LIS302DL datasheet(15/42 Pages) STMICROELECTRONICS

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LIS302DL

Mechanical and electrical specifications

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2.5.2

Zero-g level

Zero-g level Offset (Off) describes the deviation of an actual output signal from the ideal

output signal if there is no acceleration present. A sensor in a steady state 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

00h, 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 to a precise 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. Offset changes little over temperature,

see “Zero-g level change vs. temperature”. The Zero-g level of an individual sensor is stable

over lifetime. The Zero-g level tolerance describes the range of Zero-g levels of a population

of sensors.

2.5.3

Self test

Self Test allows to check the sensor functionality without moving it. The Self Test function is

off when the self-test bit of CTRL_REG1 (control register 1) is programmed to ‘0‘. When the

self-test bit of ctrl_reg1 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 is 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 inside

Table 3, than the sensor is

working properly and the parameters of the interface chip are within the defined

specification.

2.5.4

Click and double click recognition

The Click and Double Click recognition functions help to create man-machine interface with

little software overload. The device can be configured to output an interrupt signal on

dedicated pin when tapped in any direction.

If the sensor is exposed to a single input stimulus it generates an interrupt request on inertial

interrupt pin (INT1 and/or INT2). A more advanced feature allows to generate and interrupt

request when a “double click” with programmable time between the two events enabling a

“mouse button like” use.

This function can be fully programmed by the user in terms of expected amplitude and

timing of the stimuli.

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