Airbag controller with Safing MOSFET

Airbags have been a standard feature in passenger cars for over 20 years. Naturally these systems need to be extremely robust and reliable, regardless of whether it is just a single airbag for the driver and front passenger or a complete multi-stage airbag system offering a range of protection options (front, side, head, rollover and even pedestrian protection). A Safing MOSFET in series with firing circuit transistors provides cost-effective operational reliability, enabling breakage of the current circuit in case of incorrect operation due to malfunction or electrical noise.

Block diagram

Highlighted components are Nexperia focus products

Design considerations

  • Traditional solutions to Airbag applications are being withdrawn from the market due to unsustainability
  • Enhanced SOA technology provides similar linear mode performance in a sustainable silicon technology
  • For pulsed linear mode applications, such as the Safing MOSFET in airbags, Nexperia’s ASFETs provide the required robustness while delivering significant board space savings (up to 84% with an LFPAK33 device) compared to traditional DPAK solutions
  • Airbag firing circuits need a stable voltage of 15 to 20 V, requiring a boost converter to step up the standard 12 V battery voltage to 25–35 V

Automotive ASFETs for airbag applications

When choosing a MOSFET to regulate the supply voltage to the squibs in an airbag system, the choice has traditionally been limited to older generations of silicon technology, such as the legacy wire-bonded DPAK package. Nexperia have designed a range of Application Specific MOSFETS (ASFETs) to address the specialised needs of airbag applications, focused on enhanced SOA performance for improved linear mode.

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Reverse battery protection in automotive applications

This aim of this interactive application note is to help the reader gain an insight into how to protect 12 V automotive systems from being exposed to a reversed biased battery condition e.g. during maintenance where the battery leads may be reconnected in the opposite polarity.

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