BMA020 Bosch Sensortec, BMA020 Datasheet - Page 48

• Manufacturer Part Number: BMA020
• Description: 3-AXIS ACCELEROMETER DIGITAL I/F
• Manufacturer: Bosch Sensortec

Specifications of BMA020

• Axis: X, Y, Z
• Acceleration Range: ± 2g, 4g, 8g
• Sensitivity: 256LSB/g, 128LSB/g, 64LSB/g
• Voltage - Supply: 2 V ~ 3.6 V
• Output Type: Digital
• Bandwidth: 3kHz
• Interface: I²C, SPI
• Mounting Type: Surface Mount
• Package / Case: 12-LGA
• For Use With: 828-1014 - BMA020 TRIBOX DEMO BOARD W/USB828-1008 - BMA020 DAUGHTERCARD FOR DEV KIT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 828-1000-2

Data sheet
BMA020
Bosch Sensortec
Digital, triaxial acceleration sensor
9. Internal logic functions
The sensor IC can inform the host system about specific conditions (e.g. new data ready flag or
acceleration thresholds passed) by setting an interrupt pin high even if interface communication
is not taking place. This feature can be used as “wake-up” indicator or “data ready flag” for
instance.
The interrupt performance can be programmed by means of control bits. Thus the criteria to
identify a special event can be tailored to a customer’s application and the sensor IC output can
be defined specifically.
9.1 High-g logic
For indicating high-g events an upper threshold can be programmed. This logic can also be
activated by a control bit. Threshold, duration and reset behaviour can be programmed.
See also section 3.2.8.
9.2 Any motion detection
The “any motion algorithm” can be used to detect changes of the acceleration. Thus it provides
a relative evaluation of the acceleration signals. The criterion is kind of a gradient threshold of
the acceleration over time. Thus one can distinguish between fast events with strong inertial
dynamic (e.g. shock), instant changes of force balance (e.g. drop, tumbling) and even slight
changes (e.g. touch of a mobile device).
Due to a high bandwidth and a fast response MEMS device the BMA020 is capable to detect
shock situations. The “any motion interrupt” or a high-g criterion setting can be used to give a
shock alert. The phase shift between onset of mechanical shock and interrupt output is defined
by the mechanical transfer function of the chassis and internal mounting interfaces (e.g. PDA
shell) and the data output rate of the sensor IC (currently 330µs, 100µs under consideration).
See also section 3.2.9.
9.3 Alert mode
Using the BMA020 it is possible to combine the “any motion criterion” with low-g and high-g
interrupt logic to improve the reaction time.
See also sections 3.2.9 and 3.4.2.
Rev. 1.2
Page 48
30 May 2008
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Note: Specifications within this document are subject to change without notice.