BMA020 Bosch Sensortec, BMA020 Datasheet - Page 14

• 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

3.2.6 Latch_INT
If this bit (address 15h, bit 4) is at 1, interrupts are latched. The INT pad stays high until
microprocessor detects it and writes reset_INT control bit to 1 (section 3.3.1). When this bit is at
0, interrupts are set and reset directly by BMA020 according to programmable criteria (sections
3.2.7 and 3.2.8).
3.2.7 LG_thres, LG_hyst, LG_dur, counter_LG
LG_thres (address 0C, bits 7-0 / low-g threshold) and LG_hyst (address 11h, bits 2-0 / low-g
threshold hysteresis) can basically (although not recommended with BMA020) be used to detect
a free fall. The threshold and duration codes define one criterion for interrupt generation when
absolute value of acceleration is low for long enough duration.
Data format is unsigned integer.
LG_thres criterion_x is true if
LG_thres interrupt is set if
LG_thres criterion_x is false if
LG_thres interrupt is reset if
LG_thres and LG_hyst codes must be chosen to have (LG_thres + 32*LG_hyst) < 511.
When LG_thres criterion becomes active, an interrupt counter is incremented by 1 LSB/ms.
When the low-g interrupt counter value equals (LG_dur+1), an interrupt is generated.
Depending on counter_LG (address 0Bh, bit 3 and 2) register, the counter could also be reset
or count down when LG_thres criterion is false.
Table 6: Description of debouncing counter counter_LG
If latch_INT=0, the interrupt is not a latched interrupt and then it is reset as soon as LG_thres
criteria becomes false. When interrupt occurs, the interrupt counter is reset.
Remark: The LG_thres criteria is set with an AND condition on all three axes to be used for free
fall detection. However, please note due to the relatively wide sensitivity tolerance of the
BMA020 the absolute threshold values for low-g and high-g interrupt can only provide a rough
estimation of the motion profile.
Rev. 1.2
© Bosch Sensortec GmbH reserves all rights even in the event of industrial property rights. We reserve all rights of disposal such
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.
counter_LG<1:0>
00
01
10
11
low acceleration interrupt counter status when
Digital, triaxial acceleration sensor
LG_thres criteria is false
Count down by 1 LSB/ms
Count down by 2 LSB/ms
Count down by 3 LSB/ms
|acc_x |
(LG_thres criterion_x AND LG_thres criterion_y AND
LG_thres criterion_z) AND interrupt counter = (LG_dur+1)
|acc_x | > (LG_thres + 32*LG_hyst) / 255 * range
NOT(LG_thres criterion_x AND LG_thres criterion_y AND
LG_thres criterion_z)
reset
Data sheet
BMA020
Page 14
≤
LG_thres / 255 * range
Bosch Sensortec
30 May 2008