Automotive airbag triggers incorporate a high degree of intelligence, as well as analog sensitivity and mixed-signal functionality. Today, smart airbags have occupant-detection features and inflate to variable volumes. Tomorrow's intelligent systems will also determine the firing sequence for multiple airbags. It is not surprising, then, that airbag triggers resemble complex systems-on-chip.
The airbag analyzed here, manufactured by Robert Bosch for the Ford Focus, is representative of the modules used in midrange vehicles. Apart from the microcontroller, the major semiconductor components are Bosch ASSPs.
The acceleration sensors on the board are microelectromechanical system devices that kick-start the triggering of the airbag. They use fixed and moving finger structures and spring pins. The sensing is fully electronic. Because of the low capacitance of the capacitive sensors, the signal-conditioning electronics (which include an amplifier and data converter) are placed in the same package with the sensor element.
(Click on image to enlarge)
The main microcontroller, which processes the sensor data and initiates the firing, is an ASIC from Texas Instruments' TMS470 family, derived from 16/32- bit ARM cores. An STMicroelectronics E2PROM stores information about the sequence of events leading to firing. The MCU-based safety controller prevents unwarranted airbag activation. The power-supply and voltage-regulator IC supplies power for the electrolytic capacitors that store electric charge used for igniting the airbag firing squibs.
The squib firing circuits ignite the pyrotechnics to inflate the airbags. Each squib is filled with sodium azide pellets that explode to fill the airbag with nitrogen when ignited by an electric spark. A two-stage airbag is fitted with two squibs, charged serially or in parallel.
This article was adapted from the Gartner Dataquest Research report "Dataquest Insight: Solid Prospects for Airbag Control Module Semiconductors, ID Number G00147010.
Mike Williams (firstname.lastname@example.org) is research vice president and Adriana Blanco (email@example.com) is senior research analyst for automotive electronics at Gartner Dataquest Research.
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