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Automotive Semiconductors and Functional Safety

A safety mechanism with 99% diagnostic coverage is added to a circuit with a failure rate of 200 FIT. What is the failure rate of the faults that remain undetected by the safety mechanism?

  1. A198 FIT
  2. B0.02 FIT
  3. C2 FIT
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Answer: C. 2 FIT

Diagnostic coverage (DC) is the proportion of faults that a safety mechanism can detect or control. The remaining failure rate is 200 × (1 − 0.99) = 200 × 0.01 = 2 FIT. 198 FIT is the failure rate of the faults the safety mechanism can detect, and 0.02 FIT is the result of misplacing the decimal point in the multiplication. Fault coverage in manufacturing test represents the proportion of defective parts found before shipment, whereas diagnostic coverage represents the proportion of faults occurring in use that are detected on the spot.

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