC2983 in addition to digitizing standard rtds, the LTC2983 can also digitize custom rtds ( rtd type=0b10010, see table?26). custom sensor data ( minimum of three, maxi - mum of 64 pairs) reside sequentially in memory and are arranged in blocks of six bytes of monotonically increasing tabular data vs temperature (see table 72). table 72. custom rtd /thermistor tabular data format address byte 0 byte 1 byte 2 byte 3 byte 4 byte 5 0x 250 + 6* start address table entry #1 () table entry #1 (kelvin) 0x 250 + 6* start address + 6 table entry #2 () table entry #2 (kelvin) 0x 250 + 6* start address + 12 table entry #3 () table entry #3 (kelvin) ? ? ? ? ? ? ? ? ? max address = 0 x3 ca table entry #64 () table entry #64 (kelvin) c us t o m r tds custom rtd example in this example, a simplified rtd curve is implemented ( see figure 39). points p1 to p9 represent the normal operating range of the custom rtd . resistance readings above point p9 result in a soft fault and the reported temperature is a linear extrapolation using a slope determined by points p8 and p 9 ( the final two table entries). resistance read - ings below point p1 are also reported as soft faults. the temperature reported is the extrapolation between point p1 and p0, where p0 is the sensor output temperature at 0 ( this point should be 0 for proper interpolation below point p1). figure 39. custom rtd example ( vs kelvin ) 2983 f39 p9 p8 p7 p6 p5 p4 p3 note: p0 should be the extrapolation point to 0 resistance () temperature (k) p2 p1 0 0 p0 resistance < p1 soft fault condition resistance > p9 soft fault condition ltc 2983 2983f
63 for more information www.linear.com/LTC2983 custom rtd table data is formatted in ( sensor output resistance) vs kelvin ( see table 73). each table entry pair spans six bytes. the first set of data can begin at any memory location greater than or equal to 0 x250 and end at or below 0x3cf. in order to program the LTC2983 with the custom rtd table, both the resistance data and the kelvin data are converted to 24- bit binary values. the sensor output c us t o m r tds resistance ( units=) follows the convention shown in table 74, where the first 13 bits are the integer part and the remaining 11 bits are the fractional part. in order to simplify the temperature field, temperature values are input in kelvin as an unsigned value, but the final temperatures reported by the LTC2983 are reported in c or f. the sensor temperature ( kelvin) follows the table 73. rtd example resistance vs kelvin data memory map point sensor output resistance () temperature (k) start address stop address by te 1 byte 2 byte 3 byte 1 byte 2 byte 3 p0 0 112.3 0x28c 0x291 p1 80 200.56 0x292 0x297 p2 150 273.16 0x298 0x29d p3 257.36 377.25 0x29e 0x2a3 p4 339.22 489.66 0x2a4 0x2a9 resistance data temperature data p5 388.26 595.22 0x2aa 0x2af p6 512.99 697.87 0x2b0 0x2b5 p7 662.3 765.14 0x2b6 0x2bb p8 743.5 801.22 0x2bc 0x2c1 p9 2001.89 900.5 0x2c2 0x2c7 table 74. example rtd resistance values byte 1 byte 2 byte 3 b23 b22 b21 b20 b19 b18 b17 b16 b15 b14 b13 b12 b11 b10 b9 b8 b7 b6 b5 b4 b3 b2 b1 b0 resistance 2 12 2 11 2 10 2 9 2 8 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 2 C1 2 C2 2 C3 2 C4 2 C5 2 C6 2 C7 2 C8 2 C9 2 C10 2 C11 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 80 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 150 0 0 0 0 0 1 0 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 257.36 0 0 0 0 1 0 0 0 0 0 0 0 1 0 1 0 1 1 1 0 0 0 0 1 339.22 0 0 0 0 1 0 1 0 1 0 0 1 1 0 0 1 1 1 0 0 0 0 1 0 388.26 0 0 0 0 1 1 0 0 0 0 1 0 0 0 1 0 0 0 0 1 0 1 0 0 512.99 0 0 0 1 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 0 1 0 1 1 662.3 0 0 0 1 0 1 0 0 1 0 1 1 0 0 1 0 0 1 1 0 0 1 1 0 743.5 0 0 0 1 0 1 1 1 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 2001.89 0 0 1 1 1 1 1 0 1 0 0 0 1 1 1 1 0 0 0 1 1 1 1 0 ltc 2983 2983f
64 for more information www.linear.com/LTC2983 convention shown in table 75, where the first 14 bits are the integer part and the remaining 10 bits are the fractional part. in this example, a custom rtd tied to ch12/13, with a sense resistor on ch10/11, is programmed with the chan - nel assignment data shown in table 76 ( refer to figure 15 for a similar format). in this case, the custom data begins at memory location 0x28c ( starting address is 10). the starting address ( offset from 0 x250) is entered in the custom rtd data pointer field of the channel assignment data. the table data length C1 (9 in this case) is entered into the custom rtd data length field of the channel as - signment word . refer to table 72 where the total number of paired entries is 10. table 75. example rtd temperature values byte 1 byte 2 byte 3 b23 b22 b21 b20 b19 b18 b17 b16 b15 b14 b13 b12 b11 b10 b9 b8 b7 b6 b5 b4 b3 b2 b1 b0 temperature 2 13 2 12 2 11 2 10 2 9 2 8 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 2 C1 2 C2 2 C3 2 C4 2 C5 2 C6 2 C7 2 C8 2 C9 2 C10 112.3 0 0 0 0 0 0 0 1 1 1 0 0 0 0 0 1 0 0 1 1 0 0 1 1 200.56 0 0 0 0 0 0 1 1 0 0 1 0 0 0 1 0 0 0 1 1 1 1 0 1 273.16 0 0 0 0 0 0 1 0 0 1 0 0 0 1 0 0 1 0 1 0 0 0 1 1 377.25 0 0 0 0 0 0 1 1 1 1 1 0 0 1 0 1 0 0 0 0 0 0 0 0 489.66 0 0 0 0 0 0 0 1 1 0 1 0 0 1 1 0 1 0 1 0 0 0 1 1 595.22 0 0 0 0 1 0 0 1 0 1 0 0 1 1 0 0 1 1 1 0 0 0 0 1 697.87 0 0 0 0 1 0 1 0 1 1 1 0 0 1 1 1 0 1 1 1 1 0 1 0 765.14 0 0 0 0 1 1 0 1 1 1 1 1 0 1 0 0 1 0 0 0 1 1 1 1 801.22 0 0 0 0 1 0 1 0 1 0 0 0 0 1 0 0 1 1 1 0 0 0 0 1 900.5 0 0 0 0 1 1 1 0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 table 76. custom rtd channel assignment data configuration field description # bits binary d ata memor y address 230 memory address 231 memory address 232 memory address 233 (1) rt d type custom 5 10010 1 0 0 1 0 (2) sense resister channel pointer ch 11 5 01011 0 1 0 1 1 (3) sensor configuration 4-wire, no rotate, no share 4 1000 1 0 0 0 (4) excitation current 25a 4 0011 0 0 1 1 (5) standard not used for custom 2 00 0 0 (6) custom rtd data pointer start address = 10 6 001010 0 0 1 0 1 0 (6) custom rtd data length-1 data length C1 = 9 10 paired entries 6 001001 0 0 1 0 0 1 c us t o m r tds ltc 2983 2983f
65 for more information www.linear.com/LTC2983 c us t o m ther m is t ors in addition to digitizing standard thermistors, the LTC2983 can also digitize custom thermistors (thermistor type=0b11011, see table 51). custom sensor data (mini - mum of three, maximum of 64 pairs) reside sequentially in memory and are arranged in blocks of six bytes of monotonically increasing tabular data vs temperature (see table 72). custom thermistor table example in this example, a simplified thermistor ntc ( negative tem - perature coefficient) curve is implemented ( see figure 40). points p 1 to p9 represent the normal operating range of the custom thermistor. resistance readings above point p9 result in a soft fault and the reported temperature is a linear extrapolation using a slope determined by points p8 and p 9 ( the final two table entries). resistance read - ings below point p1 are also reported as soft faults. the temperature reported is the extrapolation between point p1 and p0, where p0 is the sensor output temperature at 0 ( this point must be 0 for proper interpolation below point p1). in addition to ntc type thermistors, it is also possible to implement ptc ( positive temperature coefficient) type thermistors ( see figure 41). in both cases, table entries start at the minimum resistance and end at the maximum resistance value. figure 40. custom ntc thermistor example ( vs kelvin) figure 41. custom ptc thermistor example ( vs kelvin) 2983 f40 p9 p8 p7 p6 p5 p4 p3 note: p0 should be the extrapolation point to 0 resistance () temperature (k) p2 p1 0 0 p0 resistance < p1 sensor under-range soft fault condition resistance > p9 sensor over-range soft fault condition 2983 f41 p9 p8 p7 p6 p5 p4 p3 note: p0 should be the extrapolation point to 0 resistance () temperature (k) p2 p1 0 0 p0 resistance < p1 sensor under-range soft fault condition resistance > p9 sensor over-range soft fault condition ltc 2983 2983f
66 for more information www.linear.com/LTC2983 custom thermistor table data is formatted in (sensor output resistance) vs kelvin ( see table 77). each table entry pair spans six bytes. the first set of data can begin at any memory location greater than or equal to 0x250 and end below 0x3cf. in order to program the LTC2983 with the custom therm - istor table, both the resistance data and the kelvin data are converted to 24- bit binary values. the sensor output resistance ( units=) follows the convention shown in c us t o m ther m is t ors table 77. ntc thermistor example resistance vs kelvin data memory map point sensor output resistance() temperature (k) start address stop address by te 1 byte 2 byte 3 byte 1 byte 2 byte 3 p0 0 457.5 0x2c8 0x2cd p1 80 400.2 0x2ce 0x2d3 p2 184 372.3 0x2d4 0x2d9 p3 423.2 320.1 0x2da 0x2df p4 973.36 290.55 0x2e0 0x2e5 resistance data temperature data p5 2238.728 249.32 0x2e6 0x2eb p6 5149.0744 240.3 0x2ec 0x2f1 p7 26775.18688 230 0x2f2 0x2f7 p8 139230.9718 215.3 0x2f8 0x2fd p9 724001.0532 200 0x2fe 0x303 table 78, where the first 20 bits are the integer part and the remaining four bits are the fractional part. in order to simplify the temperature field, temperature values are input in kelvin as an unsigned value, but the final temperatures reported by the LTC2983 are reported in c or f. the sensor temperature ( kelvin) follows the convention shown in table 79, where the first 14 bits are the integer part and the remaining 10 bits are the fractional part. table 78. example thermistor resistance values byte 1 byte 2 byte 3 b23 b22 b21 b20 b19 b18 b17 b16 b15 b14 b13 b12 b11 b10 b9 b8 b7 b6 b5 b4 b3 b2 b1 b0 resistance 2 19 2 18 2 17 2 16 2 15 2 14 2 13 2 12 2 11 2 10 2 9 2 8 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 2 C1 2 C2 2 C3 2 C4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 80 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 184 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 1 1 0 0 0 0 0 0 0 423.2 0 0 0 0 0 0 0 0 0 0 0 1 1 0 1 0 0 1 1 1 0 0 1 1 973.36 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 1 1 0 1 0 1 0 1 2238.728 0 0 0 0 0 0 0 0 1 0 0 0 1 0 1 1 1 1 1 0 1 0 1 1 5149.074 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 1 1 1 0 1 0 0 0 1 26775.19 0 0 0 0 0 1 1 0 1 0 0 0 1 0 0 1 0 1 1 1 0 0 1 1 139231 0 0 1 0 0 0 0 1 1 1 1 1 1 1 0 1 1 1 1 1 0 0 0 0 724001.1 1 0 1 1 0 0 0 0 1 1 0 0 0 0 1 0 0 0 0 1 0 0 0 1 ltc 2983 2983f
67 for more information www.linear.com/LTC2983 table 79. example thermistor temperature values byte 1 byte 2 byte 3 b23 b22 b21 b20 b19 b18 b17 b16 b15 b14 b13 b12 b11 b10 b9 b8 b7 b6 b5 b4 b3 b2 b1 b0 temperature 2 13 2 12 2 11 2 10 2 9 2 8 2 7 2 6 2 5 2 4 2 3 2 2 2 1 2 0 2 C1 2 C2 2 C3 2 C4 2 C5 2 C6 2 C7 2 C8 2 C9 2 C10 457.5 0 0 0 0 0 1 1 1 0 0 1 0 0 1 1 0 0 0 0 0 0 0 0 0 400.2 0 0 0 0 0 1 1 0 0 1 0 0 0 0 0 0 1 1 0 0 1 1 0 0 372.3 0 0 0 0 0 1 0 1 1 1 0 1 0 0 0 1 0 0 1 1 0 0 1 1 320.1 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 1 1 0 0 1 1 0 290.55 0 0 0 0 0 1 0 0 1 0 0 0 1 0 1 0 0 0 1 1 0 0 1 1 249.32 0 0 0 0 0 0 1 1 1 1 1 0 0 1 0 1 0 1 0 0 0 1 1 1 240.3 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 1 0 0 1 1 0 0 1 1 230 0 0 0 0 0 0 1 1 1 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 215.3 0 0 0 0 0 0 1 1 0 1 0 1 1 1 0 1 0 0 1 1 0 0 1 1 200 0 0 0 0 0 0 1 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 c us t o m ther m is t ors table 80. custom thermistor channel assignment data configuration field description # bits binary d ata memor y address 210 memory address 211 memory address 212 memory address 213 (1) thermistor t ype custom table 5 11011 1 1 0 1 1 (2) sense resister channel pointer ch 4 5 00100 0 0 1 0 0 (3) sensor configuration single-ended 3 100 1 0 0 (4) excitation current 1a 4 0011 0 0 1 1 not used set these bits to 0 2 00 0 0 0 (5) custom thermistor data pointer start address = 20 6 010100 0 1 0 1 0 0 (5) custom thermistor length-1 length C1 = 9 6 001001 0 0 1 0 0 1 in this example, a custom thermistor tied to ch5, with a sense resistor on ch3/4, is programmed with the channel assignment data shown in table 80 ( refer to figure 24 for similar format). in this case the custom data begins at memory location 0x2c8 ( starting address is 20). the starting address ( offset from 0 x250) is entered in the custom thermistor data pointer field of the channel as - signment data . the table data length C1 (9 in this case) is entered into the custom thermistor data length field of the thermistor channel assignment word. ltc 2983 2983f
68 for more information www.linear.com/LTC2983 in addition to custom table driven thermistors, it is also possible to directly input steinhart-hart coefficients into the LTC2983 ( thermistor type 11010, see table? 51). steinhart- hart coefficients are commonly specified parameters provided by thermistor manufacturers. the steinhart-hart equation is: 1 t = a +b ? ln(r)+c ? ln(r) 2 +d ? ln(r) 3 +e ? ln(r) 4 +f ? ln(r) 5 c us t o m ther m is t ors steinhart-hart data is stored sequentially in any memory location greater than or equal to 0 x250 and below 0x3cf. each coefficient is represented by a standard, single- precision, ieee754 32-bit value (see table 81). example custom steinhart-hart thermistor in this example a steinhart-hart equation is entered into memory starting at location 0x300 (see table 82). table 81. steinhart-hart custom thermistor data format address coefficient value 0x250 + 4 *start address a 32-bit single-precision floating point format 0x250 + 4 *start address + 4 b 32-bit single-precision floating point format 0x250 + 4 *start address + 8 c 32-bit single-precision floating point format 0x250 + 4 *start address + 12 d 32-bit single-precision floating point format 0x250 + 4 *start address + 16 e 32-bit single-precision floating point format 0x250 + 4 *start address + 20 f 32-bit single-precision floating point format table 82. custom steinhart-hart data example coefficient value start address sign exponent mantissa msb lsb msb lsb a 1.45 e-03 0x300 0 0 1 1 1 0 1 0 1 0 1 1 1 1 1 0 0 0 0 0 1 1 0 1 1 1 1 0 1 1 0 1 b 2.68e-04 0x304 0 0 1 1 1 0 0 1 1 0 0 0 1 1 0 0 1 0 0 0 0 0 1 0 0 1 0 1 1 0 1 0 c 0 0x308 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 d 1.64e-07 0x30c 0 0 1 1 0 1 0 0 0 0 1 1 0 0 0 0 0 0 0 1 0 1 1 1 1 1 1 1 1 0 1 0 e 0 0x310 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 f 0 0x314 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ltc 2983 2983f
69 for more information www.linear.com/LTC2983 a custom thermistor tied to ch5, with a sense resistor on ch3/4, is programmed with the channel assignment data shown in table 83 ( refer to figure 24 for a similar format). in this case the custom data begins at memory location c us t o m ther m is t ors 0x 300 ( starting address is 30). the starting address (offset from 0 x250) is entered in the custom thermistor data pointer field of the channel assignment data. the data length ( set to 0) is always six 32- bit floating point words. table 83. custom steinhart-hart channel assignment data configuration field description # bits binary d ata memor y address 210 memory address 211 memory address 212 memory address 213 (1) thermistor t ype custom steinhart-hart 5 11010 1 1 0 1 0 (2) sense resister channel pointer ch 4 5 00100 0 0 1 0 0 (3) sensor configuration single-ended 3 100 1 0 0 (4) excitation current 1a 4 0011 0 0 1 1 not used set these bits to 0 2 00 0 0 0 (5) custom thermistor data pointer start address = 30 6 011110 0 1 1 1 1 0 (5) custom steinhart- hart length always set to 0 fixed at six 32-bit words 6 000000 0 0 0 0 0 0 ltc 2983 2983f
70 for more information www.linear.com/LTC2983 table 84. sensor configuration for universal hookup sensor type configuration options configuration bits see table 3-wire rtd share b18 = 1, b19 = 0 table 28 4-wire rtd share b18 = 1, b19 = 0 table 28 4-wire rtd rotate b18 = 0, b19 = 1 table 28 thermistor share b19 = 0, b20 = 1 table 52 thermistor rotate b19 = 1, b20 = 0 table 52 thermocouple single-ended b21 = 1 table 14 diode single-ended b26 = 1 table 17 c us t o m ther m is t ors universal sensor hardware the LTC2983 can be configured as a universal temperature measurement device. up to four sets of universal inputs can be applied to a single LTC2983. each of these sets can directly digitize a 3-wire rtd , 4-wire rtd , thermistor, or thermocouple without changing any on board hardware (see figure 42). each sensor can share the same four adc inputs and protection / filtering circuitry are configured using software changes ( new channel assignment data) only. one sense resistor and cold junction sensor are shared among all four banks of sensors. the LTC2983 includes many flexible, software configurable input modes. in order to share four common inputs among all four sensor types each sensor requires specific con - figuration bits ( see table 84). 3- wire rtds are configured with shared r sense , 4- wire rtds and thermistors are configured as shared and/or rotated, thermocouples are configured differential with internal ground, and diodes are configured as single-ended. ltc 2983 2983f
71 for more information www.linear.com/LTC2983 information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. p ackage descrip t ion please refer to http://www .linear.com/designtools/packaging/ for the most recent package drawings. lx48 lqfp 0113 rev a 0 ? 7 11 ? 13 0.45 ? 0.75 1.00 ref 11 ? 13 9.00 bsc a a 7.00 bsc 1 2 7.00 bsc 9.00 bsc 48 1.60 max 1.35 ? 1.45 0.05 ? 0.15 0.09 ? 0.20 0.50 bsc 0.17 ? 0.27 gauge plane 0.25 note: 1. package dimensions conform to jedec #ms-026 package outline 2. dimensions are in millimeters 3. dimensions of package do not include mold flash. mold flash shall not exceed 0.25mm on any side, if present 4. pin-1 indentifier is a molded indentation, 0.50mm diameter 5. drawing is not to scale see note: 4 c0.30 ? 0.50 r0.08 ? 0.20 7.15 ? 7.25 5.50 ref 1 2 5.50 ref 7.15 ? 7.25 48 package outline recommended solder pad layout apply solder mask to areas that are not soldered section a ? a 0.50 bsc 0.20 ? 0.30 1.30 min lx package 48-lead plastic lqfp (7mm 7mm) (reference ltc dwg # 05-08-1760 rev a) e3 ltcxxxx lx-es q_ _ _ _ _ _ xxyy tray pin 1 bevel package in tray loading orientation component pin ?a1? ltc 2983 2983f
72 for more information www.linear.com/LTC2983 ? linear technology corporation 2014 lt 1014 ? printed in usa linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax : (408) 434-0507 www.linear.com/LTC2983 r ela t e d p ar t s typical a pplica t ion part number description comments ltc2990 quad i 2 c temperature, voltage and current monitor remote and internal temperatures, 14-bit voltages and current, internal 10ppm/c reference ltc2991 octal i 2 c voltage, current, temperature monitor remote and internal temperatures, 14-bit voltages and current, internal 10ppm/c reference ltc2995 temperature sensor and voltage monitor with alert outputs monitors temperature and tw o voltages, adjustable thresholds, open drain alert outputs, temperature to voltage output with integrated 1.8v reference, 1c (max) accuracy ltc2996 temperature sensor with alert outputs monitors temperature, adjustable thresholds, open drain alert outputs, temperature to voltage output with integrated 1.8v reference, 1c (max) accuracy ltc2997 remote/internal temperature sensor temperature to voltage output with integrated 1.8v reference, 1c (max) accuracy ltc2943 20v i 2 c coulomb counter monitors charge, current, voltage and temperature with 1% accuracy. works with any battery chemistry and capacity figure 42. universal inputs allow common hardware sharing for thermocouples, diodes , thermistors, 3-wire rtds, and 4-wire rtds 2983 f42 1 4 r sense thermistor thermocouple 3-wire rtd 4-wire rtd share with all four sets of sensors 2 3 3 1 1 2 2 ch3 ch2 ch1 0.1f 10f 10f 2.85v to 5.25v LTC2983 ch4 ch5 ch6 42 36 21 20 19 18 17 48 47 46 13 14 11 43 37 2, 4, 6, 8, 45 1, 3, 5, 7, 9, 12, 15, 44 16 41 40 39 38 cs reset sdi sdo sck ch7 to ch20 22 to 35 three more sets of universal sensor inputs (optional drive low to reset) spi interface com v dd v refout v refp q1 q2 q3 1f v ref_byp 1f ldo 10f interrupt gnd ltc 2983 2983f

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