LSM303DLH datasheet(17/47 Pages) STMICROELECTRONICS

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LSM303DLH

Terminology

Doc ID 16941 Rev 1

17/47

Terminology

4.1

Linear acceleration sensitivity

Linear acceleration sensitivity describes the gain of the accelerometer sensor and can be

determined e.g. by applying 1

g acceleration to it. Because the sensor can measure DC

accelerations, this can be done easily by pointing the selected axis towards the ground,

noting the output value, rotating the sensor 180 degrees (pointing towards the sky) and

noting the output value again. By doing so, a ±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

over time. The sensitivity tolerance describes the range of sensitivities of a large number of

sensors.

4.2

Zero-

g level

Zero-

g level Offset (LA_TyOff) describes the deviation of an actual output signal from the

ideal output signal if no linear acceleration is present. A sensor in a steady state on a

horizontal surface will measure 0 g on both the X and Y axes, whereas the Z axis will

measure 1

g. Ideally, the output is 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 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. Offset changes

little over temperature; see “Linear acceleration zero-

g level change vs temperature”

(LA_TCOff) in

Table 3. The Zero-g level tolerance (TyOff) describes the standard deviation

of the range of Zero-

g levels of a group of sensors.

4.3

Sleep-to-wakeup

The “sleep-to-wakeup” function, in conjunction with low-power mode, allows further

reduction of system power consumption and the development of new smart applications.

The LSM303DLH may be set to a low-power operating mode, characterized by lower date

rate refreshing. In this way the device, even if sleeping, continues sensing acceleration and

generating interrupt requests.

When the sleep-to-wakeup function is activated, the LSM303DLH is able to automatically

wake up as soon as the interrupt event has been detected, increasing the output data rate

and bandwidth. With this feature the system may be efficiently switched from low-power

mode to full-performance depending on user-selectable positioning and acceleration events,

thus ensuring power-saving and flexibility.

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