Specifications

BMA180
Preliminary data sheet
Bosch Sensortec
Rev. 1.0 Page 30 / - proprietary information - 06 March 2009
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Specifications within this document are preliminary and subject to change without notice. Document is not intended for publication.
7.8 General functional settings
7.8.1 range
These 3 bits are used to select the full scale acceleration range (further included are the ADC-
resolutions)
range<2:0>
Full scale acceleration
range [+/- g]
ADC resolution
[mg/LSB]
000
10.13
001
1.5 0.19
010
20.25
011
30.38
100
40.50
101
80.99
110
16 1.98
111
Not authorised code Not authorised code
Directly after changing the full scale range it takes approximately 1/(2*bandwidth) before filters
(see next section) are providing correct data.
7.8.2 bw
A second order analogue filter defines the maximum bandwidth in the front-end-circuitry to 1.2
kHz. In order to further increase signal-to-noise-ratio, digital filters can be activated to reduce
the bandwidth down to 10 Hz. The digital filters are second order filters. Selection of the filters
could be done by using the 4 bits below (first 8 filters are low-pass filters).
bw<3:0> Selected bandwidth (Hz)
0000
10
0001
20
0010
40
0011
75
0100
150
0101
300
0110
600
0111
1200
1000
high-pass: 1 Hz
1001
band-pass: 0.2 Hz .. 300 Hz
1010 to 1111
not authorized codes
Interrupts should be disabled and re-enabled for each bw change (due to the risk of wrong
generated interrupt).
If bw value is written successively with 2 different values, a minimum delay of 10 µs between
the 2 write sequences must be respected to guarantee the latest value will be set correctly. This
is valid for image register. EEPROM access time is anyway much slower and this does not
affect ASIC function. bw setting is expected to be changed at very low rates.
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.