PORTLAND, Ore.— Claiming to shrink the size, increase the reliability and lower the cost of satellite airbag sensors, Freescale Semiconductor unveiled smart Xtrinsic airbag accelerometers using the Distributed Systems Interface (DSI) 2.5 standard at the Convergence 2010 automotive tradeshow in Detroit.
Modern automobiles deploy a variety of airbags depending upon where the impact occurs, requiring that satellite sensors to be deployed around the vehicle to collect and integrate signals to determine whether to trigger front-, side- or other supplemental restraint system (SRS) airbags.
DSI was pioneered by Freescale, Denso and TRW to interconnect satellite pressure, acceleration, occupant and buckle sensors to the main airbag electronic control unit (ECU). Freescale already supports the Peripheral Sensor Interface 5 (PSI5) protocol used by General Motors, Ford and many European car makers with its MMA51xxW and MMA52xxW satellite accelerometers. But the new MMA16xxW and MMA26xxW airbag sensors use DSI to bring its next-generation Xtrinsic airbag triggers to Chrysler and the many Japanese car makers using DSI.
Freescale's new Xtrinsic airbag sensors use the company's high aspect ratio micro-electromechanical system (HARMEMS) to provide a larger mass for the moveable element of the sensor, providing an overdamped transducer that is immune to the high-frequency vibrations that can trigger resonances within an accelerometer package, causing premature deployment.
High aspect ratio micro-electro-mechanical systems (HARMEMS) uses larger movable elements to provide overdamped transducers that are immune to high-frequency resonance.
"By using an overdamped transducer and marrying that to a QFN [quad flat no-lead package], which also changes the resonant frequency of the package almost 10X higher, we have eliminated the high-frequency signals altogether, which is key to maintaining a high level of integrity to air-bag deployment," said Jim Grothe, MEMS automotive solutions marketing manager at Freescale.
The MMA16xxW and MMA26xxW sensors are X- and Z-axis inertial satellite sensors, respectively, giving automobile manufactures flexibility in mounting orientation. A variety of g-force ranges and filter settings allow car makers to match up to four Xtrinsic airbag to vehicles on a single DSI bus at a 16 microsecond sample rate.
The smart Xtrinsic sensors include a self-test procedure performed at startup, or on-demand, to allow the vehicle's ECU to verify that the MMA16xxW and MMA26xxW airbag triggers are armed and ready.