EEVblog #517 – Car Airbag Controller TeardownPosted on September 10th, 2013 11 comments
What’s inside a modern car airbag controller?
This is is from TRW and comes from a late model Hyundai.
A big thumbs UP!
Worked some years ago in the car industry and one of my first assignments was to dubble check the tightning of external G-sensors.
The big diode is most probably a zener diode to protect against voltage spikes on the power supply line.
I’ve seen similar parts used in other ECUs.
There a very stringent requirements for surviving a broken generator, loose cables… stuff like that.
An interesting vblog for one working in the auto industry. We call the pins in the connector “action pins”, and yes, they are very reliable for unsoldered pins, having to withstand vibration and thermal tests and over 10 years of continual use in a wide variety of environments. The 8400uF capacitor is probably used to fire one or more pyrotechnics independently of the main battery supply. Power for writing to the EEPROM would be supplied by the smaller supply capacitors in the event the battery being unavailable.
As a firefighter, our training teaches us that the capacitor is for firing the airbag in the event of a power failure. Should the impact destroy the vehicle’s battery (which commonly happens), there may not be a 12V source to fire the airbags. In a serious crash, we always disconnect the vehicle’s battery to remove the power source for the airbag. They can still fire for some time, however, due to the capacitor. As extrication efforts can cause stress and motion to the vehicle, it is possible for the airbag to deploy as we’re working on the vehicle. I’ve never seen it happen personally, but it is possible.
I imagine the capacitor enclosure is to prevent it from breaking loose during impact. The forces of impact can be considerable and with the large mass of the capacitor, inertia could easily rip it free from the board.
Also, the sensors need to have proper orientation, obviously, to identify the angle of impact. Early airbags only deployed during a front-end crash. Newer systems can deploy from almost any angle – for side-impact bags, airbags in the seats, ceiling, knee-airbags in the dash, etc. The processors identify the angle of impact and fire only the appropriate bags.
Dave, great teardown! Just to help you finish identifying major components se my comments below:
MS84 (in 64-pin TQFP package) is an ASIC responsible for two things: 1 – fireing (and diagnosing) squibs; 2 – communication with external acceleration and pressure sensors.
The 8-pin device in SO package (the one next to the crystal and MS84) is a N-channel MOSFET. It is very low Rdson transistor connected on high side power path. It has built-in charge pump so it can be driven by a 5V logic level signal.
Great teardown, have been on the lookout for that ever since it’s been in your mail. Thank you.
TRW is a customer of us and I was able to visit their plant for ABS-valves. A huge clean room, perhaps not up to silicon standards but still beyond anything I’ve seen in the automotive sector, which is already pretty clean and tidy.
Lovely teardown Dave!
I’d hazard a guess that the board wasn’t dipped in the conformal-coating to avoid conductivity issues with the press-fit/non-soldered pins. They wouldn’t dip the board with that large connector in place, and with conformal-coating in the pin-holes, they might not have gotten reliable connections.
I manufactures these units, interesting seeing this popup, and you preaty much got how the unit works.
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