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Transient Thermal Investigation for a SmartMOS Based Airbag Circuit Driver

[+] Author Affiliations
Victor Adrian Chiriac, Tien-Yu Tom Lee, Paul Bennett

Motorola, Inc., Tempe, AZ

Paper No. IMECE2002-39531, pp. 181-188; 8 pages
doi:10.1115/IMECE2002-39531
From:
  • ASME 2002 International Mechanical Engineering Congress and Exposition
  • Heat Transfer, Volume 5
  • New Orleans, Louisiana, USA, November 17–22, 2002
  • Conference Sponsors: Heat Transfer Division
  • ISBN: 0-7918-3636-3 | eISBN: 0-7918-1691-5, 0-7918-1692-3, 0-7918-1693-1
  • Copyright © 2002 by ASME

abstract

A numerical study was conducted to model the transient thermal behavior of an airbag squib driver using commercially available software. The squib driver is part of an airbag deployment IC. The simulations were primarily used to predict the thermal gradient across the die for determining the optimal sensor location for thermal shutdown that would protect the device from destruction. The temperature sensor should be placed such that it gets hot enough for any electrical pulses that heat up the device close to the destruction point. The overall purpose is to provide a thermal detection circuit for disabling current prior to reaching a thermally destructive level. A preliminary wafer level study correlates the simulated and measured values and indicates that the junction temperature is lower for the case with thicker die and adiabatic boundary conditions; an opposite trend is observed for the cases with fixed temperature boundary condition attached to the domain bottom side. The study of the high IC side dissipating 80W for 5 ms indicates that the bottom and top center monitor points reach temperatures of 188.2°C and 130.5°C at the end of the 5 ms timeframe, corresponding to a peak source temperature of 294.6°C. A similar study with 30W uniform dissipation for 20 ms indicates that the peak junction temperature is lower than before (220°C vs. 294°C). The study of the low IC side reveals higher peak temperatures compared to the high side, due to the larger power density for these cases. The peak temperatures are 368.7°C for 50W/5 ms, and 301.8°C for 25W/20 ms. The left monitor point temperature ranges between 210°C–260°C while the right monitor point temperature ranges between 140°C–160°C. The thermal investigation of the package after the thermal shutdown predicted the time needed for the FETs to reach predetermined temperatures for different scenarios. The temperatures of the low side FETs drop by almost 50% within the 30 ms following the 20 ms of constant powering at 50W. When the high-side FETs are powered at 80W for 5 ms then cooled, the temperature rises then decays within 0.1 s.

Copyright © 2002 by ASME
Topics: Circuits , Airbags

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