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BQ79606A-Q1: SM402 and SM302 is required or not for battery protector?

Zizhen Yu
Prodigy 120 points
Part Number: BQ79606A-Q1

Tool/software:

Hi TI Team:

In safety manual, the SM302 and SM402 has a note(This diagnostic is not required to meet the ASIL-B goal for the secondary protectors.), as shown in following picture.

But in FMEDA, they have been used to cover some failure modes, for example SM402:

So I want to know the meaning of "This diagnostic is not required to meet the ASIL-B goal for the secondary protectors"

Why these diagnostic is not required to meet the ASIL-B goal for the secondary protectors and how to understand the note?

  • 0
    TI__Expert 6720 points

    Zizhen,

    As ASIL-B has less stringent requirements than ASIL-C or ASIL-D, certain safety mechanisms can be omitted and still meet the requirements. Especially complicated and redundant safety mechanisms (as these are) may be elected to be cut first. If you are using the BQ79606 in a system that is only being designed to meet ASIL-B standards you can cut these safety mechanisms and still meet that standard.

    Regards,

    Ben

  • 0 in reply to Benjamin Luty
    Prodigy 120 points

    Hi Benjamin:

    Thank you for your answers.

    It's very clear for me, but I still have a question need your clasification.

    If I cut the SM402 and SM302 for an ASIL B system , then in the FMEDA calculation tool, these failure modes shown in following picture has no corresponding safety mechanisms to cover, is it OK for met ASIL B requirement? How do I deal with these failure modes?

    Thank you.

  • +1 in reply to Zizhen Yu
    TI__Expert 6720 points

    Zizhen,

    After removing safety mechanisms you want to remove, then you will have faults that are not covered. The fault metrics in the "Totals-ISO26262" tab should be used to determine whether you meet your target ASIL rating (ASIL B in this case). It is okay to leave faults uncovered, as long as the "Totals-ISO26262" tab meets your target fault metrics. 

    Regards,

    Ben