MMA8652FC datasheet(13/65 Pages) NXP

13 / 65 page

MMA8652FC

Sensors

Freescale Semiconductor, Inc.

Functionality

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

2C interface with embedded logic 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

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Single/double tap with directional information (one channel)

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Motion detection with directional information or Freefall (one 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 (one channel)

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

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

Tap, Orientation, Transient, FIFO, Auto-WAKE)

All functionality is available in ±2 g, ±4 g or ±8 g 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 three volatile 8-bit registers (OFF_X, OFF_Y,

OFF_Z).

5.2

8-bit or 12-bit

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

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

these three registers (and ignore the OUT_X/Y/Z_LSB registers). To 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 ±2 g, the measurement range is –2 g to +1.999 g, and each count corresponds to (1/1024) g

(0.98 mg) at 12-bit resolution.

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

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(1.96 mg) at 12-bit resolution.

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

(3.9 mg) at 12-bit 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 ±2 g (1 mg/LSB)

Range ±4 g (2 mg/LSB)

Range ±8 g (4 mg/LSB)

0111 1111 1111

1.999 g

+3.998 g

+7.996 g

0111 1111 1110

1.998 g

+3.996 g

+7.992 g

……

…

0000 0000 0001

0.001 g

+0.002 g

+0.004 g

0000 0000 0000

0.0000 g

1111 1111 1111

–0.001 g

–0.002 g

–0.004 g

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