Specifications

BMA180
Preliminary data sheet
Bosch Sensortec
Rev. 1.0 Page 21 / - 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.
ZYXT
ZYXT
INT
330µs at bw=1.5kHz
ZYXT
ZYXT
INT
ZYXT
ZYXT
INT
330µs at bw=1.5kHz
5 Data conversion
5.1 Acceleration data
Acceleration data are converted by a 14bit ADC. The description of the digital signal is "2’s
complement". The 14bit data are available as LSB (at lower register address) and MSB. It is
possible to read out MSB only (8bit) or LSB and MSB together (16bits with 14 data bits and 1
data ready bit). In second case LSB- and MSB-data are closely linked to avoid unintentional
LSB/MSB mixing when read out and data conversion overlap accidentally (7.13.2).
The acceleration data is filtered by a second order analogue filter at 1.2kHz. Additionally, all
data can be processed by digital filtering (2-pole filter) to reduce noise level (10Hz . . . 600Hz)
and to filter out undesired frequencies. The transfer function of the mechanical element is
designed to avoid resonance effects at frequencies below the bandwidth of the ASIC.
The availability of new data can be checked in two ways:
• Bit 0 from the LSB data registers is an indicator whether data has already been read out
or the data is new (new-data bits, see 7.13.2)
• The interrupt pin can be configured to indicate new data availability. The synchronization
of data acquisition and data read out enables the customer to avoid unnecessary
interface traffic in order to reduce the system power consumption and the crosstalk
between interface communication and data conversion.
Figure 4: Explanation of data ready interrupt: For a bandwidth of e.g. 1.2kHz the data refresh
cycle takes 417µs to update all data registers. After the final conversion of z-axis the INT pad
will be set high. New data can be read out via interface (recommendation: read out within 20µs
after interrupt is high during the conversion of the next temperature value). The interrupt resets
automatically after read out.
5.2 Temperature measurement
Temperature data are converted to an 8bit data register. The temperature output range can be
adapted to customer’s requirements by offset correction.
417 µs for bw = 1200 Hz