Specifications

BMA180

Preliminary data sheet

Bosch Sensortec

Rev. 1.0 Page 18 / - proprietary information - 06 March 2009

as copying and passing on to third parties. BOSCH and the symbol are registered trademarks of Robert Bosch GmbH, Germany.

Specifications within this document are preliminary and subject to change without notice. Document is not intended for publication.

4.3 Wake-up mode

4.3.1 General information

In general BMA180 is attributed to low power applications and can contribute to the system

power management.

- Current consumption 575µA operational (low power mode)

- Current consumption < 1µA in sleep mode

- Wake-up time < 2ms and

- Start-up time < 3.5ms

- New data ready indicator to reduce unnecessary interface communication

- Sample skipping in combination with new data interrupt to reduce interface traffic

- Wake-up mode to trigger a system wake-up (interrupt output to master) in case of motion

- Low current consumption in wake-up mode

The BMA180 provides the possibility to wake up a system master when specific acceleration

values are detected. Therefore the BMA180 stays in an ultra low power mode and periodically

evaluates the acceleration data. If acceleration is above a certain threshold (e. g. high-g

threshold) an interrupt output can be generated, which triggers 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.

4.3.2 Current consumption in wake-up mode

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_DDsm · wake-up-pause) / (t_active + wake-up-pause)

With the approximation:

t_active = 2ms + 0.417ms · (2400 / bandwidth) + 0.417ms · (1200 / 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

n 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: 10 . . . 1200Hz

Thus, the relevant parameters for power consumption in self-wake up mode are:

- current consumption in normal mode

- current consumption in sleep mode

- self-wake up pause duration

- bandwidth (e. g. length of digital filter to be filled for one data point)

- interrupt criteria (determines the duration of normal operation)