LSM303DLMTR datasheet(13/38 Pages) STMICROELECTRONICS

13 / 38 page

LSM303DLM

Terminology

Doc ID 018725 Rev 1

13/38

Terminology

4.1

Linear acceleration sensitivity

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

determined by applying 1

g acceleration to it. As 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 to 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 steady-state on a

horizontal surface measures 0 g on both the X and Y axes, whereas the Z axis measures 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 LSM303DLM may be set to a low-power operating mode, characterized by lower data

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 LSM303DLM 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,

therefore ensuring power-saving and flexibility.

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