Electronic Design

Accelerometer Slashes Power Usage In Mobile Systems

The ADXL345 three-axis digital iMEMS (integrated microelectromechanical-system) accelerometer is the lowest-power device in its class, according to Analog Devices Inc. It uses 80% less power than other three-axis inertial sensors and incorporates an analog-to-digital converter that dramatically reduces power consumption in wireless handset, personal navigation devices, and other mobile applications.

The sensor’s FIFO memory block stores up to 32 sample sets of X, Y, and Z data, allowing the system to determine whether it should be actively responding to a change in movement or acceleration. Offloading that function from the host processor—the dominant power user in a typical system—permits it to remain in sleep mode as long as possible, reducing overall power usage by upward of 75% of the budget.

Unlike other devices, the ADXL345’s output data range scales from 0.1 Hz to 3.2 kHz. This allows designers to better manage energy consumption by precisely allocating power for a given system function and reserving unused power for other uses. The sensor also measures dynamic acceleration resulting from motion or shock, and its 10,000-g shock rating is well-suited for applications such as hard-disk drive protection in personal computers.

Other features include resolution of 4-mg per least-significant bit across all g ranges, single-tap and double-tap detection, activity and inactivity detection, freefall detection, and user-programmable threshold levels. The accelerometer includes I²C and three- and four-wire serial peripheral interface (SPI) digital interfaces and has a voltage range of 1.8 to 3.6 V.

The ADXL345 three-axis iMEMS digital accelerometer is available today in pre-production quantities with volume production scheduled for February 2009. The sensor comes in a small, thin 14-lead lead-frame chip-scale package (LFCSP) and costs $3.04 in 1000-unit quantities.

Analog Devices


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