BMA250 Bosch Sensortec, BMA250 Datasheet - Page 34

• Manufacturer Part Number: BMA250
• Description: 3-AXIS ACCELEROMETER DIGITAL I/F
• Manufacturer: Bosch Sensortec
• Series: -r

Specifications of BMA250

• Featured Product: BMA250 - Digital, Triaxial Acceleration Sensor
• Axis: X, Y, Z
• Acceleration Range: ±2g, 4g, 8g, 16g
• Sensitivity: 256LSB/g, 128LSB/g, 64LSB/g, 16LSB/g
• Voltage - Supply: 1.62 V ~ 3.6 V
• Output Type: I²C™, SPI™
• Bandwidth: 8Hz ~ 1kHz
• Interface: I²C, SPI
• Mounting Type: Surface Mount
• Package / Case: 12-VQFN
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• For Use With: 828-1024 - BMA250 DAUGHTERCARD FOR DEV KIT
• Other names: 828-1023-2

BMA250
Bosch Sensortec
Data sheet
4.8.9 Low-g interrupt
This interrupt is based on the comparison of acceleration data against a low-g threshold, which
is most useful for free-fall detection.
The interrupt is enabled (disabled) by writing ´1´ (´0´) to the (0x17) low_en bit. There are two
modes available, ‘single’ mode and ‘sum’ mode. In ‘single’ mode, the acceleration of each axis
is compared with the threshold; in ‘sum’ mode, the sum of absolute values of all accelerations
|acc_x| + |acc_y| + |acc_z| is compared with the threshold. The mode is selected by the
contents of the (0x24) low_mode bit: ´0´ means ‘single’ mode, ´1´ means ‘sum’ mode.
The low-g threshold is set through the (0x23) low_th register. 1 LSB of (0x23) low_th always
corresponds to an acceleration of 7.81 mg (i.e. increment is independent from g-range setting).
A hysteresis can be selected by setting the (0x24) low_hy bits. 1 LSB of (0x24) low_hy always
corresponds to an acceleration difference of 125 mg in any g-range (as well, increment is
independent from g-range setting).
The low-g interrupt is generated if the absolute values of the acceleration of all axes (´and´
relation, in case of single mode) or their sum (in case of sum mode) are lower than the threshold
for at least the time defined by the (0x22) low_dur register. The interrupt is reset if the absolute
value of the acceleration of at least one axis (´or´ relation, in case of single mode) or the sum of
absolute values (in case of sum mode) is higher than the threshold plus the hysteresis for at
least one data acquisition. In bit (0x09) low_int the interrupt status is stored.
The relation between the content of (0x22) low_dur and the actual delay of the interrupt
generation is: delay [ms] = [(0x22) low_dur + 1] • 2 ms. Therefore, possible delay times range
from 2 ms to 512 ms.
4.8.10 High-g interrupt
This interrupt is based on the comparison of acceleration data against a high-g threshold for the
detection of shock or other high-acceleration events.
The high-g interrupt is enabled (disabled) per axis by writing ´1´ (´0´) to bits (0x17) high_en_x,
(0x17) high_en_y, and (0x17) high_en_z, respectively. The high-g threshold is set through the
(0x26) high_th register. The meaning of an LSB of (0x26) high_th depends on the selected g-
range: it corresponds to 7.81 mg in 2g-range, 15.63 mg in 4g-range, 31.25 mg in 8g-range, and
62.5 mg in 16g-range (i.e. increment depends from g-range setting).
A hysteresis can be selected by setting the (0x24) high_hy bits. Analogously to (0x26) high_th,
the meaning of an LSB of (0x24) high_hy is g-range dependent: it corresponds to an
acceleration difference of 125 mg in 2g-range, 250 mg in 4g-range, 500 mg in 8g-range, and
1000mg in 16g-range (as well, increment depends from g-range setting).
The high-g interrupt is generated if the absolute value of the acceleration of at least one of the
enabled axes (´or´ relation) is higher than the threshold for at least the time defined by the
(0x25) high_dur register. The interrupt is reset if the absolute value of the acceleration of all
enabled axes (´and´ relation) is lower than the threshold minus the hysteresis for at least the
Rev. 1.0
Page 34 / not for publishing
03 March 2011
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Note: Specifications within this document are subject to change without notice.