Datasheet

Sensors
10 NXP Semiconductors
MMA8452Q
3 Terminology
3.1 Sensitivity
The sensitivity is represented in counts/g. In 2 g mode the sensitivity is 1024 counts/g. In 4 g mode the sensitivity is
512 counts/g and in 8 g mode the sensitivity is 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 0 g in X-axis and 0 g in Y-axis whereas the Z-axis will measure 1 g. The
output is ideally in the middle of the dynamic range of the sensor (content of OUT registers 0x00, data expressed as 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
exposing it to extensive mechanical stress.
3.3 Self-test
Self-test checks the transducer functionality without 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. When self-test is activated, 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.