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Dual-axis accelerometers improve ESC systems

Posted: 15 Sep 2008 ?? ?Print Version ?Bookmark and Share

Keywords:low-g accelerometer? ESC system? SNR?

Freescale Semiconductor has unveiled its low-gravity (low-g) MMA6700/1EG accelerometers at last week's (Sept. 10) Freescale Technology Forum Japan. The dual-axis inertial sensors for electronic stability control (ESC) systems are claimed to deliver more intelligence to automotive safety systems.

Key specs for the MMA6700 series include XY-axis of sensitivity in one device, 10- or 11bit digital data output, and 3.5g or 5g full-scale range per axis. The series consists of the 3.5g MMA6700EG (11bit data sensitivity = 3.43mg/digit typical at 25C) and the 5 g MMA6701EG (11bit data sensitivity = 4.91mg/digit typical at 25C).

Leveraging Freescale's high aspect ratio micro-electromechanical systems (HARMEMS) technology, which are said to feature an advanced transducer design that delivers an overdamped mechanical response and a better SNR, the MMA6700 devices are said to deliver a much wider dynamic range and better sensitivity. Since the ESC system is installed either in the vehicle cabin or under the hood, overdamped HARMEMS technology enables a high degree of immunity to high-frequency, high-amplitude parasitic vibrations, said Freescale.

This means with the MMA6700/1EG accelerometers' wide dynamic range, it enables ESC designers to filter out extraneous signals such as parasitic vibrations that could potentially interfere with the vehicle's lateral acceleration measurement, Freescale said. In addition, the accelerometers' integrated DSP provides higher accuracy and improves signal integrity for ESC applications.

For ESC applications, the higher SNR combined with Freescale's DSP-based signal chain is designed to provide both a wide range and high sensitivity with less than one least significant bit (LSB) noise, Freescale said.

Operating from a 3.3V or 5V single supply, the MMA6700 devices provide a selection of integrated signal conditioning low-pass filters, support for signed or unsigned output data, and five customer-assigned, one-time-programmable (OTP) bytes. Other features include a SPI-compatible serial interface, a ratiometric analog voltage output and capture/hold input for system-wide synchronization support. It also supplies a bidirectional internal self-test and an on-chip temperature sensor and voltage regulator. The operating temperature range is -40C to 125C.

The low-g accelerometers, housed in a 20-pin SOIC wide-body RoHS-compliant package, can also be used in a variety of embedded applications that require measurement of small forces such as those resulting from shock, vibration, tilt, movement or acceleration. Applications include washing machines, sports medicine equipment, video game pads, seismic detectors and security systems.

The suggested resale price starts at $7.67 for the MMA6700EG and the MMA6701EG in quantities of 10,000. Samples of the MMA6700/1EG devices are available now to automotive customers. Volume production will begin in April 2009.

- Gina Roos

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