LSM320HAY30 datasheet(15/42 Pages) STMICROELECTRONICS

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LSM320HAY30

Functionality and terminology

Doc ID 16917 Rev 1

15/42

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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