LIS2DH datasheet(16/50 Pages) STMICROELECTRONICS

16 / 50 page

Mechanical and electrical specifications

LIS2DH

16/49

Doc ID 022516 Rev 1

2.6

Terminology and functionality

Terminology

2.6.1

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.

2.6.2

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

will measure 0 g in X axis and 0 g in Y axis whereas the Z axis will 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.

Functionality

2.6.3

High resolution, Normal mode, Low power mode

The LIS2DH provides three different operating modes respectively reported as High

resolution mode, Normal mode and Low power mode.

The table below reported summarizes how to select among the different operating modes.

Table 9.

Operating mode selection

Operating mode

CTRL_REG1[3]

(LPen bit)

CTRL_REG4[3]

(HR bit)

BW [Hz]

Turn-on

time [ms]

So @ ±2g

[mg/digit]

Low power mode (8

bit data output)

ODR/2

Normal mode(10 bit

data output)

ODR/2

1.6

High resolution (12

bit data output)

ODR/9

7/ODR

Not allowed

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