Freescale inertial sensors enhance sensitivity of safety-critical automotive airbag systems

HARMEMS technology designed to dampen sensor resonant frequency for more reliable and accurate airbag activation

Freescale Semiconductor has introduced a family of inertial sensors designed to enhance the performance, sensitivity and reliability of next-generation automotive airbag systems. Freescale’s new medium- and high-acceleration (medium-g and high-g) accelerometers are engineered to detect a crash by measuring the abrupt deceleration of a vehicle and then triggering airbag deployment.

Freescale’s MMA6222EG, MMA6255EG and MMA621010EG inertial sensors are based on next-generation high aspect ratio micro-electromechanical systems (HARMEMS) technology, a proven technology for airbag sensing applications. The accelerometers’ advanced transducer design enhances sensor offset performance and over-damping response, which helps improve system reliability and resistance to high-frequency and high-amplitude parasitic vibrations. The devices are designed to help distinguish airbag system conditions that might trigger a false deployment, such as a door slam or high vibrations during vehicle assembly.

The MMA62xxEG inertial sensors accommodate 3.3V and 5V supply voltage and offer developers the flexibility to use digital or analog outputs. The sensors also support bi-directional self-test and feature a serial peripheral interface (SPI) bus for enhanced monitoring capabilities.

Strong demand for airbag sensors
Demand for airbag-related systems is driven by a combination of legislation, consumer influences and automotive growth in emerging markets.

“Safety system sensors follow powertrain as the second largest sensor category in terms of market value, and safety sensor growth remains strong," said Mark Fitzgerald, an analyst at Strategy Analytics. "Sensing for airbag systems is the largest application for automotive safety sensors in both unit volume and market value, and suppliers that offer competitively priced, reliable and high-performance inertial sensor solutions are well positioned in this market."

Airbag distributed sensing systems can include two main ECU inertial sensors and up to seven satellite sensor modules around the car perimeter for front and side impacts. Freescale’s MMA62xxEG inertial sensors typically are included in the main ECU of the airbag application. A leading supplier of automotive MEMS sensors for the main ECU and satellite sensor modules, Freescale offers a wide range of standard sensing devices, such as MMA62xxEG sensors, as well as custom sensing solutions.

"As a leading automotive MEMS sensor supplier for more than 10 years, our design methodology integrates hardware and software by optimizing the partitioning between Freescale technology and our customers’ intellectual property blocks for high-performance sensing solutions,” said Demetre Kondylis, vice president and general manager of Freescale’s Sensor & Actuator Solutions Division. "Freescale’s standard and customer-specific inertial sensors offer exceptional integration and system scalability as developers continue to cluster safety systems, while maintaining a commitment to zero-defect quality.”

In addition to supporting automotive airbag applications, Freescale’s MMA6222EG sensor is an ideal choice for applications that require measurement of small forces (±20 g) resulting from vibration or shock. Examples include:

Preventative maintenance systems for industrial equipment in which an accelerometer monitors the frequency, amplitude and spectrum of the vibration signature to help enable proactive machine health
Shock detection systems that assess a package’s treatment during the shipping and handling process.

About HARMEMS technology
Freescale’s next-generation HARMEMS technology provides over-damped mechanical response and exceptional signal-to-noise ratio to address a wide range of automotive safety applications, from airbag systems to electronic stability control (ESC). Over-damped HARMEMS technology enables a high degree of immunity to high-frequency, high-amplitude parasitic vibrations found in vehicle cabins and engine compartments. For airbag applications, the higher signal-to-noise ratio combined with Freescale’s DSP-based signal chain provides a wide range and high sensitivity with less than one least significant bit (LSB) noise.

MMA62xxEG product features

XY-axis of sensitivity in one device
10-bit digital data output
±20 g, ±50 g or ±100 g full-scale range per axis
MMA6222EG: ±20 g (±4 percent sensitivity accuracy at 25 degrees C)
MMA6255EG: ±50 g (±4 percent sensitivity accuracy at 25 degrees C)
MMA621010EG: ±100 g (±4 percent sensitivity accuracy at 25 degrees C)
Full-scale range is specified independently for each axis
Selection of integrated signal conditioning low-pass filters
First order IIR high-pass filter option
SPI-compatible serial interface
Bi-directional internal self-test
On-chip temperature sensor and voltage regulator
Support for signed or unsigned output data
Capture/hold input for system-wide synchronization support
3.3 V or 5 V single supply operation
Ratiometric analog voltage output
Minimal external component requirements
Wide operating temperature range from -40 degrees C to +105 degrees C
Robust 20-pin SOIC wide-body RoHS-compliant package

Pricing and availability
The following MMA62xxEG inertial sensors are available now:

MMA6222AEG analog output trimmed, ±20 g
MMA6222EG digital output trimmed, ±20 g
MMA6255AEG analog output trimmed, ±50 g
MMA6255EG digital output trimmed, ±50 g
MMA621010AEG analog output trimmed, ±100 g
MMA621010EG digital output trimmed, ±100 g

Suggested resale pricing for the MMA62xxEG sensors in 10,000-piece quantities starts at $7.75 (USD).

For more information about Freescale’s sensor portfolio, visit www.freescale.com/files/pr/sensors.html.

From: http://freescale.com

Publication date: 12.11.2008

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