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 ±1.5, ±2, ±4, or ±6g. An additional gain stage changes the sensitivity from a maximum of 800 to a minimum 200 mV/g (typical) but the tolerance is ±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
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g-Select
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g-Select1
|
g-Range
|
sensitivity
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| 0 |
0 |
1.5g |
800 mV/g |
| 0 |
1 |
2g |
600 mV/g |
| 1 |
0 |
4g |
300 mV/g |
| 1 |
1 |
6g |
200 mV/g |
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