LIS3DHTR datasheet(15/42 Pages) STMICROELECTRONICS

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LIS3DH

Terminology and functionality

Doc ID 17530 Rev 1

15/42

Terminology and functionality

3.1

Terminology

3.1.1

Sensitivity

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

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 (pointing to the sky) and noting the output value again. By doing

so, ±1 g 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 time. The sensitivity tolerance describes

the range of Sensitivities of a large population of sensors.

3.1.2

Zero-g level

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

output signal if no acceleration is present. A sensor in a steady state on a horizontal surface

measure 0 g in X axis and 0 g in Y axis whereas the Z axis measure 1 g. 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 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 tolerance (TyOff) describes the standard

deviation of the range of Zero-g levels of a population of sensors.

3.2

Functionality

3.2.1

Normal mode, low power mode

LIS3DH provides two different operating modes respectively reported as normal mode and

low power mode. While normal mode guarantees high resolution, low power mode reduces

further the current consumption.

The table below reported summarizes how to select the operating mode.

Table 9.

Operating mode selection

CTRL_REG1[3]

(LPen bit)

CTRL_REG4[3]

(HR bit)

Operating mode

Low power mode

Normal mode

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