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  mma1254 rev 1, 06/2012 freescale semiconductor data sheet: technical data ? freescale semiconductor, in c., 2012. all rights reserved. low-g micromachined accelerometer the mma series of silicon capacitive, micromachined accelerometers feature signal conditioning, a 2-pole low pass filter and temperature compensation. zero-g offset full scale span and filter cut-off are factory set and require no external devices. a full system self-test capability verifies system functionality. features ? integral signal conditioning ? linear output ? 2nd order bessel filter ? calibrated self-test ? eprom parity check status ? transducer hermetically sealed at wafer level for superior reliability ? robust design, high shock survivability ? qualified aecq100, rev. f grade 2 (-40 ? c/ +105 ?c) typical applications ? vibration monitoring and recording ? appliance control ? mechanical bearing monitoring ? computer hard drive protection ? computer mouse and joysticks ? virtual reality input devices ? sports diagnostic devices and systems ordering information device name temperature range case no. package MMA1254EG ? 40?? to 105 ? c 475-01 soic-16 MMA1254EGr2 ? 40?? to 105 ? c 475-01 soic-16, tape & reel mma1254keg* ? 40?? to 105 ? c 475-01 soic-16 mma1254kegr2* ? 40?? to 105 ? c 475-01 soic-16, tape & reel *part number sourced from a different facility. mma1254 mma1254: z-axis sensitivity micromachined accelerometer 5g 16-lead soic pb-free case 475-01 figure 1. simplified accelero meter functional block diagram figure 2. pin connections g-cell sensor integrator gain filter temp comp and gain self-test control logic & eprom trim circuits clock generator oscillator v dd v out v ss st status v ss v ss v ss v out status v dd v ss st n/c n/c n/c n/c n/c n/c n/c n/c 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9
mma1254 sensors 2 freescale semiconductor electro static discharge (esd) warning: this device is se nsitive to electrostatic discharge. although the freescale accelerometers contain internal 2 kv esd protection circuitry, extra precaution must be taken by the user to protect the chip from esd. a charge of over 2000 volts can accumulate on the human body or associated test equipment. a charge of this magnitude can alter the performance or cause failure of the chip. when handling the accelerometer, proper esd precautions should be followed to avoid exposing the device to discharges which may be detrimental to its performance. table 1. maximum ratings (maximum ratings are the limits to which the device can be exposed without ca using permanent damage.) rating symbol value unit powered acceleration (all axes) g pd 1500 g unpowered acceleration (all axes) g upd 2000 g supply voltage v dd ?0.3 to +7.0 v drop test (1) 1. dropped onto concrete surface from any axis. d drop 1.2 m storage temperature range t stg ?40 to +125 c
mma1254 sensors freescale semiconductor 3 table 2. operating characteristics (unless otherwise noted: ?40c ?? t a ?? +105c, 4.75 ?? v dd ?? 5.25, acceleration = 0g, loaded output. (1) ) 1. for a loaded output the measurements are observed after an rc filter consisting of a 1 k ? resistor and a 0.1 ? f capacitor to ground. characteristic symbol min typ max unit operating range (2) supply voltage (3) supply current operating temperature range acceleration range 2. these limits define the range of operation for which the part will meet specification. 3. within the supply range of 4.75 and 5.25 volts, the device oper ates as a fully calibrated linear accelerometer. beyond these supply limits the device may operate as a linear device but is not guaranteed to be in calibration. v dd i dd t a g fs 4.75 1.1 ?40 ? 5.00 2.1 ? 5 5.25 3.0 +105 ? v ma c g output signal +1g (t a = 25c, v dd = 5.0 v) (4) +1g (v dd = 5.0 v) sensitivity (t a = 25c, v dd = 5.0 v) (5) sensitivity bandwidth response nonlinearity 4. the device can measure both + and ? acceleration. with +1g acce leration the output is at midsu pply. for positive acceleration the output will increase above v dd /2 and for negative acceleration the output will decrease below v dd /2. 5. the device is calibrated at 3g. sensit ivity limits apply to 0hz acceleration. v off v off s s f -3db nl out 2.25 2.2 380 74 42.5 ?1.0 2.5 2.5 400 80 50 ? 2.75 2.8 420 86 57.5 +1.0 v v mv/g mv/g/v hz % fso noise rms (0.1 hz ? 1.0 khz) spectral density (rms, 0.1 hz ? 1.0 khz) (6) 6. at clock frequency ? 70 khz. n rms n sd ? ? 2.0 700 4.0 ? mvrms ? g/ self-test output response (v dd = 5.0 v) input low input high input loading (7) response time (8) 7. the digital input pin has an internal pull- down current source to prevent inadvertent self test initiation due to external bo ard level leakages. 8. time for the output to reach 90% of its final value after a self-test is initiated. ? v st v il v ih i in t st 0.2 v ss 0.7? v dd ?300 ? 0.25 ? ? ?125 2.0 0.3 0.3 v dd v dd ?50 25 v/v v v ? a ms status (9), (10) output low (i load = 100 ? a) output high (i load = 100 ? a) 9. the status pin output is not valid following power-up until at least one rising edge has been applied to the self-test pin. t he status pin is high whenever the self-test input is high, as a means to check the connectivity of the se lf-test and status pins in the application. 10. the status pin output latches high if a low voltage detecti on or clock frequency failure occurs, or the eprom parity changes to odd. the status pin can be reset low if the self-test pi n is pulsed with a high input for at least 100 ? s, unless a fault conditi on continues to exist. v ol v oh ? v dd ? 0.8 ? ? 0.4 ? v v output stage performance electrical saturati on recovery time (11) full scale output range (i out = 200 ? a) capacitive load drive (12) output impedance 11. time for amplifiers to recover after an acceleration signal causes them to saturate. 12. preserves phase margin (60) to guarantee output amplifier stability. t delay v fso c l z o ? v ss + 0.25 ? ? ? ? ? 50 2.0 v dd ? 0.25 100 ? ms v pf ? mechanical characteristics transverse sensitivity (13) 13. a measure of the device's ability to reject an accele ration applied 90 from the true axis of sensitivity. v xz,yz ? ? 5.0 % fso hz
mma1254 sensors 4 freescale semiconductor principle of operation the freescale accelerometer is a surface-micromachined integrated-circuit accelerometer. the device consists of a surface micromachined capacitive sensing cell (g -cell) and a cmos signal conditioning asic contained in a single integrated circuit package. the sensing element is sealed hermetically at the wafer level using a bulk micromachined ?cap'' wafer. the g-cell is a mechanical structure formed from semiconductor materials (polysilicon) using semiconductor processes (masking and etching). it can be modeled as two stationary plates with a moveable plate in-between. the center plate can be deflected from its rest position by subjecting the system to an acceleration ( figure 3 ). when the center plate deflects, the distance from it to one fixed plate will increase by the same amount that the distance to the other plate decreases. the change in distance is a measure of acceleration. the g-cell plates form two back-to-back capacitors ( figure 4 ). as the center plate mo ves with acceleration, the distance between the plates changes and each capacitor's value will change, (c = a ? /d). where a is the area of the plate, ? is the dielectric consta nt, and d is the distance between the plates. the cmos asic uses switched capacitor techniques to measure the g-cell capacitors and extract the acceleration data from the difference between the two capacitors. the asic also signal conditions and filters (switched capacitor) the signal, providing a high level output voltage that is ratiometric and proportional to acceleration. special features filtering the freescale accelerometers contain an onboard 2-pole switched capacitor filter. a bessel implementation is used because it provides a maximally flat delay response (linear phase) thus preserving pulse shape integrity. because the filter is realized using switched capacitor techniques, there is no requirement for external passive components (resistors and capacitors) to set the cut-off frequency. self-test the sensor provides a self-t est feature that allows the verification of the mechanical and electrical integrity of the accelerometer at any time before or after installation. this feature is critical in applications such as automotive airbag systems where system integrity mu st be ensured over the life of the vehicle. a fourth ?plate'' is used in the g-cell as a self- test plate. when the user applie s a logic high input to the self- test pin, a calibrated potentia l is applied across the self-test plate and the moveable plate. the resulting electrostatic force (fe = 1 / 2 av 2 /d 2 ) causes the center plate to deflect. the resultant deflection is measured by the accelerometer's control asic and a proportional ou tput voltage results. this procedure assures that both the mechanical (g-cell) and electronic sections of the accelerometer are functioning. status freescale accelerometers include fault detection circuitry and a fault latch. the status pi n is an output from the fault latch, or'd with self-test, and is set high whenever the following event occurs: ? parity of the eprom bits becomes odd in number. the fault latch can be reset by a rising edge on the self-test input pin, unless one (or more) of the fault conditions continues to exist. acceleration figure 3. transducer physical model figure 4. equivalent circuit model
mma1254 sensors freescale semiconductor 5 basic connections pinout description figure 5. soic accelerometer with recommended connection diagram pcb layout figure 6. recommended pcb layout for interfacing accelerometer to microcontroller notes: 1. use a 0.1 ? f capacitor on v dd to decouple the power source. 2. physical coupling distance of the accelerometer to the microcontroller should be minimal. 3. place a ground plane beneath the accelerometer to reduce noise, the ground plane should be attached to all of the open ended terminals shown in figure 6 . 4. use an rc filter of 1 k ? and 0.1 ? f on the output of the accelerometer to minimize clock noise (from the switched capacitor filter circuit). 5. pcb layout of power and ground should not couple power supply noise. 6. accelerometer and microcontroller should not be a high current path. 7. a/d sampling rate and any external power supply switching frequency should be selected such that they do not interfere with the internal accelerometer sampling frequency. this will prevent aliasing errors. table 3. pin descriptions pin no. pin name description 1 thru 3 v ss redundant connections to the internal v ss and may be left unconnected. 4 v out output voltage of the accelerometer. 5 status logic output pin to indicate fault. 6 v dd the power supply input. 7 v ss the power supply ground. 8 st logic input pin used to initiate self-test. 9 thru 13 trim pins used for factory trim. leave unconnected. 14 thru 16 ? no internal connection. leave unconnected. v ss v ss v ss v out status v dd v ss st n/c n/c n/c n/c n/c n/c n/c n/c 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 8 mma1254 st v dd v ss v out output signal r1 1 k ? 4 c2 0.1 ? f 6 7 logic input v dd c1 0.1 ? f status 5 3 2 1 v ss v ss v ss r r p0 a/d in v rh v ss v dd st v out v ss v dd 0.1 ? f 1 k ? 0.1 ? f 0.1 ? f power supply 0.1 ? f p1 status microcontroller accelerometer c c c c
mma1254 sensors 6 freescale semiconductor 1. when positioned as shown, the earth's gr avity will result in a positive 1g output acceleration sensing directions 10 11 12 13 14 15 16 8 7 6 5 4 3 2 1 9 v ss v ss v ss v out status v dd v ss n/c n/c n/c n/c n/c n/c n/c n/c 16-pin soic package n/c pins are recommended to be left floating ?g +g direction of earth's gravity field (1) dynamic acceleration static acceleration -1g +1g 0g 0g v out = 2.1 v v out = 2.1 v v out = 2.5 v v out = 1.7 v st
sensors freescale semiconductor 7 mma1254 case 475-01 issue c 16 lead soic page 1 of 2 package dimensions
sensors 8 freescale semiconductor mma1254 case 475-01 issue c 16 lead soic package dimensions page 2 of 2
mma1254 sensors 9 freescale semiconductor revision history revision number revision date description of changes 0 01/2012 ? initial release 1 06/2012 ? removed keg suffix from device number, in table 2. operating char acteristics changed output signal +1g vof: vdd = 0.40, 0.50 and 0.60 to +1g (vdd =5.0 v)(4) voff vdd = 2.2, 2.5 and 2.8.
mma1254 rev. 1 06/2012 rohs-compliant and/or pb-free versions of freescale products have the functionality and electrical characteristics of their non-rohs-compliant and/or non-pb-free counterparts. for further information, see http:/www.freescale.com or contact your freescale sales representative. for information on freescale?s environmental products program, go to http://www.freescale.com/epp. how to reach us: home page: www.freescale.com web support: http://www.freescale.com/support information in this document is provided solely to enable system and software implementers to use freescale semiconduc tor products. there are no express or implied copyright licenses granted hereunder to design or fabricate any integrated circuits or integrated circuits based on the information in this document. freescale semiconductor reserves the right to make changes without further notice to any products herein. freescale semiconductor makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does freescale semiconductor assume any liability ar ising out of the application or use of any product or circuit, and specifically discl aims any and all liability, including without limitation consequential or incidental damages. ?typical? parameters that may be provided in freescale semiconductor data s heets and/or specifications can and do vary in different applications and actual performance may vary over time. all operating parameters, including ?typicals?, must be validated for each customer application by customer?s technical experts. freescale se miconductor does not convey any license under its patent rights nor the rights of others. freescale semiconductor products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the fa ilure of the freescale semiconductor product could create a situation where personal injury or death may occur. should buyer purchase or use freescale semiconductor products for any such unintended or unauthorized application, buyer shall indemni fy and hold freescale semiconductor and its officers, employees, subsidiaries, affili ates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that freescale semiconductor was negligent regarding the design or manufacture of the part. freescale? and the freescale logo are trademarks of freescale semiconductor, inc. all other product or service names are the property of their respective owners. ? freescale semiconductor, inc. 2012. all rights reserved.


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