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 which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of analog devices. a adxl105* one technology way, p.o. box 9106, norwood, ma 02062-9106, u.s.a. tel: 781/329-4700 world wide web site: http://www.analog.com fax: 781/326-8703 ? analog devices, inc., 1999 i mem s is a registered trademark of analog devices, inc. *patent pending. features monolithic ic chip 2 m g resolution 10 khz bandwidth flat amplitude response ( 6 1%) to 5 khz low bias and sensitivity drift low power 2 ma output ratiometric to supply user scalable g range on-board temperature sensor uncommitted amplifier surface mount package +2.7 v to +5.25 v single supply operation 1000 g shock survival applications automotive accurate tilt sensing with fast response machine health and vibration measurement affordable inertial sensing of velocity and position seismic sensing rotational acceleration general description the adxl105 is a high performance, high accuracy and com- plete single-axis acceleration measurement system on a single monolithic ic. the adxl105 offers significantly increased bandwidth and reduced noise versus previously available micro- machined devices. the adxl105 measures acceleration with a full-scale range up to 5 g and produces an analog voltage out- put. typical noise floor is 225 m g ? hz allowing signals below 2m g to be resolved. a 10 khz wide frequency response enables vibration measurement applications. the product exhibits sign ifi- cant reduction in offset and sensitivity drift over temperature compared to the adxl05. the adxl105 can measure both dynamic accelerations, (typi- cal of vibration) or static accelerations (such as inertial force, gravity or tilt). output scale factors from 250 mv/ g to 1.5 v/ g are set using the on-board uncommitted amplifier and external resistors. the device features an on-board temperature sensor with an output of 8 mv/ c for optional temperature compensation of offset vs. temperature for high accuracy application. the adxl105 is available in a hermetic 14-lead surface mount cerpak with versions specified for the 0 c to +70 c, and C40 c to +85 c temperature ranges. high accuracy 6 1 g to 6 5 g single axis i mem s ? accelerometer with analog input functional block diagram v dd t out st com a out v mid v in v nin uca out uncommitted amplifier adxl105 x sensor temp sensor com obsolete
rev. a C2C adxl105Cspecifications adxl105j/a parameter conditions min typ max units sensor input measurement range 1 5 7 g nonlinearity best fit straight line 0.2 % of fs alignment error 2 1 degrees cross axis sensitivity 3 z axis, @ +25 c 1 5% sensitivity 4 (ratiometric) at a out initial 225 250 275 mv/ g v s = 2.7 v 80 105 120 mv/ g vs. temperature 5, 6 0.5 % zero g bias level 5 (ratiometric) at a out zero g offset error from +2.5 v nominal C625 +625 mv vs. supply C20 +20 mv/v dd /v vs. temperature 5, 7 50 mv noise performance voltage density 7 @ +25 c 225 325 m g / ? hz noise in 100 hz bandwidth 2.25 m g rms frequency response 3 db bandwidth 10 12 khz sensor resonant frequency 13 18 khz temp sensor 4 (ratiometric) output error at +25 c from +2.5 v nominal C100 +100 mv nominal scale factor 8 mv/ c output impedance 10 k w v mid 4 (ratiometric) output error from +2.5 v nominal C15 +15 mv output impedance 10 k w self-test (proportional to v dd ) voltage delta at a out self-test 0 to 1 100 500 mv input impedance 8 30 50 k w a out output drive i = 50 m a 0.50 v s C 0.5 v capacitive load drive 1000 pf uncommitted amplifier initial offset C25 +25 mv initial offset vs. temperature 5 m v/ c common-mode range 1.0 4.0 v input bias current 9 25 na open loop gain 100 v/mv output drive i = 100 m a 0.25 v s C 0.25 v capacitive load drive 1000 pf power supply operating voltage range 2.70 5.25 v quiescent supply current at 5.0 v 1.9 2.6 ma at 2.7 v 1.3 2.0 ma turn-on time 700 m s temperature range operating range j 0 +70 c specified performance a C40 +85 c notes 1 guaranteed by tests of zero g bias, sensitivity and output swing. 2 alignment of the x axis is with respect to the long edge of the bottom half of the cerpak package. 3 cross axis sensitivity is measured with an applied acceleration in the z axis of the device. 4 this parameter is ratiometric to the supply voltage v dd . specification is shown with a 5.0 v v dd . to calculate approximate values at another v dd , multiply the specification by v dd /5 v. 5 specification refers to the maximum change in parameter from its initial value at +25 c to its worst case value at t min to t max . 6 see figure 3. 7 see figure 2. 8 cmos and ttl compatible. 9 uca input bias current is tested at final test. all min and max specifications are guaranteed. typical specifications are not tested or guaranteed. specifications subject to change without notice. (t a = t min to t max , t a = +25 8 c for j grade only, v s = +5 v, @ acceleration = 0 g , unless otherwise noted) obsolete
rev. a C3C adxl105 absolute maximum ratings* acceleration (any axis, unpowered for 0.5 ms) . . . . . .1000 g acceleration (any axis, powered for 0.5 ms) . . . . . . . . . 500 g +v s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C0.3 v to +7.0 v output short circuit duration (any pin to common) . . . . . . . . . . . . . . . . . . . . indefinite operating temperature . . . . . . . . . . . . . . . . C55 c to +125 c storage temperature . . . . . . . . . . . . . . . . . . C65 c to +150 c * stresses above those listed under absolute maximum ratings may cause perma- nent damage to the device. this is a stress rating only; the functional operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. package characteristics package u ja u jc device weight 14-lead cerpak 110 c/w 30 c/w <2 grams ordering guide model temperature range package option adxl105jqc 0 c to +70 c qc-14 adxl105aqc C40 c to +85 c qc-14 pin function descriptions pin no. name description 1t out temperature sensor output 2, 3, 5 nc no connect 4 com common 6 st self-test 7 com common (substrate) 8a out accelerometer output 9v mid v dd /2 reference voltage 10 v nin uncommitted amp noninverting input 11 v in uncommitted amp inverting input 12 uca out uncommitted amp output 13, 14 v dd power supply voltage pin configuration caution esd (electrostatic discharge) sensitive device. electrostatic charges as high as 4000 v readily accumulate on the human body and test equipment and can discharge without detection. although the adxl105 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. warning! esd sensitive device drops onto hard surfaces can cause shocks of greater than 1000 g and exceed the absolute maximum rating of the device. care should be exercised in handling to avoid damage. 14 13 12 11 10 9 8 1 2 3 4 5 6 7 14 13 12 11 10 9 8 1 2 3 4 5 6 7 14 13 12 11 10 9 8 1 2 3 4 5 6 7 a out = 2.75v a out = 2.50v a out = 2.25v figure 1. adxl105 response due to gravity top view (not to scale) 14 13 12 11 10 9 8 1 2 3 4 5 6 7 nc = no connect nc nc com nc st com v dd uca out v in v nin v mid a out t out adxl105 v dd obsolete
rev. a adxl105 C4C Ctypical performance characteristics temperature C 8c 120 C120 C50 100 0 g offset shift C mv 05 0 30 0 90 60 C30 C60 C90 figure 2. typical 0 g shift vs. temperature* temperature C 8c 5 C2 C50 100 sensitivity change C % 05 0 2 1 4 3 0 C1 figure 3. typical sensitivity shift vs. temperature* output C v 20 6 0 2.2 2.25 % of units 2.3 2.35 2.4 2.45 2.5 2.55 2.6 2.65 2.7 2.75 2.8 18 8 4 2 14 10 16 12 figure 4. 0 g output distribution* sensitivity C v/ g 25 0 0.242 0.260 0.244 % of units 0.246 0.248 0.250 0.252 0.254 0.258 10 5 20 15 0.256 figure 5. sensitivity distribution* supply voltage 2.5 0 2.7 5.5 current C ma 3.3 4 1 0.5 2 1.5 5 figure 6. typical supply current vs. supply voltage frequency C hz C6 C18 100 100000 output C db C12 10000 1000 12 C0 C6 18 figure 7. noise graph *data from several characterization lots. obsolete
rev. a C5C adxl105 supply voltage 500 26 noise C m g / hz 34 5 450 400 350 300 250 200 150 figure 8. typical noise density vs. supply voltage noise density C m g / hz 40 0 205 250 210 % of units 215 220 225 230 235 245 25 20 35 30 240 15 10 5 figure 9. noise distribution* degrees of misalignment 20 0 1.375 C0.625 % of parts C0.375 C0.0125 0.0125 0.375 0.625 1.125 14 12 18 16 0.875 10 8 6 C0.875 C1.125 C1.375 4 2 figure 10. rotational die alignment* figure 11. typical self-test response at v dd = 5 v frequency C hz 1 10000 output C db 10 100 1000 15 10 5 0 C5 C10 C15 100000 adxl105 soldered and glued to pcb adxl105 soldered to pcb figure 12. frequency response frequency C hz 1 10000 phase C degrees 10 100 1000 400 300 200 100 0 C100 C200 100000 adxl105 soldered and glued to pcb adxl105 soldered to pcb C300 figure 13. phase response *data from several characterization lots. obsolete
rev. a adxl105 C6C theory of operation the adxl105 is a complete acceleration measurement system on a single monolithic ic. it contains a polysilicon surface- micromachined sensor and bimos signal conditioning circuitry to implement an open loop acceleration measurement architec- ture. the adxl105 is capable of measuring both positive and negative accelerations to a maximum level of 5 g . the acceler- ometer also measures static acceleration such as gravity, allow- ing 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-induced forces. deflection of the structure is measured with a differential capacitor structure that consists of two independent fixed plates and a central plate attached to the moving mass. a 180 out-of-phase square wave drives the fixed plates. an acceleration causing the beam to deflect, will unbalance the differential capacitor resulting in an output square wave whose amplitude is proportional to acceleration. p hase sensi- tive demodulation techniques are then used to re ctify the signal and determine the direction of the acceleration. an uncommitted amplifier is supplied for setting the output scale factor, filtering and other analog signal processing. a ratiometric voltage output temperature sensor measures the exact die temperature and can be used for optional calibration of the accelerometer over temperature. v dd the adxl105 has two power supply (v dd ) pins, 13 and 14. the two pins should be connected directly together. the output of the adxl105 is ratiometric to the power supply. therefore a 0.22 m f decoupling capacitor between v dd and com is re- quired to reduce power supply noise. to further reduce noise, insert a resistor (and/or a ferrite bead) in series with the v dd pin. see the emc and electrical noise section for more details. com the adxl105 has two common (com) pins, 4 and 7. these two pins should be connected directly together and pin 7 grounded. st the st pin (pin 6) controls the self-test feature. when this pin is set to v dd , an electrostatic force is exerted on the beam of the accelerometer causing the beam to move. the change in output resulting from movement of the beam allows the user to test for mechanical and electrical functionality. this pin may be left open-circuit or connected to common in normal use. the self- test input is cmos and ttl compatible. a out the accelerometer output (pin 8) is set to a nominal scale fac- tor of 250 mv/ g (for v dd = 5 v). note that a out is guaranteed to source/sink a minimum of 50 m a (approximately 50 k w out- put impedance). so a buffer may be required between a out and some a-to-d converter inputs. v mid v mid is nominally v dd /2. it is primarily intended for use as a reference output for the on board uncommitted amplifier (uca) as shown in figures 14a and 14b. its output impedance is ap- proximately 10 k w . v dd t out st com a out v mid v in v nin uca out uncommitted amplifier adxl105 x sensor temp sensor output v dd r1 r2 +v com 0.22mf gain 1 2 3 4 250 500 750 1000 50kv 50kv 50kv 50kv 50kv 100kv 150kv 200kv scale C mv/ g r1 r2 a. using the uca to change the scale factor v dd t out st com a out v mid v in v nin uca out uncommitted amplifier adxl105 x sensor temp sensor output v dd r1 r2 +v com 0.22mf +v 10kv r3 r3 = 5r1 r1 > 20kv scale = (250) r2 r1 mv/ g b. using the uca to change the scale factor and zero g bias figure 14. application circuit for increasing scale factor t out the temperature sensor output is nominally 2.5 v at +25 c and typically changes 8 mv/ c, and is optimized for repeatability rather than accuracy. the output is ratiometric with supply voltage. uncommitted amplifier (uca) the uncommitted amplifier has a low noise, low drift bipolar front end design. the uca can be used to change the scale factor of the adxl105 as shown in figure 14. the uca may also be used to add a 1- or 2-pole active filter as shown in fig- ures 15a through 15d. obsolete
rev. a C7C adxl105 output scaling the acceleration output (a out ) of the adxl105 is nominally 250 mv/ g . this scale factor may not be appropriate for all appli- cations. the uca may be used to increase the scale factor. the simplest implementation would be as shown in figure 14a. since the 0 g offset of the adxl105 is 2.5 v 625 mv, using a gain of greater than 4 could result in having the uca output at 0 v or 5 v at 0 g . the solution is to add r3 and vr1, as shown in figure 14b, turning the uca into a summing amplifier. vr1 is adjusted such that the uca output is v dd /2 at 0 g . c r1 out r2 in f C3db = 1 2pcr1 gain = C r1 r2 v mid a. 1-pole low-pass filter 0.22mf out 20kv in f C3db = 30hz 20kv 0.18mf v mid b. 2-pole bessel low-pass filter r1 out r2 in f C3db = 1 2pcr2 gain = C r1 r2 c r3 r3 2.5 r1 ~ ~ v mid v mid c. 1-pole high-pass filter 44.2kv out in f C3db = 10hz 59kv 0.39m f 0.39mf v mid d. 2-pole bessel high-pass filter figure 15. uca used as active filters* device bandwidth vs. resolution in general the bandwidth selected will determine the noise floor and hence, the measurement resolution (smallest detectable acceleration) of the adxl105. since the noise of the adxl105 has the characteristic of white gaussian noise that contributes equally at all frequencies, the noise amplitude may be reduced by simply reducing the bandwidth. so the typical noise of the adxl105 is: noise ( rms ) = (225 m g /? hz ) (? bandwidth k ) where k ? 1.6 for a single-pole filter k ? 1.4 for a 2-pole filter so given a bandwidth of 1000 hz, the typical rms noise floor of an adlx105 will be: noise = (225 m g / ? hz ) ( ? 1000 1.6) = 9 m g rms for a single-pole filter and noise = (225 m g / ? hz ) ( ? 1000 1.4) = 8.4 m g rms for 2-pole filter often the peak value of the noise is desired. peak-to-peak noise can only be estimated by statistical means. table i may be used for estimating the probabilities of exceeding various peak values given the rms value. the peak-to-peak noise value will give the best estimate of the uncertainty in a single measurement. table i. estimation of peak-to-peak noise nominal peak-to- % of time that noise will peak value exceed peak-to-peak value 2 rms 32% 3 rms 13% 4 rms 4.6% 5 rms 1.2% 6 rms 0.27% 7 rms 0.047% 8 rms 0.0063% the uca may be configured to act as an active filter with gain and 0 g offset control as shown in figure 16. 0.1mf out in gain = 2 f C3db = 30hz 0.1mf 100kv 47kv 47kv 10kv v dd 47kv figure 16. uca configured as an active low-pass filter with gain and offset emc and electrical noise the design of the adxl105 is such that emi or magnetic fields do not normally affect it. since the adxl105 is ratiomet- ric, conducted electrical noise on v dd does affect the output. this is particularly true for noise at the adxl105s internal clock frequency (200 khz) and its odd harmonics. so maintain- ing a clean supply voltage is key in preserving the low noise and high resolution properties of the adxl105. one way to ensure that v dd contains no high frequency noise is to add an r-c low-pass filter near the v dd pin as shown in figure 17. using the component values shown in figure 17, noise at 200 khz is attenuated by approximately C23 db. as- suming the adxl105 consumes 2 ma, there will be a 100 mv drop across r1. this can be neglected simply by using the adxl105s v dd as the a-to-d converters reference voltage as shown in figure 17. *for other corner frequencies, consult an active filter handbook. obsolete
rev. a adxl105 C8C c3549aC1C9/99 printed in u.s.a. dynamic operation in applications where only dynamic accelerations (vibration) are of interest, it is often best to ac-couple the accelerometer output as shown in figures 15c and 15d. the advantage of ac coupling is that 0 g offset vari ability (part to part) and drifts are eliminated. low power operation the most straightforward method of lowering the adxl105s power consumption is to minimize its supply voltage. by lower- ing v dd from 5 v to 2.7 v the power consumption goes from 9.5 mw to 3.5 mw. there may be reasons why lowering the supply voltage is impractical in many applications, in which case the best way to minimize power consumption is by power cycling. the adxl105 is capable of turning on and giving an accurate reading within 700 m s (see figure 18). most microcontrollers can perform an a-to-d conversion in under 25 m s. so it is prac- tical to turn on the adxl105 and take a reading in under 750 m s. given a 100 hz sample rate the average current required at 2.7 v would be: 100 samples/s 750 m s 1.3 ma = 97.5 m a figure 18. typical turn-on response at v dd = 5 v note that if a filter is used in the uca, sufficient time must be allowed for the settling of the filter as well. broadband operation the adxl105 has a number of characteristics that permits operation over a wide frequency range. its frequency and phase response is essentially flat from dc to 10 khz (see figures 12 and 13). its sensitivity is also constant over temperature (see figure 3). in contrast, most accelerometers do not have linear response at low frequencies (in many cases, no response at very low frequencies or dc), and often have a large sensitivity tem- perature coefficient that must be compensated for. in addi- tion, the adxl105s noise floor is essentially flat from dc to 5 khz where it gently rolls off (see figure 7). the beam reso- nance at 16 khz can be seen in figure 7 where there is a small noise peak (+5 db) at the beams resonant frequency. there are no other significant noise peaks at any frequency. the resonant frequency of the beam in the adxl105 deter- mines its high frequency limit. however the resonant frequency of the cerpak package is typically around 7 khz. as a result, it is not unusual to see 6 db peaks occurring at the package reso- nant frequency (as shown in figures 12 and 13). indeed, the pcb will often have one or more resonant peaks well below 7 khz. therefore, if the application calls for accurate operation at or above 6 khz the adxl105 should be glued to the pcb in order to eliminate the amplitude response peak due to the pack- age, and careful consideration should be given to the pcb mechanical design. calibrating the adxl105 the initial value of the offset and scale factor for the adxl105 will require dc calibration for applications such as tilt measurement. for low g applications, the force of gravity is the most stable, accurate and convenient acceleration reference available. an approximate reading of the 0 g point can be determined by orienting the device parallel to the earths surface and then reading the output. for high accuracy, a calibrated fixture must be used to ensure exact 90 degree orientation to the 1 g gravity signal. an accurate sensitivity calibration method is to make a measure- ment at +1 g and C1 g . the sensitivity can be determined by the two measurements. this method has the advantage of being less sensitive to the alignment of the accelerometer because the on axis signal is proportional to the cosine of the angle. for ex- ample, a 5 error in the orientation results in only a 0.4% error in the measurement. to calibrate, the accelerometer measurement axis is pointed directly at the earth. the 1 g reading is saved and the sensor is turned 180 to measure C1 g . using the two readings and sensi- tivity is calculated: sensitivity = [1 g reading C (C1 g reading )]/2 v/g v dd t out st com a out v mid v in v nin uca out uncommitted amplifier adxl105 x sensor temp sensor v dd 0.22mf 50v com +v a-to-d converter dout vref ain com figure 17. reducing noise on v dd outline dimensions dimensions shown in inches and (mm). 14-lead cerpak (qc-14) 1 7 8 14 0.310 (7.874) 0.275 (6.985) 0.415 (10.541) max pin 1 0.300 (7.62) 0.419 (10.643) 0.394 (10.008) 0.345 (8.763) 0.290 (7.366) 0.050 (1.270) 0.016 (0.406) 88 08 0.0125 (0.318) 0.009 (0.229) seating plane 0.170 (4.318) 0.135 (3.429) 0.190 (4.826) 0.140 (3.556) 0.020 (0.508) 0.013 (0.330) 0.050 (1.27) bsc 0.020 (0.508) 0.004 (0.102) obsolete
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