Every new feature introduced to a portable device, handheld instrument, and other battery-operated medical and industrial electronic devices taxes already stressed power budgets. To address the growing demand for more motion-enabled features, Analog Devices, Inc. (ADI) has developed a new family of smart motion sensors specifically for power- and space-constrained portable devices. The ADXL346 digital three-axis iMEMS® smart motion sensor is ADI's latest offering in this new class of small, ultra lower-power, high-resolution iMEMS® accelerometers for measuring tilt, shock, and acceleration. Designed to operate at a primary supply voltage down to 1.8-V, these new motion sensors, first introduced at the Consumer Electronics Show in January, are capable of high resolution (4 mg/LSB) which enables, for example, measurement of inclination changes as little as 0.25 degrees.
Within the ADXL346’s small 3mm x 3mm x 0.95mm footprint, is a complete three-axis “smart” motion measurement system with selectable measurement ranges. The ADXL346 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. The device automatically modulates its power consumption in proportion to its output data rate as well as saves additional power by automatically switching to a sleep mode during periods of inactivity. For even more power savings, a standby mode can also be used.
“Motion sensing has moved beyond the initial concept of just acceleration and now includes tilt, shock, vibration, and rotation,” said Bill Murphy, product line director for Micromachined Products, Analog Devices. “The cost effective measurement of these forces while consuming very little of the power budget has enabled a new wave of innovative product features and capabilities.”
The ADXL346 features an on-chip FIFO (first-in/first-out) memory block that stores up to 32 sample sets of X-, Y-, and Z-axis data and effectively off-loads 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. Effective use of this feature can dramatically decrease overall power usage by up to 75 percent.
More About the ADXL346
The ultra-low-power ADXL346 digital accelerometer has wide, selectable bandwidth of 0.1 Hz to 1600 Hz, unlike competing 1.8 V capable accelerometers which have a maximum bandwidth of 100 Hz. This allows portable system designers to build very responsive, real time embedded systems that provide the user experience that’s in demand. Power consumption ranges from less than 150 uA at 1600 Hz bandwidth down to 25 uA under 10 Hz. The ADXL346 also measures dynamic acceleration with ±2g/4g/8g/16g user-selectable measurement ranges resulting from motion or shock and also includes built in orientation sensing via simple register reads.
Several special sensing functions are also 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. Free-fall sensing detects if the device is falling. These functions can be mapped to one of two interrupt output pins. In addition, the new accelerometer includes I²C and three- and four-wire SPI (serial peripheral interface) digital interfaces.