Designed for applications that require battery lifetimes stretching out for many years, the Analog Devices ADXL362 three-axis microelectromechanical systems (MEMS) digital accelerometer has slashed power down to the industry’s lowest levels. It consumes a measly 300 nA in its motion-sensing wakeup mode, which is 60% lower than available competitive accelerometers. In full measurement mode, it needs just 2 µA at a 100-Hz data rate, which is 80% less than the competition. It features the industry’s lowest sleep mode current dissipation at 10 nA as well.
The ADXL362 provides acceleration data with 12-bit resolution, as well as 8-bit formatted data for more efficient single-byte transfers when a lower resolution is sufficient. It features measurement ranges of ±2, ±4, and ±8 g with a resolution of 1 mg/LSB in the ±2-g range. And, it does all this in a 3- by 3.25- by 1.8-mm, 16-pin land-grid array (LGA) package (Fig. 1).
“This accelerometer will run for over 75 years on a coin cell battery, provided the battery lasts that long, while continuously sensing motion in the wakeup mode,” says Bill Murphy, product line director for the MEMS and Sensors Group at Analog Devices. This kind of low-level power dissipation suits many areas in agricultural, transportation, medical, remote, dangerous environment, infrastructure monitoring, and Smart Grid metering applications.
Unlike other MEMS accelerometers that use power duty cycling to achieve low power consumption, the ADXL362 does not alias input signals by under-sampling. It samples the sensor’s full bandwidth at all output data rates that are user-selectable in eight steps.
System-Level Power Savings
Additional features enable system-level power efficiency. The ADXL362 can be used as part of an intelligent, continuously operational motion-activated switch. Equipped with an awake status output pin, the accelerometer can instantly trigger a switch that turns on system functions, bypassing the processor, to further reduce system power.
“Designing for low power requires more than low current draw at the component level. It also means intelligently managing total system power by turning system functions on and off at precisely the correct time,” notes Murphy. “This enables applications ranging from healthcare to infrastructure monitoring, where battery life is absolutely critical.”
The accelerometer’s integrated enhanced sample activity detection function accurately distinguishes between different kinds of motion. This eliminates false positives and prevents the sensor from turning the system on unnecessarily and costing additional battery life. An embedded deep internal first in, first out (FIFO) memory block allows system designers to record data and stream long data sets, reducing the processor load and saving additional system power. The accelerometer features a 12-bit an analog-to-digital converter (ADC) and a serial-to-parallel interface (SPI) port as well (Fig. 2).
Two lower-noise modes are available to roughly halve the noise at the expense of a few microamps. There’s also a built-in micro-power temperature sensor. And, the ADXL326 can synchronize the sampling time to an external trigger.
The ADXL326 is designed for use in applications that require many sensors and batteries that need to be replaced. For example, it will be used in the second-generation Blast Gauge made by BlackBox Biometrics and developed by the U.S. Defense Advanced Research Projects Agency (DARPA). The Blast Gauge has proven reliable for detecting brain concussive forces faced by Armed Forces personnel in war zones.
The accelerometer also can be used to monitor and track herds of cows and other farm animals, using collars that include the accelerometer and its circuitry. It can be used for motion and activity detection in Smart Grid meters, transportation vehicles like semis, and underwater and overwater gas, water, and fuel pipelines as well. Samples of the ADXL362 are available now with production quantities available this August at $3.97 each.