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precision 2 g dual axis, pwm output accelerometer adxl212 rev. 0 information furnished by analog devices is believed to be accurate and reliable. however, no responsibility is assumed by analog devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. specifications subject to change without notice. no license is granted by implication or otherwise under any patent or patent rights of analog devices. trademarks and registered trademarks are the property of their respective owners. one technology way, p.o. box 9106, norwood, ma 02062-9106, u.s.a. tel: 781.329.4700 www.analog.com fax: 781.461.3113 ?2011 analog devices, inc. all rights reserved. features dual axis accelerometer on a single ic chip 5 mm 5 mm 2 mm lcc package 5 m g resolution at 60 hz low power: 700 a at v s = 5 v (typical) high zero g bias stability high sensitivity accuracy pulse width modulated digital outputs x- and y-axis aligned to within 0.1 (typical) bandwidth adjustment with a single capacitor single-supply operation 3500 g shock survival applications automotive tilt alarms vehicle dynamic control (vdc)/electronic stability program (esp) systems electronic chassis control electronic braking data projectors navigation platform stabilization/leveling alarms and motion detectors high accuracy, 2-axis tilt sensing general description the adxl212 is a high precision, low power, complete dual axis accelerometer with signal conditioned, duty cycle modulated outputs, all on a single monolithic ic. the adxl212 measures acceleration with a full-scale range of 2 g (typical). the adxl212 measures both dynamic acceleration (such as vibration) and static acceleration (such as gravity). the outputs are digital signals whose duty cycles (ratio of pulse width to period) are proportional to acceleration (12.5%/ g ) in each of the two sensitive axes. the duty cycle outputs can be directly measured by a microcontroller without an analog-to- digital converter (adc) or glue logic. the output period is adjustable from 0.5 ms to 10 ms via a single resistor (r set ). the typical noise floor is 500 g /hz, allowing signals below 5 m g (0.3 of inclination) to be resolved in tilt sensing applica- tions using narrow bandwidths (<60 hz). the user selects the bandwidth of the accelerometer using capacitors c x and c y at the x filt and y filt pins. bandwidths of 0.5 hz to 500 hz can be selected to suit the application. the adxl212 is available in a 5 mm 5 mm 2 mm, 8-lead hermetic lcc package. functional block diagram 09804-001 adxl212 sensor 32k ? 32k ? + v s output amp output amp dcm com st x filt y filt v s c dc c x demod c y t2 y out x out r set ac amp t2 t1 a( g ) = (t1/t2 ? 0.5)/12.5% 0 g = 50% duty cycle t2(sec) = r set /125m ? pwm output waveform sample figure 1.
adxl212 rev. 0 | page 2 of 12 table of contents features .............................................................................................. 1 applications....................................................................................... 1 general description ......................................................................... 1 functional block diagram .............................................................. 1 revision history ............................................................................... 2 specifications..................................................................................... 3 absolute maximum ratings............................................................ 4 thermal resistance ...................................................................... 4 esd caution.................................................................................. 4 pin configuration and function descriptions............................. 5 typical performance characteristics ............................................. 6 theory of operation ........................................................................ 9 performance .................................................................................. 9 applications information .............................................................. 10 power supply decoupling ......................................................... 10 setting the bandwidth using c x and c y ................................. 10 self test ........................................................................................ 10 design trade-offs for selecting filter characteristics: noise vs. bandwidth ............................................................................. 10 using the adxl212 with operating voltages other than 5 v ....................................................................................................... 11 using the adxl212 as a dual axis tilt sensor..................... 11 outline dimensions ....................................................................... 12 ordering guide .......................................................................... 12 revision history 5/11revision 0: initial version
adxl212 rev. 0 | page 3 of 12 specifications t a = C40c to +85c, v s = 5 v, c x = c y = 0.1 f, acceleration = 0 g , unless otherwise noted. all minimum and maximum specifications are guaranteed. typical specifications are not guaranteed. table 1. parameter test conditions/comments min typ max unit sensor input each axis measurement range 1 1.5 2 g nonlinearity best fit straight line 0.2 % of fs package alignment error 1 degrees alignment error x sensor to y sensor 0.01 degrees cross axis sensitivity 2 % sensitivity (ratiometric) 2 each axis sensitivity at x out , y out v s = 5 v 10 12.5 15 %/ g sensitivity change due to temperature 3 v s = 5 v 0.5 % zero g bias level (ratiometric) each axis 0 g duty cycle at x out , y out 25 50 75 % initial 0 g output deviation from ideal t a = 25c 2 % 0 g duty cycle vs. supply 1.0 4.0 %/v 0 g offset vs. temperature 2 m g /c noise performance noise density t a = 25c 500 1000 g /hz rms frequency response 4 3 db bandwidth 5 500 hz c x , c y range 5 0.002 4.7 f sensor resonant frequency 5.5 khz self test 6 duty cycle change self test (st) pin: pulled low (0) to high (1) 10 % duty cycle output stage f set 7 r set = 125 k 1 khz f set 7 tolerance r set = 125 k 0.7 1.3 khz voltage levels high i = 25 a v s ? 0.2 v low i = 25 a 200 mv t2 drift vs. temperature 35 ppm/c rise/fall time 200 ns power supply operating voltage range 3.0 5.25 v specified performance 4.75 5.25 v quiescent supply current 0.7 1.1 ma turn-on time 8 19 ms temperature range specified performance ?40 +85 c 1 guaranteed by measurement of initial offset and sensitivity. 2 sensitivity varies with v s . at v s = 3 v, sensitivity is typically 7.5%/ g . 3 defined as the output change from ambient-to-maximum temperature or ambient-to-minimum temperature. 4 actual frequency response is controlled by a user supplied external capacitor (c x , c y ). 5 bandwidth = 1/(2 32 k c). for c x , c y = 0.002 f, bandwidth = 2500 hz. for c x , c y = 4.7 f, bandwidth = 1 hz. minimum/maximum values are not tested. 6 self test response changes with v s . at v s = 3 v, self test output is typically 6%. 7 the value of f set is defined by the following equation: f set = t2 1 8 larger values of c x , c y increase turn-on time. turn-o n time is approximately 160 c x or c y + 3, where c x , c y are in f, and the resultin g turn-on time is in ms.
adxl212 rev. 0 | page 4 of 12 absolute maximum ratings table 2. parameter rating acceleration (any axis, unpowered) 1000 g acceleration (any axis, powered) 1000 g v s ?0.3 v to +7.0 v output short-circuit duration (any pin to common) indefinite operating temperature range ?55c to +125c storage temperature range ?65c to +150c stresses above those listed under absolute maximum ratings may cause permanent damage to the device. this is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. thermal resistance ja is specified for the worst-case conditions, that is, a device soldered in a circuit board for surface-mount packages. table 3. thermal resistance package type ja jc device weight 8-lead ceramic lcc 120c/w 20c/w <1.0 g esd caution t p t l t 25c to peak t s preheat critic a lzone t l to t p temper a ture time ramp-down ramp-up t smin t smax t p t l 09804-002 figure 2. recommended soldering profile table 4. soldering profile condition profile feature sn63/pb37 pb free average ramp rate (t l to t p ) 3c/sec maximum preheat minimum temperature (t smin ) 100c 150c minimum temperature (t smax ) 150c 200c time (t smin to t smax ) (t s ) 60 sec to 120 sec 60 sec to 150 sec t smax to t l ramp-up rate 3c/sec maximum time (t l ) maintained above liquidous (t l ) liquidous temperature (t l ) 183c 217c time (t l ) 60 sec to 150 sec 60 sec to 150 sec peak temperature (t p ) 240c +0c/C5c 260c +0c/C5c time within 5c of actual peak temperature (t p ) 10 sec to 30 sec 20 sec to 40 sec ramp-down rate 6c/sec maximum time 25c to peak temperature 6 minutes maximum 8 minutes maximum
adxl212 rev. 0 | page 5 of 12 pin configuration and fu nction descriptions a dxl212 top view (not to scale) st 1 t2 2 com 3 y out 4 x filt y filt x out 7 6 5 v s 8 09804-003 figure 3. pin configuration table 5. pin function descriptions pin no. mnemonic description 1 st self test. 2 t2 frequency set. connect the r set resistor to ground. t2 = r set /125 m see the theory of operation section for details. 3 com common. 4 y out y channel output. 5 x out x channel output. 6 y filt y channel filter pin. 7 x filt x channel filter pin. 8 v s voltage supply. 3 v to 5.25 v.
adxl212 rev. 0 | page 6 of 12 typical performance characteristics v s = 5 v, unless otherwise noted. percent of popul a tion (%) 0 25 20 15 10 5 09804-004 duty cycle output (%) 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 figure 4. x-axis zero g bias deviation from ideal at 25c percent of popul a tion (%) 0 30 20 25 15 10 5 09804-005 tempco (m g /c) ?1.0 ?0.9 ?0.8 ?0.7 ?0.6 ?0.5 ?0.4 ?0.3 ?0.2 ?0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 figure 5. x-axis zero g bias tempco percent of popul a tion (%) 0 30 20 25 15 10 5 09804-006 sensitivity (%/ g ) 11.70 11.85 12.00 12.15 12.30 12.45 12.60 12.75 13.90 13.05 13.20 figure 6. x-axis sensitivity at 25c percent of popul a tion (%) 0 25 20 15 10 5 09804-007 duty cycle output (%) 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 figure 7. y-axis zero g bias deviation from ideal at 25c percent of popul a tion (%) 0 40 20 25 30 35 15 10 5 09804-008 tempco (m g /c) ?1.0 ?0.9 ?0.8 ?0.7 ?0.6 ?0.5 ?0.4 ?0.3 ?0.2 ?0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 figure 8. y-axis zero g bias tempco percent of popul a tion (%) 0 30 20 25 15 10 5.0 09804-009 sensitivity (%/ g ) 11.70 11.85 12.00 12.15 12.30 12.45 12.60 12.75 13.90 13.05 13.20 figure 9. y-axis sensitivity at 25c
adxl212 rev. 0 | page 7 of 12 temperature (c) duty cycle (%) ?40 46.0 53.0 52.5 52.0 51.5 51.0 50.0 50.5 49.0 49.5 48.0 48.5 47.0 46.5 47.5 53.5 54.0 ?30 ?20 ?10 0 10 20 30 50 40 60 70 80 90 09804-010 figure 10. zero g bias vs. temperature, parts soldered to pcb percent of popul a tion (%) 0 40 25 30 35 20 15 10 5 09804-011 noise density ( g / hz) 100 110 120 130 140 160 150 190 180 170 200 210 220 240 230 250 figure 11. x-axis noise density at 25c 10.8 10.6 10.4 10.2 10.0 9.8 9.6 9.4 9.2 9.0 8.8 self test output (%) temperature (c) 09804-012 ?50 ?40 ?30 ?20 ?10 0 10 20 30 50 40 60 70 80 90 figure 12. self test response vs. temperature temperature (c) sensitivity (%/ g ) ?50 ?40 11.9 12.9 12.8 12.7 12.5 12.6 12.4 12.2 12.3 12.0 12.1 13.0 13.1 ?30 ?20 ?10 0 10 20 30 50 40 60 70 80 90 09804-013 figure 13. sensitivity vs. temperature, parts soldered to pcb percent of popul a tion (%) 0 40 25 30 35 20 15 10 5 09804-014 noise density ( g / hz) 100 110 120 130 140 160 150 190 180 170 200 210 220 240 230 250 figure 14. y-axis noise density at 25c temperature (c) current (ma) 0.3 0.8 0.7 0.6 0.5 0.4 0.9 150 100 50 0 ?50 v s = 5v v s = 3v 09804-015 figure 15. supply current vs. temperature
adxl212 rev. 0 | page 8 of 12 16 14 2 4 6 8 10 12 0 ?12.5 ?12.1 ?7.9 ?7.5 ?8.3 ?8.8 ?9.2 ?9.6 ?10.0 ?10.4 ?10.8 ?11.3 ?11.7 percent of population (%) delta in duty cycle (%) 09804-016 figure 16. x-axis self test response at 25c percent of popul a tion (%) 0 80 70 60 50 40 30 20 10 90 100 supply current (a) v s = 3v v s = 5v 200 300 400 500 600 700 800 900 1000 09804-017 figure 17. supply current at 25c 18 0 ?12.5 ?12.1 ?11.7 ?11.3 ?10.8 ?10.4 ?10.0 ?9.6 ?9.2 ?8.8 ?8.3 ?7.5 ?7.9 percent of popul a tion (%) delta in duty cycle (%) 09804-018 16 10 12 14 8 6 4 2 figure 18. y-axis self test response at 25c 09804-019 c x , c y = 0.1f time scale = 2ms/div t figure 19. turn-on time
adxl212 rev. 0 | page 9 of 12 theory of operation earth's surface 09804-020 top view (not to scale) pin 8 x out = 50% y out = 62.5% x out = 50% y out = 50% pin 8 x out = 50% y out = 37.5% pin 8 x out = 62.5% y out = 50% pin 8 x out = 37.5% y out = 50% figure 20. output resp onse vs. orientation the adxl212 is a complete dual axis acceleration measure- ment system on a single monolithic ic. it contains a polysilicon surface-micromachined sensor and signal conditioning circuitry to implement an open-loop acceleration measurement archi- tecture. the output signals are duty cycle modulated digital signals proportional to the acceleration. the adxl212 is capable of measuring both positive and negative accelerations to 2 g . the accelerometer can measure static acceleration forces such as gravity, allowing the adxl212 to be used as a tilt sensor. the sensor is a surface-micromachined polysilicon structure built on top of a silicon wafer. polysilicon springs suspend the structure over the surface of the wafer and provide a resistance against acceleration forces. deflection of the structure is measured using a differential capacitor that consists of independent fixed plates and plates attached to the moving mass. the fixed plates are driven by 180 out-of-phase square waves. acceleration deflects the beam and unbalances the differential capacitor, resulting in an output square wave with an amplitude that is proportional to acceleration. phase sensitive demodulation tech- niques are used to rectify the signal and determine the direction of the acceleration. the output of the demodulator is amplified and brought off chip through a 32 k resistor, at which point the user can set the signal bandwidth of the device by adding a capacitor. this filtering improves measurement resolution and helps prevent aliasing. after being low-pass filtered, the analog signals are converted to duty cycle modulated outputs that can be read by a counter. a single resistor (r set ) sets the period for a complete cycle (t2) according to the following equation: t2 (nominal) = r set /1 25 m a 0 g acceleration produces a 50% nominal duty cycle. the acceleration can be determined by measuring the length of the positive pulse width (t1) and the period (t2). the nominal transfer function of the adxl212 is acceleration = (( t1/t2 ) ? zero g bias)/ sensitivity where: zero g bias = 50% nominal. sensitivity = 12.5%/ g nominal. performance high performance is built into the device through innovative design techniques rather than by using additional temperature compensation circuitry. as a result, there is essentially no quantiza- tion error or nonmonotonic behavior, and temperature hysteresis is very low (typically less than 10 m g over the ?40c to +85c temperature range). figure 10 shows the zero g output performance of eight parts (x-axis and y-axis) over a C40c to +85c temperature range. figure 13 demonstrates the typical sensitivity shift over temper- ature for v s = 5 v. sensitivity stability is optimized for v s = 5 v but remains very good over the specified range; it is typically better than 2% over temperature at v s = 3 v.
adxl212 rev. 0 | page 10 of 12 applications information power supply decoupling for most applications, a single 0.1 f capacitor, c dc , adequately decouples the accelerometer from noise on the power supply. however, in some cases, particularly where noise is present at the 140 khz internal clock frequency (or any harmonic thereof), noise on the supply may cause interference on the output of the adxl212. if additional decoupling is needed, insert a 100 (or smaller) resistor or ferrite beads in the supply line of the adxl212. in addition or as an alternative to adding the resistor or ferrite beads, a larger bulk bypass capacitor (in the range of 1 f to 22 f) can be added in parallel to c dc . setting the bandwidth using c x and c y the adxl212 has provisions for band limiting the x out and y out pins. capacitors must be added at these pins to implement low-pass filtering for antialiasing and noise reduction. the equation for the 3 db bandwidth is f 3 db = 1/(2 (32 k) c ( x , y ) ) or more simply, f 3 db = 5 f/ c ( x , y ) the tolerance of the internal resistor (r filt ) can vary typically as much as 25% of its nominal value (32 k); the bandwidth varies accordingly. a minimum capacitance of 2000 pf for c x and c y is required in all cases. table 6. filter capacitor selection, c x and c y bandwidth (hz) capacitor (f) 1 4.7 10 0.47 50 0.10 100 0.05 200 0.027 500 0.01 self test the st pin controls the self test feature. when this pin is set to v s , an electrostatic force is exerted on the beam of the accelero- meter. the resulting movement of the beam allows the user to test if the accelerometer is functional. the typical change in output is 750 m g (corresponding to a duty cycle of 10%) and is additive to the accelerometer outputs. the st pin can remain open circuit, or it can be connected to ground in normal use. never expose the st pin to voltages greater than v s + 0.3 v. if the system design is such that this condition cannot be guaranteed (that is, multiple supply voltages are present), a low v f clamping diode between st and v s is recommended. design trade-offs for selecting filter characteristics: noise vs. bandwidth the chosen accelerometer bandwidth ultimately determines the measurement resolution (smallest detectable acceleration). filtering can be used to lower the noise floor, which improves the resolu- tion of the accelerometer. resolution is dependent on the analog filter capacitors at x filt and y filt . the adxl212 has a typical pwm bandwidth of 500 hz. the user must filter the signal to a bandwidth lower than 500 hz to limit aliasing errors. the adxl212 noise has the characteristics of white gaussian noise, which contributes equally at all frequencies and is described in terms of g /hz (that is, the noise is proportional to the square root of the accelerometer bandwidth). to maximize the resolu- tion and dynamic range of the accelerometer, limit bandwidth to the lowest frequency needed by the application. with the single pole roll-off characteristic, the typical noise of the adxl212 is determined by )6.1()hz/500( = bw g noiserms at 100 hz, the noise is g g noiserms m3.6)6.1100()hz/500( = = often, the peak value of the noise is desired. peak-to-peak noise can only be estimated by statistical methods. table 7 is useful for estimating the probabilities of exceeding various peak values, given the rms value. table 7. estimation of peak-to-peak noise peak-to-peak value % of time that noise exceeds nominal peak-to-peak value 2 rms 32 4 rms 4.6 6 rms 0.27 8 rms 0.006 for example, at 100 hz bandwidth, peak noise exceeds 25.2 m g 4.6% of the time. peak-to-peak noise values provide the best estimate of the uncertainty in a single measurement. table 8 lists the typical noise output of the adxl212 for various c x and c y values. table 8. filter capacitor selection (c x , c y ) bandwidth(hz) c x , c y (f) rms noise (m g ) peak-to-peak noise estimate (m g ) 10 0.47 0.64 3.8 50 0.1 1.4 8.6 100 0.047 2 12 500 0.01 4.5 27.2
adxl212 rev. 0 | page 11 of 12 using the adxl212 with operating voltages other than 5 v the adxl212 is tested and specified at v s = 5 v; however, it can be powered with v s as low as 3 v or as high as 5.25 v. some performance parameters change as the supply voltage varies. the adxl212 sensitivity varies proportionally to supply voltage. at v s = 3 v, the sensitivity is typically 7.5%/ g . the zero g bias output is ratiometric to supply voltage; therefore, the zero g output is nominally equal to 50% at all supply voltages. self test response in g is roughly proportional to the square of the supply voltage. therefore, at v s = 3 v, the self test response is equivalent to approximately 270 m g (typical), or 6%. the supply current decreases as the supply voltage decreases. typical current consumption at v dd = 3 v is 450 a. using the adxl212 as a dual axis tilt sensor a common application of the adxl212 is tilt measurement. an accelerometer uses the force of gravity as an input vector to deter- mine its orientation in space. an accelerometer is most sensitive to tilt when its sensitive axis is perpendicular to the force of gravity, that is, parallel to the surface of the earth. at this orientation, its response to changes in tilt is highest: its output changes nearly 17.5 m g per degree of tilt. when the accelerometer is oriented on axis to gravity, that is, near its +1 g or C1 g reading, the change in output acceleration per degree of tilt is negligible. at 45, its output changes by 12.2 m g per degree. dual axis tilt sensor: converting acceleration to tilt when the accelerometer is oriented with both its x-axis and y-axis parallel to the surface of the earth (reading approximately 0 g ), it can be used as a dual axis tilt sensor with a roll axis and a pitch axis. the output tilt in degrees is calculated as follows: pitch = asin ( a x /1 g ) roll = asin ( a y /1 g ) where a x and a y are accelerations in g , ranging from ?1 g to +1 g . be sure to account for overranges. it is possible for the accelerometers to output a signal greater than 1 g due to vibration, shock, or other accelerations.
adxl212 rev. 0 | page 12 of 12 outline dimensions bottom view (plating option 1, see detail a foroption2) detail a (option 2) 1 3 5 7 top view 0.075 ref r0.008 (4 plcs) 0.203 0.197 sq 0.193 0.020 0.015 0.010 (r 4 plcs ) 0.180 0.177 sq 0.174 0.087 0.078 0.069 0.008 0.006 0.004 0.077 0.070 0.063 0.054 0.050 0.046 0.030 0.025 0.020 0.028 0.020 dia 0.012 0.019 sq 0.106 0.100 0.094 r0.008 (8 plcs) 05-21-2010-d figure 21. 8-terminal cerami c leadless chip carrier [lcc] (e-8-1) dimensions shown in millimeters ordering guide model 1 number of axes specified voltage (v) temperature range package description package option adxl212aez 2 5 C40c to +85c 8-terminal ceramic leadless chip carrier [lcc] e-8-1 adxl212aezCrl 2 5 C40c to +85c 8-terminal ceramic leadless chip carrier [lcc] e-8-1 EVAL-ADXL212Z evaluation board 1 z = rohs compliant part. ?2011 analog devices, inc. all rights reserved. trademarks and registered trademarks are the property of their respective owners. d09804-0-5/11(0)

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