BMA150 datasheet(12/56 Pages) BOSCH

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Data sheet

BMA150

Triaxial, digital acceleration sensor

Bosch Sensortec

Rev. 1.6

Page 12

30 October 2008

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.

3.1.3 Bandwidth

These three bits (address 14h, bits 2-0) are used to setup the digital filtering of ADC output data

to obtain the desired bandwidth. A second order analogue filter defines the max. bandwidth to

1.5kHz. Digital filters can be activated to reduce the bandwidth down to 25Hz in order to reduce

signal noise. The digital filters are moving average filters of various length with a refresh rate of

3kHz.

Since the bandwidth is reduced by a digital filter for the factor ½ , ¼, ... of the analogue filter

frequency of 1.5kHz the mean values of the bandwidth are slightly deviating from the rounded

nominal values. Table 4 shows the corresponding data:

Table 4: Settings of bandwidth

bandwidth<2:0>

Nominal selected bandwidth

[Hz]

Min.

Mean

bandwidth[Hz]

Max.

000

001

010

100

011

190

188

100

375

101

750

110

1500

111

Not authorised code

At wake-up from sleep mode to normal operation, the bandwidth is set to its maximum value

and then reduced to bandwidth setting as soon as enough ADC samples are available to fill the

whole digital filter.

Important note:

Please refer to the comment in chapter 3 of how to protect bits 5, 6 and 7 when modifying other

bits of register 14h.

3.1.4 Wake_up

This bit (address 15h, bit 0) makes BMA150 automatically switching from sleep mode to normal

mode after the delay defined by wake_up_pause (section 3.1.5). When the sensor IC goes from

sleep to normal mode, it starts acceleration acquisition and performs interrupt verification

(section 3.2). The sensor IC automatically switches back from normal to sleep mode again if no

fulfilment of programmed interrupt criteria has been detected. The IC wakes-up for a minimum

duration which depends on the number of required valid acceleration data to determine if an

interrupt should be generated.

If a latched interrupt is generated, this can be used to wake-up a microprocessor. The sensor IC

will wait for a reset_INT command and restart interrupt verification. BMA150 can not go back to

sleep mode if reset_INT is not issued after a latched interrupt.

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