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freescale semiconductor document number: MMA8491Q data sheet: technical data rev 2.0, 11/2012 ? 2012 freescale semiconductor, inc. all rights reserved. xtrinsic MMA8491Q 3-axis multifunction digi tal accelerometer the MMA8491Q is a low voltage, 3-axis low-g accelerometer housed in a 3 mm x 3 mm qfn package. the device can accommodate two accelerometer configurations, acting as either a 45 tilt sensor or a digital output accelerometer with i 2 c bus. ? as a 45 tilt sensor, the MMA8491Q device offers extreme ease of implementation by using a single line output per axis. ? as a digital output accelerometer, the 14-bit 8g accelerometer data can be read from the device with a 1 mg/lsb sensitivity. the extreme low power capabilities of the MMA8491Q will reduce the low data rate current consumption to less than 400 na per hz. features ? extreme low power, 400 na per hz ? ultra-fast data output time, ~700 s ? 1.95v to 3.6v v dd supply range ? 3 mm x 3 mm, 0.65 mm pitch with visual solder joint inspection ? 8g full-scale range ? 14-bit digital output, 1 mg/lsb sensitivity ? output data rate (odr), implementation based from < 1 hz to 800 hz ?i 2 c digital interface ? 3-axis, 45 tilt outputs typical applications ? smart grid: tamper detect ?anti-theft ? white goods tilt ? remote controls related documentation the MMA8491Q device features and operations are described in a variety of reference manuals, user guides, and application notes. to find the most- current versions of these documents: 1. go to the freescale homepage at: http://www.freescale.com/ 2. in the keyword search box at the top of the page, enter the device number MMA8491Q. in the refine your result pane on the left, click on the documentation link. ordering information part number temperature range package shipping MMA8491Qt -40 to +85c qfn 12 tray MMA8491Qr1 -40 to +85c qfn 12 1000 pc / tape & reel pin connections MMA8491Q bottom view 12-lead industrial qfn 3 mm x 3 mm x 1.05 mm 0.65 mm pitch 1 2 3 4 10 9 8 7 xout yout zout gnd byp v dd sda en 56 12 11 scl gnd nc nc
MMA8491Q sensors 2 freescale semiconductor, inc. contents 1 block diagram and pin descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 block diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2 definition of acceleration directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.3 tilt detection outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.4 pin descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.5 recommended application diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2 mechanical and electrical specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1 absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.2 mechanical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.3 electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.4 i2c interface characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 3 modes of operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.1 active mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.2 standby mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.3 next sample acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.4 power-up timing sequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.5 45 tilt detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.6 tilt angle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 4 serial interface (i 2 c) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4.1 i2c operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4.2 single byte read . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4.3 multiple byte read . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 5 register descriptions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 5.1 register address map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 5.2 register bit map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 5.3 data registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 5.4 accelerometer output conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 6 mounting guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 6.1 overview of soldering considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 6.2 halogen content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 6.3 pcb mounting recommendations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 7 tape and reel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 7.1 tape dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 7.2 label and device orientation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 8 package dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 9 revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
MMA8491Q sensors freescale semiconductor, inc. 3 1 block diagram and pin descriptions 1.1 block diagram figure 1. MMA8491Q block diagram 1.2 definition of a cceleration directions figure 2. acceleration direction definitions xout yout embedded functions c-to-v internal osc clock gen converter gnd x-axis transducer y-axis transducer z-axis transducer v dd zout en adc i 2 c sda scl byp voltage regulator x y z pin 1 (top view)
MMA8491Q sensors 4 freescale semiconductor, inc. 1.3 tilt detection outputs the MMA8491Q has 3 tilt detection outputs: xout, yout, zout. figure 3 shows the output results at the 6 different orientation positions. figure 3. x, y, z output based on MMA8491Q orientation pu = portrait up lr = landscape right pd = portrait down ll = landscape left 263 8491 alyw top view earth gravity pin 1 xout = 0 @ 0g yout = 1 @ -1g zout = 0 @ 0g xout = 1 @ 1g yout = 0 @ 0g zout = 0 @ 0g xout = 0 @ 0g yout = 1 @ 1g zout = 0 @ 0g xout = 1 @ -1g yout = 0 @ 0g zout = 0 @ 0g side view front xout = 0 @ 0g yout = 0 @ 0g zout = 1 @ 1g back xout = 0 @ 0g yout = 0 @ 0g zout = 1 @ -1g 263 8491 alyw 263 8491 alyw 263 8491 alyw pu ll pd lr
MMA8491Q sensors freescale semiconductor, inc. 5 1.4 pin descriptions MMA8491Q is hosted in a 12-pin 3 mm x 3 mm qfn package. ten pins are used for functions; two pins are unconnected. refer to tab l e 1 for complete pin descriptions and functions. figure 4. pin connections (top view) table 1. pin descriptions pin # pin name function description pin status 1byp internal regulator output capacitor connection the internal regulator voltage of 1.8v is present on this pin. connect to external 0.1 f bypass capacitor. output 2v dd power supply device power is supplied through the v dd line. power supply decoupling capacitors should be placed as near as possible to pin 1 of the device. input 3sda i 2 c data i 2 c slave data line ?7-bit i 2 c device addres s is 0x55. ? the sda and scl i2c connections are open drain, and therefore usually require a pullup resistor input/output 4en enable pin the enable pin fully turns on the accelerometer system when it is pulled up to logic high. the accelerometer system is turned off when the enable pin is logic low. input 5scl i 2 c clock i 2 c slave clock line input 6gnd ground ground 7gnd ground ground 8 zout push-pull z-axis tilt detection output ? output is high when acceleration is > 0.688g (axis is | | > 45). ? output is low when acceleration is 0.688g (axis is | | 45). these pins are push-pull. output 9 yout push-pull y-axis tilt detection output output 10 xout push-pull x-axis tilt detection output output 11 nc no internal connection 12 nc no internal connection 1 2 3 4 10 9 8 7 xout yo ut zout gnd byp v dd sda en 56 12 11 scl gnd nc nc
MMA8491Q sensors 6 freescale semiconductor, inc. 1.5 recommended app lication diagram figure 5. v dd connects to power supply and en is pulsed to ensure the accelerometer is fully functional, connect the MMA8491Q as suggested in figure 5 . ? a capacitor must be connected to the bypass pin (pin 1) to assist the internal voltage regulator. it is recommended to use a 0.1 f capacitor. the capacitor should be placed as near as possible to the bypass pin. ? the device power is supplied through the v dd line. the power supply decoupling capacitor should be placed as close as possible to the v dd pin. ? use a 1.0 or 4.7 f capacitor when the v dd and en are not tied together. ? when v dd and en are tied together, then use a 0.1 f capacitor. the 0.1 f capacitor value has been chosen to minimize the average current consumption while still maintaining an acceptable level of power supply high- frequency filtering. ? both ground pins (pins 6 and 7) must be connected to ground. ? when the i 2 c communication line is used, use a pullup resistor to connect to line sda and scl. the scl line can be driven by a push-pull driver, in which case, no pull-up resistor is necessary. if sda and scl pins are not used, then they should be tied to ground. 1 2 3 4 10 9 8 7 56 12 11 xout yout zout byp v dd 4.7 f sda scl sda en scl gnd v dd 4.7 k gnd xout yout zout nc nc 0v v dd pulsed en signal 0.1 f en v dd 4.7 k gnd - v dd connect sda/scl to gnd when i 2 c bus is not used.
MMA8491Q sensors freescale semiconductor, inc. 7 2 mechanical and electrical specifications 2.1 absolute maximum ratings table 2. maximum ratings rating symbol value unit maximum acceleration (all axes, 100 s) g max 10,000 g analog supply voltage v dd -0.3 to +3.6 v drop test d drop 1.8 m operation temperature range t agoc -40 to +85 c storage temperature range t stg -40 to +125 c table 3. esd and latchup protection characteristics rating symbol value unit human body model hbm 2000 v machine model mm 200 v charge device model cdm 500 v latchup current at t a = 85c 100 ma
MMA8491Q sensors 8 freescale semiconductor, inc. 2.2 mechanical characteristics mechanical characteristics are at v dd = 2.8v, t a = +25c, unless otherwise noted (8) (10) . 1. parameters tested 100% at final test at room temperature. 2. verified by characterization; not tested in production. 3. before board mount. 4. post-board mount offset specifications are based on a 4-layer pcb, relative to 25c. 5. all angles are based on the trip angle from static 0g to 1g; the g-values are calculated from the trip angle. 6. evaluation data: not tested in production. 7. guaranteed by design. 8. typical number is the target number, unless otherwise specified. 9. typical number is mean data. 10.all numbers are based on v dd cap = 4.7 f. table 4. mechanical characteristics parameter symbol conditions min typ max unit full-scale measurement range (2) fs 8 g sensitivity (1) so 973 1024 1075 counts/g calibrated sensitivity error (1) cse all axes, all ranges -5 5 % cross-axis sensitivity (2) cx sen die rotation included -4.2 4.2 % sensitivity temperature variation (2) tcs -40c to +85c -0.014 0.014 %/c zero-g level temperature variation (2) tco -40c to +85c -0.98 0.98 mg/c zero-g level offset accuracy (1) (3) tyoff -100 100 mg zero-g level after board mount (2) (4) tyoffpbm -120 120 mg noise (2) rms 11.5 (9) 18 mg-rms nonlinearity (2) nl 1%fs threshold / g-value (5) tdl internal threshold of output level change (from 0g reference) , g values are calculated from trip angles 25c 0.583 0.688 0.780 g -40c to +85c 0.577 0.688 0.784 threshold / tilt angle (2) (4) (5) tdl internal threshold of output level change (from 0g reference) 25c 35.6 43.5 51.3 degrees -40c to +85c 35.2 43.5 51.7 temperature range (2) t agoc -40 25 85 c
MMA8491Q sensors freescale semiconductor, inc. 9 2.3 electrical characteristics electrical characteristics are at v dd = 2.8v, t a = +25c, unless otherwise noted. (8) (13) 1. parameters tested 100% at final test at room temperature. 2. verified by characterization; not tested in production. 3. before board mount. 4. post-board mount offset specifications ar e based on a 4-layer pcb, relative to 25c. 5. all angles are based on the trip angle from static 0g to 1g; the g-values are calculated from the trip angle. 6. evaluation data: not tested in production. 7. guaranteed by design. 8. typical number is the target number unless otherwise specified. 9. typical number is mean data. 10.data is based on typical bypass cap = 100 nf. 11.data is based on max bypass cap = 470 nf. 12.over temperature -40c to 85c. 13.all numbers are based on v dd cap = 4.7 f. 14.for application connection, see figure 5 on page 6 . table 5. electrical characteristics parameter symbol conditions min typ max unit supply voltage (2) v dd 1.95 2.8 3.6 v supply current in one-shot mode i dd v dd = 2.8v, en is pulsed to v dd for 1 ms 400 (6) (9) (10) 980 (2) (11) (12) na/hz supply current in shutdown mode i sd v dd = 2.8v, en = 0 1.8 (6) (9) 68 (2) (12) na bypass capacitor at byp pin (6) c byp 70 100 470 nf high level output voltage (2) xout, yout, zout v oh i o = 500 a 0.85 * v dd v low level output voltage (2) xout, yout, zout v ol i o = 500 a 0.15 * v dd v high level input voltage (2) en v ih v dd = 2.8v 0.85 * v dd v low level input voltage (2) en v il v dd = 2.8v 0.15 * v dd v low level output voltage (7) sda v ols i o = 3 ma 0.4 v high level input voltage (7) sda, scl v ih v dd = 2.8v 0.7 * v dd v low level input voltage (7) sda, scl v il v dd = 2.8v 0.3* v dd v output source current (2) xout, yout, zout i source voltage high level v out = 0.85 x v dd , v dd = 2.8v 7.3 ma output sink current (2) xout, yout, zout i sink voltage low level v out = 0.15 x v dd , v dd = 2.8v 8.9 ma turn-on time (14) t on / t active measured from the time en = 1.95v to valid outputs 720 (6) (9) (10) 900 (2) (11) (12) s reset time (7) t rst v dd = 2.8v, the time between falling edge of en and next rising edge of en 1000 s temperature range (2) t agoc -40 25 85 c
MMA8491Q sensors 10 freescale semiconductor, inc. 2.4 i 2 c interface characteristics figure 6. i 2 c slave timing diagram table 6. i 2 c slave timing values (1) 1.all values referred to v ih(min) (0.3v dd ) and v il(max) (0.7v dd ) levels. parameter symbol i 2 c fast mode unit min max scl clock frequency f scl 0 400 khz bus-free time between stop and start condition t buf 1.3 s (repeated) start hold time t hd;sta 0.6 s repeated start setup time t su;sta 0.6 s stop condition setup time t su;sto 0.6 s sda data hold time t hd;dat 0.05 0.9 (2) 2.this device does not stretch the low period (t low ) of the scl signal. s sda setup time t su;dat 100 ns scl clock low time t low 1.3 s scl clock high time t high 0.6 s sda and scl rise time t r 20 + 0.1 c b (3) 3.c b = total capacitance of one bus line in pf. 300 ns sda and scl fall time t f 20 + 0.1 c b (3) 300 ns sda valid time (4) 4.t vd;dat = time for data signal from scl low to sda output (high or low, depending on which one is worse). t vd;dat 0.9 (2) s sda valid acknowledge time (5) 5.t vd;ack = time for acknowledgement signal from scl low to sda output (high or low, depending on which one is worse). t vd;ack 0.9 (2) s pulse width of spikes on sda and scl that must be suppressed by internal input filter t sp 050ns capacitive load for each bus line cb 400 pf v il = 0.3v dd v ih = 0.7v dd
MMA8491Q sensors freescale semiconductor, inc. 11 3 modes of operation figure 7. MMA8491Q operating modes 3.1 active mode the accelerometer subsystem is turned on at the rising edge of the en pin, and acquires one sample for each of the three axes. note that en should not be asserted before v dd reaches 1.95v. samples are acquired, converted, and compensated for zero-g offset and gain errors, and then compared to an internal threshold value of 0.688g and stored. ? if any of the x, y, z axes sample?s absolute value > this threshold , then the corresponding outputs on these axes drive logic highs. ? if any of the x, y, z axes sample?s absolute value this threshold , then the corresponding outputs on these axes drive logic lows. read register 0x00 in this stage to determine whether the sample data is ready to be read. 3.2 standby mode the device enter standby mode automatically after the previously described function (powers into shutdown mode, active mode) is accomplished. the digital output system outputs valid data, which can also be read via the i 2 c communication bus. this is the appropriate phase to read the measured data, either from the 3 push-pull logic outputs or through the i 2 c transaction. all other subsystems are turned off. these outputs are held until the MMA8491Q operation mode changes. for lower power consumption, deassert the en pin as soon as data is read (to enter shutdown mode). 3.3 next sample acquisition the MMA8491Q needs to be brought back to the active mode again by pulling en pin up to a logic 1. another option is to power down the device and start from off mode as illustrated in figure 7 . for applications where sampling intervals are greater than 30 seconds, the host can shut off the tilt sensor power after acquis ition of tilt sensor output data to conserve energy and prolong battery life. table 7. operating modes mode conditions function description digital output state off v dd = off en = don?t care device is powered off. hi-z shutdown v dd = on en = low all blocks are shut down. hi-z active v dd = on en = high all blocks are enabled. device enters standby mode automatically after data conversion. deasserted, xout = 0, yout= 0, zout = 0 standby v dd = on en = high only digital output subsystem is enabled. data is valid and available only in this stage. active, i 2 c outputs become valid en = low v dd = off active standby off* mode shutdown mode mode mode en = don?t care v dd = on en = low one sample en = high v dd = on en = high v dd = on en = high is acquired v dd = on *off mode can be entered from any state by removing the power.
MMA8491Q sensors 12 freescale semiconductor, inc. 3.4 power-up timing sequences the power-up timing sequence for mma84591q is shown in figure 8 , where v dd is powered and the en pin is activated to acquire a single sample. additional samples can be acquired by repeating the en pulse. figure 8. MMA8491Q timing sequence t on is the time between en to the end of active stage, after which the newly acquired sample data is available. 3.5 45 tilt detection the output value changes according to the absolute value of the acceleration of the MMA8491Q compared to the threshold: ? when the acceleration?s absolute value > the threshold 0.688g, the output = ?1?. ? when the acceleration?s absolute value the threshold, the output = ?0?. for example, ? when the MMA8491Q is set on a table, it senses 1g acceleration on z-axis and senses 0g on x and y axes. ? when the MMA8491Q is flipped upside down on the table, it senses -1g acceleration on z-axis and senses 0g on x and y axes. in both cases xout = 0, yout = 0, and zout = 1. v dd en off active standby shutdown shutdown t on data data available hi-z output 1, when g-value 0.688g > () 0, when g-value 0.688g () ? ? ? =
MMA8491Q sensors freescale semiconductor, inc. 13 3.6 tilt angle tilt angles can be calculated from the g-value threshold using the equation below. the tilt threshold is 0.688g, which correspo nds to 43.5. figure 9 illustrates the tilt angle threshold. ? when 0g acceleration is present on an axis, the tilt angle = 0; when 1g acceleration is present on an axis, the tilt angle = 90. ? when the tilt angle > the tilt threshold, the output for the axis is high; when the tilt angle the tilt threshold, the output for the axis is low. figure 9. MMA8491Q output is based on tilt angle and sensor g-value tilt angle g-value 1g ------------------- ?? ?? asin = horizontal reference 1g threshold = 0.688g ? threshold (g-value) = 0.688g projected g-value = tilt angle = 55 horizontal reference 1g 0.688g horizontal reference 1g 0.688g output = 1 tilt angle = 30 output = 0 tilt angle = 70 output = 1 ? ?
MMA8491Q sensors 14 freescale semiconductor, inc. 4 serial interface (i 2 c) acceleration data may be accessed through an i 2 c interface thus making the device particularly suitable for direct interfacing with a microcontroller. the MMA8491Q features three interrupt signals which indicate the tilt-sensing results on x, y, z axis respectively. the raw accelerometer data are readable via i 2 c at the same time when interrupt signal is available. the registers embedded inside the MMA8491Q are accessible through the i 2 c serial interface ( table 8 ). to enable the i 2 c interface, the en pin must be high. if either en or v dd are absent, the MMA8491Q i 2 c interface reads invalid data. the i 2 c interface may be used for communications along with other i 2 c devices. removing power from the v dd pin of the MMA8491Q does not affect the i 2 c bus. there are two signals associated with the i 2 c bus; the serial clock line (scl) and the serial data line (sda). the latter is a bidirectional line used for sending and receiving the data to/from the interface. external pullup resistors connected to v dd are expected for sda and scl. when the bus is free both the lines are high. the i 2 c interface is compliant with fast mode (400 khz, ta b l e 6 ). 4.1 i 2 c operation the transaction on the bus is started through a start condition (start) signal. a start condition is defined as a high-to-low transition on the data line while the scl line is held high. after start has been transmitted by the master, the bus is considered busy. the next byte of data transmitted after start contains the slave address in the first 7 bits, and the 8th bit tells whether the master is receiving data from the slave or tr ansmitting data to the slave. when an address is sent, each device in the system compares the first 7 bits after a start condition with it s address. if they match, then the device considers itself addressed by the master. the 9th clock pulse, following the slave address byte (and each subsequent byte), is the acknowledge (ack). the transmitter must release the sda line during the ack period. the receiver must then pull the data line low so that it remains stable low during the high period of the acknowledge clock period. a low-to-high transition on sda while scl is high is defined as a stop condition (stop). a data transfer is always terminated by a stop . a master may also issue a repeated start during a data transfer. the MMA8491Q expects repeated starts to be used to randomly read from specific registers. the MMA8491Q accelerometer standard 7-bit slave address is 0 1010101(0x55). 4.2 single byte read the transmission of an 8-bit command begins on the falling edge of scl. after the 8 clock cycles are used to send the command, note that the data returned is sent with the msb first after the data is received. figure 10 shows the timing diagram for the accelerometer 8-bit i 2 c read operation. 1. the master (or mcu) transmits a start condition (st) to the MMA8491Q, slave address (0x55), with the r/w bit set to ?0? for a write, and the MMA8491Q sends an acknowledgement. 2. then the master (or mcu) transmits the address of the register to read and the MMA8491Q sends an acknowledgement. 3. the master (or mcu) transmits a repeated start condition (sr) and then addresses the MMA8491Q (0x1d) with the r/ w bit set to ?1? for a read from the previously selected register. 4. the slave then acknowledges and transmits the data from the requested register. 5. the master does not acknowledge (nak) the transmitted data, but transmits a stop condition to end the data transfer. table 8. serial interface pins pin description scl i 2 c serial clock sda i 2 c serial data table 9. i 2 c device address sequence command [7:1] device address [7:1] device address [0] r/w [7:0] 8-bit final value read 01010101 0x55 1 0xab write 01010101 0x55 0 0xaa
MMA8491Q sensors freescale semiconductor, inc. 15 figure 10. single byte read 4.3 multiple byte read when performing a multibyte read or ?burst read?, the mma849 1q automatically increments the received register address commands after a read command is received. therefore, after following the steps of a single byte read, multiple bytes of data can be read from sequential registers after each MMA8491Q acknowledgment (ak) is received, until a no acknowledge (nak) occurs from the master, followed by a stop condition (sp) signaling an end of transmission. continued . . . figure 11. multiple byte read legend st: start condition sp: stop condit ion nak: no acknowledge w: write = 0 sr: repeated start condition ak: acknowledge r: read = 1 master st device address[7:1] w register address[7:0] sr device address[7:1] r nak sp slave ak ak ak data[7:0] master st device address[7:1] w register address[7:0] sr device address[7:1] r ak slave ak ak ak data[7:0] master ak ak nak sp slave data[7:0] data[7:0] data[7:0]
MMA8491Q sensors 16 freescale semiconductor, inc. 5 register descriptions 5.1 register address map 5.2 register bit map table 10. register address map (1)(2) 1. register contents are preserved w hen en pin is set high after sampling. 2. register contents are reset when en pin is set low. name type register address auto-increment address (3) 3. auto-increment is the i 2 c feature that the i 2 c read address is automatically updated after each read. auto-increment addresses which are not a simple increment are highlighted in bold . the auto-increment addressing is only enabl ed when device register s are read using i 2 c burst read mode. therefore the internal stor age of the auto-increment address is cl eared whenever a stop-bit is detected. default comment status r 0x00 0x01 0x00 read time status out_x_msb r 0x01 0x02 output [7:0] are 8 msbs of the 14-bit sample out_x_lsb r 0x02 0x03 output [7:2] are the 6 lsb of 14-bit sample out_y_msb r 0x03 0x04 output [7:0] are 8 msbs of the 14-bit sample out_y_lsb r 0x04 0x05 output [7:2] are the 6 lsb of 14-bit sample out_z_msb r 0x05 0x06 output [7:0] are 8 msbs of the 14-bit sample out_z_lsb r 0x06 0x00 output [7:2] are the 6 lsb of 14-bit sample table 11. register bit map address offset name 7 6 5 4 3 2 1 0 0x00 status r 0 0 0 0 zyxdr zdr ydr xdr 0x01 out_x_msb r xd[13:6] 0x02 out_x_lsb r xd[5:0] 0 0 0x03 out_y_msb r yd[13:6] 0x04 out_y_lsb r yd[5:0] 0 0 0x05 out_z_msb r zd[13:6] 0x06 out_z_lsb r zd[5:0] 0 0
MMA8491Q sensors freescale semiconductor, inc. 17 5.3 data registers 5.3.1 0x00 status register register 0x00 reflects the real-time status information of the x, y, and z sample data. the data read bits (zyxdr, zdr, ydr, xdr) are set when samples are taken and ready to be read. table 12. status register field description zyxdr x, y, z-axis new data ready (and available) ?zyxdr signals that a new sample for all channels is available. ? zyxdr is cleared when the high-bytes of the acceleration data (out_x_msb, out_y_msb, out_z_msb) of all channels are read. 0: no new set of data ready (default value) 1: a new set of data is ready zdr z-axis new data ready (and available) ?zdr is set whenever a new acceleration sample related to the z-axis is generated. ? zdr is cleared anytime out_z_msb register is read. 0: no new z-axis data is ready (default value) 1: a new z-axis data is ready ydr y-axis new data ready (and available) ?ydr is set whenever a new acceleration samp le related to the y-axis is generated. ? ydr is cleared anytime out_y_msb register is read. 0: no new y-axis data ready (default value) 1: a new y-axis data is ready xdr x-axis new data ready (and available) ?xdr is set whenever a new acceleration samp le related to the x-axis is generated. ? xdr is cleared anytime out_x_msb register is read. 0: no new x-axis data ready (default value) 1: a new x-axis data is ready
MMA8491Q sensors 18 freescale semiconductor, inc. 5.3.2 accelerometer data registers (0x01?0x06) these registers contain the x-axis, y-axis, and z-axis14-bit output sample data (expressed as 2's complement numbers). ? out_x_msb, out_x_lsb, out_y_msb, out_y_lsb, out_z_msb, and out_z_lsb are stored in the auto- incrementing address range of 0x01 ? 0x06. ? the lsb registers can only be read immediately following the read access of the corresponding msb register. a random read access to the lsb registers is not possible. ? reading the msb register and then the lsb register in sequence ensures that both bytes (lsb and msb) belong to the same data sample, even if a new data sample arrives between reading the msb and the lsb byte. ? the accelerometer data registers should be read only after the status register has confirmed that new data on all axes is available. 5.4 accelerometer output conversion table 13. out_x_msb: x_msb register (0x01, read-only) bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 xd[13:7] table 14. out_x_lsb: x_lsb register (0x02, read-only) bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 xd[5:0] 0 0 table 15. out_y_msb: y_msb register (0x03, read-only) bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 yd[13:6] table 16. out_y_lsb: y_lsb register (0x04, read-only) bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 yd[5:0] 0 0 table 17. out_z_msb: z_msb register (0x05, read-only) bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 zd[13:6] table 18. out_z_lsb: z_lsb register (0x06, read-only) bit 7bit 6bit 5bit 4bit 3bit 2bit 1bit 0 zd[5:0] 0 0 table 19. accelerometer output data 14-bit data range 8g (1 mg/count) 01 1111 1111 1111 +8.000g 01 1111 1111 1110 +7.998g ? ... 00 0000 0000 0000 0.000g 11 1111 1111 1111 -0.001g ... ... 10 0000 0000 0001 -7.998g 10 0000 0000 0000 -8.000g
MMA8491Q sensors freescale semiconductor, inc. 19 6 mounting guidelines surface mount printed circuit board (pcb) layout is a critical portion of the total design. the footprint for the surface mount packages must be the correct size to ensure proper solder connection interface between the pcb and the package. with the correct footprint, the packages will self-align when subjected to a solder reflow process. the purpose is to minimize the stres s on the package after board mounting. the MMA8491Q accelerometers use the qfn package. this section describes suggested methods of soldering and mounting these devices to the pcb for consumer applications. 6.1 overview of soldering considerations the information provided here is based on experiments executed on qfn devices. they do not represent exact conditions present at a customer site. hence, information herein should be used as guidance only and process and design optimizations are recommended to develop an application specific solution. it should be noted that with the proper pcb footprint and solder stencil designs, the package will self-align during the solder reflow process. 6.2 halogen content this package is designed to be halogen free, exceeding most industry and customer standards. halogen free means that no homogeneous material within the assembly package shall contain chlorine (cl) in excess of 700 ppm or 0.07% weight/weight or bromine (br) in excess of 900 ppm or 0.09% weight/weight. 6.3 pcb mounting recommendations 1. do not solder down exposed pad (ep) under the package to minimize board mounting stress impact to product performance. 2. pcb landing pad is 0.675 mm x 0.325 mm as shown in figure 12 . 3. solder mask opening = pcb land pad edge + 0.2 mm larger all around. 4. stencil opening size is 0.625 mm x 0.3 mm. 5. stencil thickness is 100 or 125 m. 6. the solder mask should not cover any of the pcb landing pads, as shown in figure 12 . 7. no additional via nor metal pattern underneath package on the top of the pcb layer. 8. do not place any components or vias within 2 mm of the package land area. this may cause additional package stress if it is too close to the package land area. 9. signal traces connected to pads should be as symmetric as possible. put dummy traces on nc pads, to have same length of exposed trace for all pads. 10. use a standard pick and place process and equipment. do not use a hand soldering process. 11. customers are advised to be cautious about the proximity of screw down holes to the sensor, and the location of any press fit to the assembled pcb when in an enclosure. it is important that the assembled pcb remain flat after assembly to keep electronic operation of the device optimal. 12. the pcb should be rated for the multiple lead-free reflow condition with max 260c temperature. 13. freescale sensors are compliant with restrictions on hazardous substances (rohs), having halide free molding compound (green) and lead-free terminations. these terminations are compatible with tin-lead (sn-pb) as well as tin- silver-copper (sn-ag-cu) solder paste soldering processes. reflow profiles applicable to those processes can be used successfully for soldering the devices.
MMA8491Q sensors 20 freescale semiconductor, inc. figure 12. pcb footprint guidelines symbol description value (mm) a pitch 0.650 b landing pad width 0.325 c landing pad length 0.675 d1 solder mask pattern width 1.175 d2 solder mask pattern length 0.875 e1 solder mask pattern width 0.875 e2 solder mask pattern length 2.475 f i/o pads extended length 3.8 g i/o pads extended length 3.8

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MMA8491Q sensors freescale semiconductor, inc. 21 7 tape and reel 7.1 tape dimensions figure 13. mechanical dimensions 7.2 label and device orientation MMA8491Q is oriented on the tape as illustrated in figure 14 . the front side dot marked on the device indicates pin 1. figure 14. tape and reel orientation measurements are in millimeters. direction to unreel MMA8491Q pin 1 bar code label side of reel
MMA8491Q sensors 22 freescale semiconductor, inc. 8 package dimensions figure 15. case 2169-02, issue x1, 12-lead qfn?page 1
MMA8491Q sensors freescale semiconductor, inc. 23 figure 16. case 2169-02, issue x1, 12-lead qfn?page 2
MMA8491Q sensors 24 freescale semiconductor, inc. figure 17. case 2169-02, issue x1, 12-lead qfn?page 3
MMA8491Q sensors 25 freescale semiconductor, inc. 9 revision history table 20. revision history revision number revision date description of changes 1 10/2012 ? initial release 2 11/2012 ? characterization data verified to be complete and final
document number: MMA8491Q rev 2.0 11/2012 how to reach us: home page: freescale.com web support: freescale.com/support information in this document is provided solely to enable system and software implementers to use freescale products. there are no express or implied copyright licenses granted hereunder to design or fabricate any integrated circuits based on the information in this document. freescale reserves the right to make changes without further notice to any products herein. freescale makes no warranty, representation, or guarantee regarding the suitability of its products for any particular purpose, nor does freescale assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation consequential or incidental damages. ?typical? parameters that may be provided in freescale data sheets 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 does not convey any license under its patent rights nor the rights of others. freescale sells products pursuant to standard terms and conditions of sale, which can be found at the following address: freescale.com/salestermsandconditions. freescale, the freescale logo, altivec, c-5, codetest, codewarrior, coldfire, c-ware, energy efficient solutions logo, kinetis, mobilegt, powerquicc, processor expert, qoriq, qorivva, starcore, symphony, and vortiqa are trademarks of freescale semiconductor, inc., reg. u.s. pat. & tm. off. airfast, beekit, beestack, coldfire+, corenet, flexis, magniv, mxc, platform in a package, qoriq qonverge, quicc engine, ready play, safeassure, smartmos, turbolink, vybrid, and xtrinsic are trademarks of freescale semiconductor, inc. all other product or service names are the property of their respective owners. ? 2012 freescale semiconductor, inc.

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