AIS328DQ Datasheet, PDF (14/43 Pages) STMicroelectronics – High-performance ultra low-power 3-axis accelerometer

Mechanical and electrical specifications
AIS328DQ
Note:
1. Design guarantee; characterization done at 1500 g/0.5 ms, 3000 g/0.3 ms, 10000 g/0.1 ms; tests under
these conditions have passed successfully.
Supply voltage on any pin should never exceed 4.0 V.
This is a mechanical shock sensitive device, improper handling can cause permanent
damage to the part.
This is an ESD sensitive device, improper handling can cause permanent damage to
the part.
2.5
2.5.1
2.5.2
2.5.3
14/43
Terminology
Sensitivity
Sensitivity describes the gain of the sensor and can be determined, for example, by applying
a 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, 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 also over time. The sensitivity
tolerance describes the range of sensitivity 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 on the X-axis and 0 g on the Y-axis, whereas the Z-axis measures 1 g. The
output is ideally in the center of the dynamic range of the sensor (the content of the OUT
registers is 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 “Zero-g level change vs. temperature” 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.
Self-test
Self-test allows the sensor functionality to be tested without moving it. The self-test function
is off when the self-test bit (ST) of CTRL_REG4 (control register 4) is programmed to ‘0‘.
When the self-test bit of CTRL_REG4 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 Table 3, then the sensor is
working properly and the parameters of the interface chip are within the defined
specifications.
Doc ID 18160 Rev 3