LSM320HAY30 Datasheet, PDF (15/42 Pages) STMicroelectronics – MEMS motion sensor module: 3D digital accelerometer and 2D pitch and yaw analog gyroscope

LSM320HAY30
Functionality and terminology
of OUT registers 00h, data expressed as 2’s complement number). A deviation from the
ideal value in this case is called Zero-g offset.
Offset is to some extent a result of stress to 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.
Zero-g level offset changes little over temperature, see “Zero-g level change vs.
temperature” (LA_TCOff) in Table 2. The Zero-g level tolerance (LA_TyOff) describes the
standard deviation of the range of Zero-g levels of a group of sensors.
Zero-rate level
Angular rate zero-rate level (AR_Zrl) describes the actual angular rate output signal if there
is no angular rate present. Zero-rate level of precise MEMS sensors is, to some extent, a
result of stress to the sensor and therefore zero-rate level can slightly change after mounting
the sensor onto a printed circuit board or after exposing it to extensive mechanical stress.
This value changes very little over temperature and time.
4.4
Self-test
Linear acceleration self-test
Self-test allows the checking of sensor functionality without moving it. The self-test function
is off when the self-test bit (ST) of LA_CTRL_REG4 (control register 4) is programmed to ‘0‘.
When the self-test bit of LA_CTRL_REG4 is programmed to ‘1‘ an actuation force is applied
to the sensor, simulating a definite input 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. If the output signals change within the amplitude specified in
Table 2, then the sensor is working properly and the parameters of the interface chip are
within the defined specifications.
Angular rate self-test
Self-test allows testing of the mechanical and electric parts of the sensor, permitting the
seismic mass to be moved by means of an electrostatic test-force. The self-test function is
off when the ARST pin is connected to GND. When the ARST pin is tied to Vdd and ARPD is
tied to GND (see Table 5), an actuation force is applied to the sensor, emulating a definite
Coriolis force. In this case the sensor output exhibits a voltage change in its DC level which
is also dependent on the supply voltage. When ST is active, the device output level is given
by the algebraic sum of the signals produced by the velocity acting on the sensor and by the
electrostatic test-force. If the output signals change within the amplitude specified in
Table 2, then the mechanical element is working properly and the parameters of the
interface chip are within the defined specifications.
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