BMC150 datasheet(35/142 Pages) BOSCH

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Datasheet

eCompass BMC150

Page 35

BST-BMC150-DS000-04 | Revision 1.0 | July 2014

Bosch Sensortec

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. Not intended for publication.

4.5.1 Slow compensation

Slow compensation is based on a 1st order high-pass filter, which continuously drives the

average value of the output data stream of each axis to zero. The bandwidth of the high-pass

filter is configured with bit (0x37) cut_off according to .

Table 12: Compensation period settings

(0x37)

cut_off

high-pass filter

bandwidth

Example

bw = 500 Hz

*bw: please insert selected decimal data bandwidth value [Hz] from table 8

The slow compensation can be enabled (disabled) for each axis independently by setting the

bits (0x36) hp_x_en, hp_y_en, hp_z_en to ´1´ (´0´), respectively.

Slow 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 slow compensation

are not fulfilled.

4.5.2 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

approches the target value. This is best suited for “end-of-line trimming” with the customer’s

device positioned in a well-defined orientation. For fast compensation the g-range has to be

switched to 2g.

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. The public registers (0x38, 0x39, 0x3A) offset_filt_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:

Table 13: Fast compensation axis selection

(0x36) cal_trigger

Selected Axis

00b

none

01b

10b

11b

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