H3LIS331DL Datasheet, PDF (14/38 Pages) STMicroelectronics – MEMS motion sensor: low-power high-g 3-axis digital accelerometer

Mechanical and electrical specifications
H3LIS331DL
2.5
2.5.1
2.5.2
2.5.3
Terminology
Sensitivity
Sensitivity describes the gain of the 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 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 time. The sensitivity tolerance describes the
range of sensitivities of a large population of sensors.
Zero-g level
The 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 measures 0 g for the X-axis and 0 g for the Y-axis whereas the Z-axis measures 1 g.
The output is ideally in the middle of the dynamic range of the sensor (content of OUT
registers 00h, data expressed as two’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 can slightly change after mounting the sensor onto a printed
circuit board or exposing it to extensive mechanical stress. Offset changes little over
temperature, refer to “Zero-g level change vs. temperature” (see TCOff in Table 3). The
zero-g level tolerance (TyOff) describes the standard deviation of the range of zero-g levels
of a population of sensors.
Sleep-to-wakeup
The “sleep-to-wakeup” function, in conjunction with low-power mode, allows to further
reduce the system power consumption and develop new smart applications.
The H3LIS331DL may be set in a low-power operating mode, characterized by lower date
rate refreshments. In this way the device, even if sleeping, continues to sense acceleration
and generate interrupt requests.
When the “sleep-to-wakeup” function is activated, the H3LIS331DL 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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