LIS35DETR datasheet(14/39 Pages) STMICROELECTRONICS

14 / 39 page

Mechanical and electrical specifications

LIS35DE

14/39

Doc ID 15594 Rev 1

2.5

Terminology

2.5.1

Sensitivity

Sensitivity describes the gain of the sensor and can be determined e.g. by applying 1g

acceleration to it. As the sensor can measure DC accelerations this can be done easily by

pointing the axis of interest towards the center of the Earth, noting the output value, rotating

the sensor by 180 degrees (point to the sky) and noting the output value again. By doing so,

±1g acceleration is applied to the sensor. Subtracting the larger output value from the

smaller one and dividing the result by 2 leads to the actual sensitivity of the sensor. This

value changes very little over temperature and also very little over time. The Sensitivity

Tolerance describes the range of Sensitivities of a large population of sensor.

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

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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