GENERAL DESCRIPTION

The BMA421 is an ultra-small, triaxial, low-g acceleration sensor

with digital interfaces, aiming for low-power consumer

electronics applications. Featuring 12 bit digital resolution and

embedded intelligence, the BMA421 allows low-noise

measurement of accelerations in 3 perpendicular axes and thus

senses any-motion/no-motion and enables plug ’n’ play step

counting in smart phones and wearable devices. Furthermore

the device is optimized to fulfill low power step counter

requirements.

SENSOR FEATURES

With its embedded intelligence BMA421 is unique in the class of

consumer grade accelerometers for smart phones, wearable

devices and toys and gadgets. The embedded intelligence

enables precise low current always on step-counting at 25 µA in

smartphones and wearable devices (e.g. wrist bands). Featuring

a high performance measurement mode with low pass filters and

a current consumption of only 150 μA the BMA421 is robust to

vibrations and aliasing. In low-power mode operation the current

consumption can be even further reduced by more than one

order of magnitude. This fulfills the current consumption

requirements for always-on applications and wearable devices.

The BMA421 is highly configurable in order to give the designer

full flexibility when integrating the sensor into the system.

TECHNICAL SPECIFICATIONS

BMA421 Technical data

Digital resolution

12 bit

Resolution

(in ±2g range)

0.98 mg

Measurement ranges

(programmable)

±2 g; ±4 g; ±8 g; ±16 g

Sensitivity

(calibrated)

±2 g: 1024 LSB/g

±4 g: 512LSB/g

±8 g: 256 LSB/g

±16 g: 128 LSB/g

Zero-g offset

(typ., over life-time)

±100 mg

Noise density (typ.)

300 µg/√Hz

Output data rate

(programmable)

1600 Hz … 8 Hz

Digital inputs/outputs

2x digital interrupt pins

1.62 … 3.6 V

I/0 supply voltage

1.2 … 3.6 V

Temperature range

-40 … +85 °C

Current consumption

– full operation

– low-power mode

150 µA

13 µA (@ 50 Hz data rate)

FIFO data buffer

1 kB

LGA package

Shock resistance

10,000 g x 200 µs

SENSOR OPERATION

The BMA421 supports two modes of operation:

1) Standard data polling mode: Acceleration data is directly read-

out via the sensor’s digital interface and computed by a system

μController, application processor or a baseband processor. An

integrated FIFO with 1 kB of size can be used optionally to

reduce overall system current consumption.

Bosch Sensortec

BMA421

Intelligent, triaxial acceleration sensor

BMA421 TARGET APPLICATIONS

 Step-counting in smartphones

 Step-counting in wearable devices

 Low power user interaction

 Gesture recognition

 Advanced power management for mobile devices

 Tilt compensation for electronic compass