BMA250 Bosch Sensortec, BMA250 Datasheet - Page 21

• Manufacturer Part Number: BMA250
• Description: 3-AXIS ACCELEROMETER DIGITAL I/F
• Manufacturer: Bosch Sensortec
• Series: -r

Specifications of BMA250

• Featured Product: BMA250 - Digital, Triaxial Acceleration Sensor
• Axis: X, Y, Z
• Acceleration Range: ±2g, 4g, 8g, 16g
• Sensitivity: 256LSB/g, 128LSB/g, 64LSB/g, 16LSB/g
• Voltage - Supply: 1.62 V ~ 3.6 V
• Output Type: I²C™, SPI™
• Bandwidth: 8Hz ~ 1kHz
• Interface: I²C, SPI
• Mounting Type: Surface Mount
• Package / Case: 12-VQFN
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• For Use With: 828-1024 - BMA250 DAUGHTERCARD FOR DEV KIT
• Other names: 828-1023-2

4.6.2 Fast compensation
Fast compensation is a one-shot process by which the compensation value is set in such a way
that when added to the raw acceleration, the resulting acceleration value of each axis equals
the target value.
The algorithm in detail: An average of 16 consecutive acceleration values is computed and the
difference between target value and computed value is written to (0x38, 0x39, 0x3A)
offset_filt_x/y/z or (0x3B, 0x3C, 0x3D) offset_unfilt_x/y/z The public registers (0x38, 0x39, 0x3A)
offset_filt_x/y/z and (0x3B, 0x3C, 0x3D) offset_unfilt_x/y/z are updated with the contents of the
internal registers (using saturation if necessary) and can be read by the user.
Fast compensation is triggered for each axis individually by setting the (0x36) cal_trigger bits as
shown in table 13:
The register (0x36) cal_trigger keeps its non-zero value while the fast compensation procedure
is running. Slow compensation is blocked as long as fast compensation endures. Bit (0x36)
cal_rdy is ´0´ when (0x36) cal_trigger is not ´00´.
Fast compensation should not be used in combination with low-power mode. In low-power
mode the conditions (availability of necessary data) for proper function of fast compensation are
not fulfilled.
4.6.3 Manual compensation
As explained above, the contents of the public compensation registers (0x38, 0x39, 0x3A)
offset_filt_x/y/z and (0x3B, 0x3C, 0x3D) offset_unfilt_x/y/z can be set manually via the digital
interface. It is recommended to write into these registers immediately after a new data interrupt
in order not to disturb running offset computations.
Writing to the offset compensation registers is not allowed if slow compensation is enabled or if
the fast compensation procedure is running.
4.6.4 Inline calibration
For a given application, it is often desirable to calibrate the offset once and to store the
compensation values permanently. This can be achieved by using one of the aforementioned
offset compensation methods to determine the proper compensation values and then storing
Rev. 1.0
© 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.
Table 13: Fast compensation axis selection
cal_trigger
Page 21 / not for publishing
(0x36)
00b
01b
10b
11b
Data sheet
BMA250
Selected Axis
none
x
y
z
Bosch Sensortec
03 March 2011