lis3dsh STMicroelectronics, lis3dsh Datasheet - Page 17

• Manufacturer Part Number: lis3dsh
• Description: Mems Digital Output Motion Sensor Ultra Low-power High Performance Three-axis “nano” Accelerometer
• Manufacturer: STMicroelectronics

LIS3DSH
3.5
3.5.1
3.5.2
3.6
3.6.1
3.7
Terminology
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.
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
measures 0 g in X axis and 0 g in 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 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 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
Self-test
Self-test allows to check the sensor functionality without moving it. The self-test function is
off when the self-test bit (ST) is programmed to ‘0‘. When the self-test bit is programmed to
‘1’, an actuation force is applied to the sensor, simulating a definite input acceleration. In this
case the sensor outputs exhibit a change in their DC levels which are related to the selected
full-scale through the device sensitivity. When self-test is activated, the device output level is
given by the algebraic sum of the signals produced by the acceleration acting on the sensor
and by the electrostatic test-force. If the output signals change within the amplitude
specified in
chip are within the defined specifications.
Sensing element
A proprietary process is used to create a surface micro-machined accelerometer. The
technology allows to carry out suspended silicon structures which are attached to the
substrate in a few points called anchors and are free to move in the direction of the sensed
acceleration. To be compatible with the traditional packaging techniques, a cap is placed on
top of the sensing element to avoid blocking the moving parts during the moulding phase of
the plastic encapsulation.
Table
3, then the sensor is working properly and the parameters of the interface
Doc ID 022405 Rev 1
Mechanical and electrical specifications
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