3-AXIS ACCELEROMETER DIGITAL I/F

BMA250

Manufacturer Part NumberBMA250
Description3-AXIS ACCELEROMETER DIGITAL I/F
ManufacturerBosch Sensortec
Series-
BMA250 datasheets
 

Specifications of BMA250

Featured ProductBMA250 - Digital, Triaxial Acceleration SensorAxisX, Y, Z
Acceleration Range±2g, 4g, 8g, 16gSensitivity256LSB/g, 128LSB/g, 64LSB/g, 16LSB/g
Voltage - Supply1.62 V ~ 3.6 VOutput TypeI²C™, SPI™
Bandwidth8Hz ~ 1kHzInterfaceI²C, SPI
Mounting TypeSurface MountPackage / Case12-VQFN
Lead Free Status / Rohs StatusLead free / RoHS CompliantFor Use With828-1024 - BMA250 DAUGHTERCARD FOR DEV KIT
Other names828-1023-2  
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Page 18/74

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BMA250
Bosch Sensortec
Data sheet
4.5 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.
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 positive (negative) direction if (0x32) self_test_sign = ´0b´ (´1b´).
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 10 shows the minimum differences for each axis. The
actually measured signal differences can be significantly larger.
Table 10: Self-test difference values
x-axis signal
y-axis signal
z-axis signal
resulting
minimum
+0.8 g
+0.8 g
+0.4 g
difference signal
It is recommended to perform a reset of the device after self-test. 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 600 s, enable desired
interrupts.
4.6 Offset compensation
Offsets in measured signals can have several causes but they are always unwanted and
disturbing in many cases. Therefore, the BMA250 offers an advanced set of four digital offset
compensation methods which are closely matched to each other. These are slow, fast, and
manual compensation, and inline calibration.
The compensation is performed for unfiltered and filtered data independently. It is done by
adding a compensation value to the acceleration data coming from the ADC. The result of this
computation is saturated if necessary to prevent any overflow errors (the smallest or biggest
possible value is set, depending on the sign). However, the public registers used to read and
write compensation values have only a width of 8 bits.
An overview of the offset compensation principle is given in figure 4:
Rev. 1.0
Page 18 / not for publishing
03 March 2011
© Bosch Sensortec GmbH reserves all rights even in the event of industrial property rights. We reserve all rights of disposal such
as copying and passing on to third parties. BOSCH and the symbol are registered trademarks of Robert Bosch GmbH, Germany.
Note: Specifications within this document are subject to change without notice.