MMA8652FC datasheet(13/77 Pages) FREESCALE

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MMA8652FC

Sensors

Freescale Semiconductor, Inc.

Functionality

The MMA8652FC is a low-power, digital output 3-axis linear accelerometer with a I

2C interface, and has embedded logic that is

used to detect events and notify an external microprocessor over interrupt lines.

•

8-bit or 12-bit data, high-pass filtered data, 8-bit or 12-bit configurable 32-sample FIFO

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Four different oversampling options that allow for the optimum resolution vs. current consumption trade-off to be made for a

given application

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Low power and auto-WAKE/SLEEP modes for reducing current consumption

•

Single/double tap with directional information (1 channel)

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Motion detection with directional information or Freefall (1 channel)

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Transient/jolt detection based on a high-pass filter, with a settable threshold for detecting the change in acceleration above

a threshold with directional information (1 channel)

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Flexible user-configurable portrait landscape detection algorithm, for addressing many use cases for screen orientation

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Two independent interrupt output pins that are programmable among 7 interrupt sources (Data Ready, Motion/Freefall, Tap,

Orientation, Transient, FIFO and Auto-WAKE)

All functionality is available in 2g, 4g or 8g dynamic measurement ranges. There are many configuration settings for enabling all of

the different functions. Separate application notes are available to help configure the device for each embedded functionality.

5.1

Device calibration

The device is factory calibrated for sensitivity and Zero-g offset for each axis. The trim values are stored in Non-Volatile Memory

(NVM). On power-up, the trim parameters are read from NVM and applied to the circuitry. In normal use, further calibration in the

end application is not necessary. However, the MMA8652FC allows you to adjust the offset for each axis after power-up, by

changing the default offset values. The user offset adjustments are stored in 3 volatile 8-bit registers (OFF_X, OFF_Y, OFF_Z).

5.2

8-bit or 12-bit data

The measured acceleration data is stored in the following registers as 2’s complement 12-bit numbers:

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OUT_X_MSB, OUT_X_LSB

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OUT_Y_MSB, OUT_Y_LSB

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OUT_Z_MSB, OUT_Z_LSB

The most significant 8-bits of each axis are stored in OUT_X (Y, Z)_MSB, so applications needing only 8-bit results can use these

3 registers (and ignore the OUT_X/Y/Z_LSB registers). To do this (use only 8-bit results), the F_READ bit in CTRL_REG1 must

be set. When the F_READ bit is cleared, the fast read mode is disabled.

•

When the full-scale is set to 2g, the measurement range is -2g to +1.999g, and each count corresponds to (1/1024)g

(0.98mg) at 12-bits resolution.

•

When the full-scale is set to 4g, the measurement range is -4g to +3.998g, and each count corresponds to (1/512)g

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(1.96mg) at 12-bits resolution.

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When the full-scale is set to 8g, the measurement range is -8g to +7.996g, and each count corresponds to (1/256)g (3.9

mg) at 12-bits resolution.

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If only the 8-bit results are used, then the resolution is reduced by a factor of 16.

For more information about the data manipulation between data formats and modes, see application note AN4083, Data

Manipulation and Basic Settings for Xtrinsic MMA865xFC Accelerometers. There is a device driver available that can be used

with the Sensor Toolbox demo board (LFSTBEB865xFC) with this application note.

Table 8. Accelerometer 12-bit output data

12-bit data

Range ±2g (1 mg)

Range ±4g (2 mg)

Range ±8g (4 mg)

0111 1111 1111

1.999g

+3.998g

+7.996g

0111 1111 1110

1.998g

+3.996g

+7.992g

……

…

0000 0000 0001

0.001g

+0.002g

+0.004g

0000 0000 0000

0.0000g

1111 1111 1111

-0.001g

-0.002g

-0.004g

……

…

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