MMA8652FC datasheet(11/77 Pages) FREESCALE

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MMA8652FC

Sensors

Freescale Semiconductor, Inc.

Terminology

3.1

Sensitivity

The sensitivity is represented in counts/g.

•

In 2g mode, sensitivity = 1024 counts/g.

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In 4g mode, sensitivity = 512 counts/g.

•

In 8g mode, sensitivity = 256 counts/g.

3.2

Zero-g offset

Zero-g Offset (TyOff) describes the deviation of an actual output signal from the ideal output signal if the sensor is stationary. A

sensor stationary on a horizontal surface will measure 0g in X-axis and 0g in Y-axis, whereas the Z-axis will measure 1g. The

output is ideally in the middle of the dynamic range of the sensor (content of OUT Registers 0x00, data expressed as a 2's

complement number). A deviation from ideal value in this case is called Zero-g offset.

Offset is to some extent a result of stress on the MEMS sensor, and therefore the offset can slightly change after mounting the

sensor onto a printed circuit board or after exposing it to extensive mechanical stress.

3.3

Self-Test

Self-Test can be used to verify the transducer and signal chain functionality without the need to apply external mechanical

stimulus.

When Self-Test is activated:

•

An electrostatic actuation force is applied to the sensor, simulating a small acceleration. In this case, the sensor outputs will

exhibit a change in their DC levels which, are related to the selected full scale through the device sensitivity.

•

The device output level is given by the algebraic sum of the signals produced by the acceleration acting on the sensor and by

the electrostatic test-force.

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