Electronic Design

Mini Low-g Accelerometers Sport Five Functions

Featuring an acceleration range of 1.5 to 10 g, a family of capacitive MEMS sensors offers tilt, motion, position, shock, and vibration sensing to satisfy a host of low-cost applications.

Consumer, computer, automotive, industrial, medical, and scientific applications are all potential fits for a broad range of low-cost and low-g dual-axis MEMS sensors introduced by Freescale Semiconductor, a wholly owned subsidiary of Motorola Inc. The MMA62xxQ family of dual-axis, capacitive, MEMS-based sensors covers the acceleration range of 1.5 to 10 g (within ±1.5 g). They come in tiny 16-pin quad flat no-lead (QFN) packages measuring only 6 by 6 by 1.98 mm. That's 73% smaller in footprint than the typical SOIC-20 packages that house other acceleration sensors (Fig. 1).

The chips contain signal-conditioning circuitry, a single-pole low-pass filter, and temperature-compensation circuitry. Zero-g offset for the full-scale span and the filter's cutoff frequency are factory-set and require no external devices. A full system self-test capability is also included on-chip. "We're aiming to be the pre-eminent supplier of silicon solutions for sensing real-time change in transportation and standard products," says Bob Johnson, Freescale's market development manager.

The company is making the sensor family available in units that sense tilt, motion, position, shock, and vibration in two directions (X and Y axes). "Putting all of these functional capabilities into one chip saves pc-board space and reduces heat dissipation and cost," adds Johnson.

The sensors range in operating frequency between 50 and 900 Hz, allowing designers to select the appropriate devices for their requirements. The sensors operate from 2.7 to 3.6 V and dissipate maximum current of 1.5 to 3 mA, depending on the model chosen. Noise ratings range from 1.3 to 3.5 mVRMS (over 0.1 Hz to 1 kHz), again depending on the sensor model.

Six models will be available. The MMA6260Q, 6261Q, 6262Q, and 6263Q feature 800-mV/g sensitivity at 50, 300, 150, and 900 Hz, respectively. The 6231Q and 6233Q offer 120-mV/g sensitivity at 300 and 900 Hz, respectively. These sensors suit consumer, scientific, computer, industrial, medical, and automotive applications (Fig. 2).

Also available, Freescale's RD1986MMA6260Q TRIAX evaluation board includes two low-g accelerometers, the MC6908KX8 MCU, a serial communications port, EEPROM, and a piezo-horn. The board displays a three-axis solution with two accelerometers in the QFN package.

In 1000-unit quantities, each sensor costs $3.60. Higher quantities run for less. The D1986MMA6260Q reference design goes for $49.

Freescale Semiconductor Inc.
www.freescale.com

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