BMA253
Data sheet
Page 20
4.4 Self-test
This feature permits to check the sensor functionality by applying electrostatic forces to the
sensor core instead of external accelerations. By actually deflecting the seismic mass, the
entire signal path of the sensor can be tested. Activating the self-test results in a static offset of
the acceleration data; any external acceleration or gravitational force applied to the sensor
during active self-test will be observed in the output as a superposition of both acceleration and
self-test signal.
Before the self-test is enabled the g-range should be set to 8 g.The self-test is activated
individually for each axis by writing the proper value to the (0x32) self_test_axis bits (´01b´ for x-
axis, ´10b´ for y-axis, ´11b´ for z-axis, ´00b´ to deactivate self-test). It is possible to control the
direction of the deflection through bit (0x32) self_test_sign. The excitation occurs in negative
(positive) direction if (0x32) self_test_sign = ´0b´ (´1b´). The amplitude of the deflection has to
be set high by writing (0x32) self_test_amp=´1b´. After the self-test is enabled, the user should
wait 50ms before interpreting the acceleration data.
In order to ensure a proper interpretation of the self-test signal it is recommended to perform the
self-test for both (positive and negative) directions and then to calculate the difference of the
resulting acceleration values. Table 6 shows the minimum differences for each axis. The
actually measured signal differences can be significantly larger.
Table 6: Self-test difference values
x-axis signal
y-axis signal
z-axis signal
resulting minimum
difference signal
800 mg
800 mg
400 mg
It is recommended to perform a reset of the device after a self-test has been performed. If the
reset cannot be performed, the following sequence must be kept to prevent unwanted interrupt
generation: disable interrupts, change parameters of interrupts, wait for at least 50ms, enable
desired interrupts.
BST-BMA253-DS000-01 | Revision 1.0 | August 2015
Bosch Sensortec
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Note: Specifications within this document are subject to change without notice.
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