BMA020 datasheet(44/50 Pages) BOSCH

44 / 50 page

Data sheet

BMA020

Digital, triaxial acceleration sensor

Bosch Sensortec

Rev. 1.2

Page 44

30 May 2008

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.

output can be generated and trigger the system master. The wake-up mode is used for ultra-low

power applications where inertial factors can be an indicator to change the activity mode of the

system.

The following table shows values calculated for the average current consumption during the

wake-up mode of the BMA020. The power consumption in wake-up mode is dependent on the

duration of the interrupt algorithm (number of data acquisitions) and the bandwidth (for more

details on setting of the bandwidth please refer to chapter 3.1.3).

Table 13: Average current consumption in self wake-up mode using high-g or low-g interrupt

Current consumption during BMA020 wake-up mode [µA]

(depending on bandwidth, calculated using typical values)

Pause [ms]

(@ 1,500Hz)

(@ 750Hz)

(@375Hz)

(@190Hz)

(@100Hz)

(@50Hz)

(@25Hz)

16.3

21,8

31.8

48.4

71.6

102.9

134.7

5.1

6.6

9.7

15.4

25.0

42.3

68.4

360

1.9

2.3

3.0

4.4

6.9

12.0

21.3

2,560

1.1

1.2

1.3

1.5

1.9

2.6

4.1

Durations of the pause values can vary for about ±30% due to the accuracy of the ultra-low-

power oscillator implemented within the sensor.

For estimating the typical current consumption in wake-up mode the following formula can be

applied:

i_self_wake_up = (i_DD · t_active + i_DDsbm · wake-up-pause) / (t_active + wake-up-pause)

With the approximation:

t_active = 1ms + 0.333ms · (4

⋅ 750 / bandwidth) + 0.333ms · (1500 / bandwidth) · n

With the following parameters:

i_DD

Current in normal mode

i_DDsm

Current in sleep mode

wake_up_pause

Setting of wake-up pause

number of data points in any-motion logic

(n=0 for high-g threshold and low-g threshold interrupt,

n=3 for any-motion logic)

Bandwidth

Setting of bandwidth (750-25 Hz),

for 1500Hz t_active = 1ms + 0.333ms · (1500/bandwidth) · n

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