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precision 1.7 g single-/dual-axis i mems ? accelerometer adxl204 rev. a 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 ?2006 analog devices, inc. all rights reserved. features high performance, dual-axis accelerometer on a single ic chip specified at v s = 3.3 v 5 mm 5 mm 2 mm lcc package better than 2 m g resolution at 60 hz low power: 500 a at v s = 3.3 v (typical) high zero g bias stability high sensitivity accuracy C40c to +125c temperature range x-axis and y-axis aligned to within 0.1 (typical) bw adjustment with a single capacitor single-supply operation 3500 g shock survival rohs compliant compatible with sn/pb- and pb-free solder processes applications vehicle dynamic control (vdc)/electronic stability program (esp) systems electronic chassis controls electronic braking platform stabilization/leveling navigation alarms and motion detectors high accuracy, 2-axis tilt sensing general description the adxl204 is a high precision, low power, complete dual- axis accelerometer with signal-conditioned voltage outputs, all on a single monolithic ic. like the adxl203 , it measures acceleration with a full-scale range of 1.7 g ; however, the adxl204 is tested and specified for 3.3 v supply voltage, whereas the adxl203 is tested and specified at 5 v. both parts function well over a wide 3 v to 6 v operating voltage range. the adxl204 can measure both dynamic acceleration (for example, vibration) and static acceleration (for example, gravity). the typical noise floor is 170 g /hz, allowing signals below 2 m g (0.1 of inclination) to be resolved in tilt sensing applications using narrow bandwidths (<60 hz). the user selects the bandwidth of the accelerometer using capacitor c x and capacitor c y at the x out and y out pins. bandwidths of 0.5 hz to 2.5 khz can be selected to suit the application. the adxl204 is available in a 5 mm 5 mm 2 mm, 8-terminal hermetic lcc package. functional block diagram adxl204 sensor +5 v output amp output amp com st y out v s c dc c y r filt 32k ? demod x out c x r filt 32k ? ac amp 05512-001 figure 1.
adxl204 rev. a | 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 esd caution .................................................................................. 4 pin configuration and function descriptions ............................. 5 typical performance characteristics ............................................. 6 theory of operation ........................................................................ 9 performance .................................................................................. 9 applications ..................................................................................... 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: the noise/bw trade-off .................................................................. 10 using the adxl204 with operating voltages other than 3.3 v .......................................................................... 11 using the adxl204 as a dual-axis tilt sensor ........................ 11 outline dimensions ....................................................................... 12 ordering guide .......................................................................... 12 revision history 3/06rev. 0 to rev. a changes to format .............................................................universal changes to product title, features, and general description ... 1 changes to table 1............................................................................ 3 changes to table 2............................................................................ 4 added figure 2 and table 4............................................................. 4 changes to figure 3.......................................................................... 5 changes to figure 11 and figure 14............................................... 7 changes to table 7.......................................................................... 10 4/05revision 0: initial version
adxl204 rev. a | page 3 of 12 specifications all minimum and maximum specifications are guaranteed. typical specifications are not guaranteed. t a = C40c to +125c; v s = 3.3 v; c x = c y = 0.1 f; acceleration = 0 g , unless otherwise noted. table 1. parameter conditions min typ max unit sensor input each axis measurement range 1 1.7 g nonlinearity % of full scale 0.2 1.25 % package alignment error 1 degrees alignment error x sensor to y sensor 0.1 degrees cross axis sensitivity 1.5 3 % sensitivity (ratiometric) 2 each axis sensitivity at x out , y out v s = 3.3 v 595 620 645 mv/ g sensitivity change due to temperature 3 v s = 3.3 v 0.3 % zero g bias level (ratiometric) each axis 0 g voltage at x out , y out v s = 3.3 v 1.55 1.65 1.75 v initial 0 g output deviation from ideal v s = 3.3 v, 25c 50 m g 0 g offset vs. temperature 0.15 0.8 m g /c noise performance output noise <4 khz, v s = 3.3 v 1 3 mv rms noise density 170 g /hz rms frequency response 4 c x , c y range 5 0.002 10 f r filt tolerance 24 32 40 k sensor resonant frequency 5.5 khz self test t 6 logic input low 0.66 v logic input high 2.64 v st input resistance to ground 30 50 k output change at x out , y out self test 0 to 1 100 200 300 mv output amplifier output swing low no load 0.05 0.2 v output swing high no load 2.9 3.1 v power supply operating voltage range 3 6 v quiescent supply current 0.5 0.9 ma turn-on time 7 20 ms 1 guaranteed by measurement of initial offset and sensitivity. 2 sensitivity is essentially ratiometric to v s . for v s = 3.0 v to 3.6 v, sensit ivity is typically 185 mv/v/ g to 190 mv/v/ g . 3 defined as the change from ambient-to-maximum temperature or ambient-to-minimum temperature. 4 actual frequency response controlled by 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 = 10 f, bandwidth = 0.5 hz. minimum/maximum values are not tested. 6 self-test response changes cubically with v s . 7 larger values of c x , c y increase turn-on time. turn-o n time is approximately 160 c x or c y + 4 ms, where c x , c y are in f.
adxl204 rev. a | page 4 of 12 absolute maximum ratings table 2. parameter rating acceleration (any axis, unpowered) 3500 g acceleration (any axis, powered) 3500 g drop test (concrete surface) 1.2 m v s ?0.3 v to +7.0 v all other pins (com ? 0.3 v) to (v s + 0.3 v) output short-circuit duration (any pin to common) indefinite temperature range (powered) ?55c to +125c temperature range (storage) ?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. table 3. package characteristics package type ja jc device weight 8-terminal lcc 120c/w 20c/w <1.0 gram 05512-002 t p t l t 25c to peak t s preheat critical zone t l to t p temperature time ramp-down ramp-up t smin t smax t p t l figure 2. recommended soldering profile table 4. condition profile feature sn63/pb37 pb-free average ramp rate (t l to t p ) 3c/sec maximum 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 3c/sec time 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 6c/sec maximum time 25c to peak temperature 6 minutes maximum 8 minutes maximum esd caution esd (electrostatic discharge) sensitive device. electrosta tic charges as high as 4000 v readily accumulate on the human body and test equipment and can discharge without detection. although this product features proprietary esd protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. therefore, proper esd precautions are recommended to avoid performance degradation or loss of functionality.
adxl204 rev. a | page 5 of 12 pin configuration and fu nction descriptions a dxl204e top view (not to scale) st 1 dnc 2 com 3 dnc 4 x out y out dnc 7 6 5 v s +y +x 8 05512-022 figure 3. pin configuration table 5. pin function descriptions pin no. mnemonic description 1 st self test 2 dnc do not connect 3 com common 4 dnc do not connect 5 dnc do not connect 6 y out y channel output 7 x out x channel output 8 v s 3 v to 6 v
adxl204 rev. a | page 6 of 12 typical performance characteristics v s = 3.3 v for all graphs, unless otherwise noted. 0 35 20 25 30 15 10 5 05512-003 1.551 1.573 1.595 1.617 1.639 1.661 1.683 1.705 1.727 1.749 volts (v) percent of population (%) figure 4. x-axis zero g bias output at 25c 0 25 20 15 10 5 05512-004 ?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 m g/c percent of population (%) figure 5. x-axis zero g bias temperature coefficient 0 60 40 50 30 20 10 05512-005 0.577 0.655 0.649 0.644 0.638 0.633 0.627 0.621 0.616 0.610 0.605 0.599 0.594 0.588 0.583 v/ g percent of population (%) figure 6. x-axis sensitivity at 25c 0 35 20 25 30 15 10 5 05512-006 1.551 1.573 1.595 1.617 1.639 1.661 1.683 1.705 1.727 1.749 volts (v) percent of population (%) figure 7. y-axis zero g bias output at 25c 0 25 20 15 10 5 05512-007 ?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 m g/c percent of population (%) figure 8. y-axis zero g bias temperature coefficient 0 70 60 40 50 30 20 10 05512-008 0.577 0.655 0.649 0.644 0.638 0.633 0.627 0.621 0.616 0.610 0.605 0.599 0.594 0.588 0.583 v/ g percent of population (%) figure 9. y-axis sensitivity at 25c
adxl204 rev. a | page 7 of 12 temperature (c) voltage (1v/ g) ?50 1.590 1.710 1.698 1.686 1.674 1.662 1.650 1.638 1.626 1.614 1.602 ?40 ?30 ?20 ?10 0 10 20 30 50 40 60 70 80 90 100 110 120 130 05512-009 figure 10. zero g bias vs. temperatureparts soldered to pcb 0 45 40 34 30 25 20 15 10 5 05512-010 120 130 140 150 160 170 180 190 200 210 g / hz percent of population (%) figure 11. x-axis noise density at 25c percent sensitivity (%) percent of population (%) ?5.0 0 30 25 20 15 10 5 35 40 ?4.0 ?3.0 ?2.0 ?1.0 0 1.0 2.0 3.0 4.0 5.0 05512-011 figure 12. z vs. x cross-axis sensitivity temperature (c) sensitivity (v/ g ) ?50 0.58 0.62 0.61 0.60 0.64 0.63 0.65 ?40 ?30 ?20 ?10 0 10 20 30 50 40 60 70 80 90 100 110 120 130 05512-012 figure 13. sensitivity vs. temperatureparts soldered to pcb 0 50 45 40 34 30 25 20 15 10 5 05512-013 120 130 140 150 160 170 180 190 200 210 g / hz percent of population (%) figure 14. y-axis noise density at 25c percent sensitivity (%) percent of population (%) ?5.0 0 30 25 20 15 10 5 35 40 ?4.0 ?3.0 ?2.0 ?1.0 0 1.0 2.0 3.0 4.0 5.0 05512-014 figure 15. z vs. y cross-axis sensitivity
adxl204 rev. a | page 8 of 12 temperature (c) current (ma) 0.3 0.8 0.7 0.6 0.5 0.4 0.9 05512-015 150 100 50 0 ?50 v s = 5v v s = 3v figure 16. supply current vs. temperature 0 35 25 30 20 15 10 5 05512-016 0.135 0.269 0.256 0.242 0.229 0.216 0.202 0.189 0.175 0.162 0.148 volts (v) percent of population (%) figure 17. x-axis self-test response at 25c temperature (c) voltage (1v/ g ) ?50 0.08 0.26 0.23 0.20 0.17 0.14 0.11 0.29 0.32 ?40 ?30 ?20 ?10 0 10 20 30 50 40 60 70 80 90 100 110 120 130 05512-017 figure 18. self-test response vs. temperature percent of population (%) 0 80 70 60 50 40 30 20 10 90 100 05512-018 (a) 3v 5v 200 300 400 500 600 700 800 900 1000 figure 19. supply current at 25c 0 30 25 20 15 10 5 05512-019 0.135 0.269 0.256 0.242 0.229 0.216 0.202 0.189 0.175 0.162 0.148 volts (v) percent of population (%) figure 20. y-axis self-test response at 25c 05512-020 figure 21. turn-on timec x , c y = 0.1 f, time scale = 2 ms/div
adxl204 rev. a | page 9 of 12 theory of operation earth's surface 05512-021 top view (not to scale) pin 8 x out = 1.65v y out = 1.03v x out = 1.65v y out = 1.65v pin 8 x out = 1.65v y out = 2.27v pin 8 x out = 1.03v y out = 1.65v pin 8 x out = 2.27v y out = 1.65v figure 22. output resp onse vs. orientation the adxl204 is a complete acceleration measurement system on a single monolithic ic. the adxl204 is a dual-axis accelerometer. it contains a polysilicon surface-micromachined sensor and signal conditioning circuitry to implement an open-loop acceleration measurement architecture. the output signals are analog voltages proportional to acceleration. the adxl204 is capable of measuring both positive and negative accelerations to at least 1.7 g . the accelerometer can measure static acceleration forces, such as gravity, allowing it to be used as a tilt sensor. the sensor is a surface-micromachined polysilicon structure built on top of the 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 whose amplitude is proportional to acceleration. phase-sensitive demodulation techniques are then 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 this point, the user can set the signal bandwidth of the device by adding a capacitor. this filtering improves measurement resolution and helps prevent aliasing. performance rather than using additional temperature compensation circuitry, innovative design techniques have been used to ensure high performance is built in. as a result, there is essentially no quantization error or nonmonotonic behavior, and temperature hysteresis is very low, typically less than 10 m g over the C40c to +125c temperature range. figure 10 shows the zero g output performance of eight parts (x-axis and y-axis) over a C40c to +125c temperature range. figure 13 demonstrates the typical sensitivity shift over tem- perature for v s = 3.3 v. sensitivity stability is typically better than 1% over temperature.
adxl204 rev. a | page 10 of 12 applications 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 can cause interference on the adxl204 output. if additional decoupling is needed, a 100 , or smaller, resistor or ferrite bead can be inserted in the supply line of the adxl204. additionally, a larger bulk bypass capacitor, in the 1 f to 22 f range, can be added in parallel to c dc . setting the bandwidth using c x and c y the adxl204 has provisions for bandlimiting 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 C3 db = 1/(2(32 k) c ( x , y ) ) or more simply, f C3 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); thus, the band- width 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 325 m g (corresponding to 200 mv). this pin can be left open-circuit or connected to common in normal use. the st pin should never be exposed to voltage greater than v s + 0.3 v. if the system design is such that this condition cannot be guaranteed (that is, multiple supply voltages present), a low v f clamping diode between st and v s is recommended. design trade-offs for selecting filter characteristics: the noise/bw trade-off the accelerometer bandwidth selected ultimately determines the measurement resolution (smallest detectable acceleration). filtering can be used to lower the noise floor, which improves the resolution of the accelerometer. resolution is dependent on the analog filter bandwidth at x out and y out . the output of the adxl204 has a typical bandwidth of 2.5 khz. the user must filter the signal at this point to limit aliasing errors. the analog bandwidth must be no more than half the a/d sampling frequency to minimize aliasing. the analog bandwidth can be further decreased to reduce noise and improve resolution. the adxl204 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 accelerometers bandwidth). the user should limit bandwidth to the lowest frequency needed by the application to maximize the resolution and dynamic range of the accelerometer. with the single-pole, roll-off characteristic, the typical noise of the adxl204 is determined by rmsnoise = (170 g /hz) (bw1.6) at 100 hz the noise is rmsnoise = (170 g /hz) (bw1.6) = 2.15 m g 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 noise exceeds nominal peak-to-peak value 2 rms 32 4 rms 4.6 6 rms 0.27 8 rms 0.006
adxl204 rev. a | page 11 of 12 peak-to-peak noise values give the best estimate of the uncertainty in a single measurement and is estimated by 6 rms. table 8 gives the typical noise output of the adxl204 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 0.7 4.1 50 0.1 1.5 9.1 100 0.047 2.2 12.9 500 0.01 4.8 28.8 using the adxl204 with operating voltages other than 3.3 v the adxl204 is tested and specified at v s = 3.3 v; however, it can be powered with v s as low as 3 v or as high as 6 v. some performance parameters change as the supply voltage is varied. the adxl204 output is ratiometric, so the output sensitivity, or scale factor, varies proportionally to supply voltage. at v s = 3 v, the output sensitivity is typically 560 mv/ g . at v s = 5 v, the output sensitivity is typically 1000 mv/ g . the zero g bias output is also ratiometric, so the zero g output is nominally equal to v s /2 at all supply voltages. the output noise is not ratiometric but is absolute in volts; therefore, the noise density decreases as the supply voltage increases. this is because the scale factor (mv/ g ) increases while the noise voltage remains constant. at v s = 3 v, the noise density is typically 190 g /hz. at v s = 5 v, the noise density is typically 110 g /hz. self-test response in g is roughly proportional to the square of the supply voltage. however, when ratiometricity of sensitivity is factored in with supply voltage, self-test response in volts is roughly proportional to the cube of the supply voltage. this means at v s = 3 v, the self-test response is approximately equivalent to 150 mv, or equivalent to 270 m g (typical). at v s = 5 v, the self-test response is approximately equivalent to 750 mv, or equivalent to 750 m g (typical). the supply current decreases as the supply voltage decreases. typical current consumption at v dd = 5 v is 750 a. using the adxl204 as a dual-axis tilt sensor one of the most popular applications of the adxl204 is tilt measurement. an accelerometer uses the force of gravity as an input vector to determine the orientation of an object 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 earths surface. at this orientation, its sensitivity to changes in tilt is highest. 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. when the accelerometer is perpendicular to gravity, its output changes nearly 17.5 m g per degree of tilt. at 45, its output changes at only 12.2 m g per degree and resolution declines. dual-axis tilt sensor: converting acceleration to tilt when the accelerometer is oriented, so both its x-axis and y-axis are parallel to the earths surface, it can be used as a 2-axis tilt sensor with a roll axis and a pitch axis. once the output signal from the accelerometer is converted to an acceleration that varies between C1 g and +1 g , the output tilt in degrees is calculated as: pitch = asin ( a x /1 g ) roll = asin ( a y /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.
adxl204 rev. a | page 12 of 12 outline dimensions bottom view 1 3 5 7 0.64 1.90 2.50 2.50 0.38 diameter 0.50 diameter 1.27 1.27 1.27 4 .50 sq 5.00 sq top view r 0.38 0.20 1.78 r 0.20 figure 23. 8-terminal cerami c leadless chip carrier [lcc] (e-8) dimensions shown in millimeters ordering guide model number of axes specified voltage (v) temperature range package description package option adxl204ce 2 3.3 C40c to +125c 8-terminal ceramic leadless chip carrier (lcc) e-8 ADXL204CE-REEL 2 3.3 C40c to +125c 8-terminal ceramic leadless chip carrier (lcc) e-8 adxl204eb evaluation board ?2006 analog devices, inc. all rights reserved. trademarks and registered trademarks are the property of their respective owners. d05512-0- 3/06(a) t ttt

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