Electronic Design

13-Bit MEMS Motion Sensor Fits Into Tight Designs

The iMEMS ADXL346 digital three-axis smart motion sensor from Analog Devices features resolution up to 13 bits and an embedded FIFO that enables significant power savings by managing host processor power, according to the company. Measuring 3 by 3 by 0.95 mm, it’s designed to measure tilt, shock, and acceleration in space-constrained portable devices. It operates at a primary supply voltage down to 1.8 V and offers 4-mg/LSB resolution, which enables, for example, the measurement of inclination changes of as little as 0.25°.

The sensor’s three-axis “smart” motion measurement system features selectable measurement ranges. The device measures both dynamic acceleration resulting from motion or shock and static acceleration, such as gravity, which allows it to be used as a tilt sensor. It also automatically modulates its power consumption in proportion to its output data rate and saves additional power by automatically switching to a sleep mode during periods of inactivity. A standby mode provides even further power savings.

The ADXL346’s on-chip FIFO memory block stores up to 32 sample sets of X-, Y-, and Z-axis data, effectively offloading the FIFO function from the host processor. This allows the host processor and other power-hungry peripherals to go into a sleep mode until needed, saving significant system power, according to Analog Devices. The company also says that effective use of this feature can dramatically decrease overall power usage by up to 75%.

Furthermore, the ADXL346 has a wide, selectable bandwidth of 0.1 to 1600 Hz, unlike competing 1.8-V capable accelerometers, which have a maximum bandwidth of 100 Hz, Analog Devices says. Power consumption ranges from less than 150 µA at 1600 Hz down to 25 µA under 10 Hz. The ADXL346 also measures dynamic acceleration with ±2/4/8/16-g user-selectable measurement ranges resulting from motion or shock. And, it includes built-in orientation sensing via simple register reads.

Several special sensing functions are programmed on-chip along with user-programmable threshold levels. Activity and inactivity sensing detect the presence of or lack of motion or if the acceleration on any axis exceeds a user-set level. A tap sensing function detects single and double taps. Freefall sensing detects if the device is falling. These functions can be mapped to one of two interrupt output pins. In addition, the accelerometer includes I²C and three- and four-wire serial peripheral interface (SPI) digital interfaces.

The ADXL346 digital three-axis iMEMS accelerometer is available now in sample quantities with volume production scheduled for August 2009. It comes in a 16-lead land-grid array (LGA) package and costs $3.04 per unit in 1000-unit quantities.

Analog Devices


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