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Sensor touts industry-first g-selectable capability

Posted: 13 May 2005 ?? ?Print Version ?Bookmark and Share

Keywords:freescale semiconductor? microelectromechanical systems sensor? mems sensor? sensor? mma7260q?

Freescale Semiconductor claims to have developed the industry's first three-axis, low-gravity (low-g), microelectromechanical systems (MEMS) sensor with a g-select feature. Designed for the portable consumer electronics market, the new MMA7260Q accelerometer also touts a fast response time, low current consumption, low supply voltage and high sensitivity, all in a small package size.

A key benefit of the new MMA7260Q accelerometer is its g-select feature that ranges from 1.5g to 6g. The sensitivity can be selected for 1.5g (freefall, tilt compensation), 2g (handheld motion detection for game controllers), 4g (low vibration monitoring such as for shipping and handling) or 6g (high vibration monitoring). This gives designers the flexibility to select the g-force detection level for specific application needs. In addition, it also reduces component count, which helps improve heat dissipation and overall production costs, said the company.

The g-selectable feature allows the designer to select different g ranges on-the-fly. You're not doing a hardware or device change; it's using a microcontroller in conjunction with the accelerometer, and it can be changed for many different applications," said Michelle Clifford, applications engineer for Freescale's Sensors and Analog Product Division.

The new accelerometer is a single-chip device that detects in three dimensions, XYZ, allowing portable devices to respond to changes in position, orientation and movement. The small package size of 6-by-6mm with a 1.45mm height requires less board space, and the quick turn-on time (1ms) and sleep mode (3?A) make the accelerometer suitable for battery-powered electronics such as PDAs, cellphones, 3D games and digital cameras.

The company notes that the competition's fastest response time is 1.6ms, with many others at >5 ms. The device also features a low current consumption of 500?A, a low voltage operation of 2.2V to 3.6V, and a high sensitivity of 800mV/g. In addition, it also exhibits low noise for higher resolution and higher accuracy.

"All of these thingslow current consumption of 500?A, sleep mode of 3?A, low voltage operation from 2.2V to 3.6V and fast turn-on timecombined together provide a low current draw for handheld electronics that doesn't use that much battery power," Clifford said.

Overall, the three-axes detection in a single package saves cost and PC-board space, and the g-selectable feature gives a designer the freedom to select different options for different applications, Clifford said, as well as reduces the number of part numbers in a BoM.

The new device measures small forces resulting from fall, tilt, motion, positioning, shock or vibration to provide protection for shock-sensitive components in many different applications. It detects acceleration or deceleration, such as when a device is dropped, helping prevent damage to the device and minimizing the risk of data loss, according to the company. For example, the new sensor has been designed into two of Samsung Electronics' digital audio players where the sensor is used for menu scroll by tilt and freefall detection

Shock is the measurement that accelerometers were originally designed for in airbag applications, but now with the additional five measurements, accelerometers can be used in many different products, Clifford said.

To evaluate the sensor, Freescale offers a sensing triple-axis reference design (STAR) and an evaluation board. The RD3112MMA7260Q board includes the three-axis MMA7260Q accelerometer, the MC68HC908KX8 microcontroller (MCU), a serial port connection, EEPROM and a piezo horn. Software is also included to show the six sensing functions in various graphical user interface (GUI) modules. The company offers software that can be downloaded from the web that gives engineers all the different options that accelerometers provide. A separate evaluation board (KIT3109MMA7260Q) is also available.

Packaged in a 16-lead QFN package, the suggested list price is $5.23 each in quantities of 10,000. Available now, the reference design (part number RD3112MMA7260Q) is priced at $57, and the 3-axis evaluation board (KIT3109MMA7260Q) is priced at $35.

- Gina Roos

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