ESC accelerometer complies with safety standards
By Margery Conner, Technical Editor -- EDN, September 15, 2008
ESC (electronic stability control) for automobiles is a well-established technology: In 2007, manufacturers sold more than 20 million ESC-equipped cars, accounting for approximately one-third of total autos sales. ESC’s role in making cars safer led the NHTSA (National Highway Traffic Safety Administration) to require ESC systems on all passenger cars, multipurpose vehicles, trucks, and buses that automakers sell in the United States starting in model year 2012. The technology relies on low-g-force, two-axis sensors to measure a vehicle’s lateral and longitudinal acceleration. When these sensors detect potentially unstable driving conditions, the system sends data to the car’s engine and braking system to maintain vehicle control.
Targeting ESC, Freescale’s new MMA6700/1EG MEMS (microelectromechanical-system) accelerometers combine a wide dynamic range with high resolution. The devices’ wide dynamic range enables the filtering of extraneous signals, such as parasitic vibrations, that could interfere with a vehicle’s lateral-acceleration measurement. An integrated DSP provides support for proprietary algorithms for improved signal integrity.
The low-g sensors in an ESC system require only about 1.7 to 2g of range. The MMA6700/1EG devices provide 11 bits of accuracy and a 3.5 to 5g range to prevent the detector’s electronics from saturating in extreme driving events. The sensor’s bidirectional internal self-test electrostatically moves the transducer in both directions to verify sensor accuracy during the initial ignition-on test. It operates from a 3.3 or a 5V single supply and has an operating-temperature range of −40 to +125°C. The chip comes in a 20-pin-SOIC, wide-body, ROHS (restriction-of-hazardous-substances)-compliant package and sells for $7.67 (10,000).
