Accelerometer Applications Expand

Highly integrated and compact accelerometers have enabled key functions in several portable products. These dual and three-axis units can provide tilt detection, low-level vibration monitoring and higher level monitoring for shock readings. However, each of these applications requires a different accelerometer to address the appropriate g-level measurements. Freescale Semiconductor's MMA7260Q three-axis accelerometer allows the selection of four g-levels from 1.5 to 6g, so a single accelerometer can address several applications.

Using microelectromechanical system or MEMS technology, the MMA7260Q has X and Y-axes accelerometers formed by a comb structure in one plane and a Z-axis measurement created by a movable plate. These movable elements and a separate signal conditioning circuitry mount in a 16-lead QFN plastic package. Part of the accelerometer circuitry includes two logic inputs that allow the selection of plus or minus 1.5, plus or minus 2, plus or minus 4, or plus or minus 6g. An additional gain stage changes the sensitivity from a maximum of 800 to a minimum 200 mV/g (typical) but the tolerance is plus or minus 7.5 percent for each range. The programmable aspect allows a microcontroller (MCU) to select the appropriate sensitivity based on the application. As a result, the sensitivity can be changed anytime during the operation of the product. For example, if a measurement on a lower range exceeds the maximum limit for 2 msec, the MCU can automatically adjust the g-range to a higher level and sample the data again.

With MCU selected sensitivity, the accelerometer can switch from a tilt detection or freefall algorithm with a 1.5g setting to a vibration algorithm with the 6g setting. The different sensitivities provide optimized performance in low g applications.

CONTACT: Freescale Semiconductor's Technical Information CenterTel: 1-800-521-6274