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LM74501-Q1: ISO7637-2 pulse 1 event

Alfie Cheng
Expert 3720 points
Part Number: LM74501-Q1
Other Parts Discussed in Thread: LM74700-Q1, , LM74701-Q1

Hi team,

there is a question I want to consult you. if LM74501-Q1 have no TVS less function, like the device LM74700-Q1, we should add TVS at where to pass the ISO7637-2 pulse 1 event. just curious about that, because I just know there is a TVS behind 12V battery to limit load dump voltage. it means if we use LM74501-Q1, which TVS diode could be removed?

  • 0
    TI__Mastermind 49085 points

    Hi Alfie,

    LM74700-Q1 needs TVS to clamp the negative side of the voltage during ISO7637-2 Pulse 1. This TVS is placed on the input line protecting ANODE/EN pin of the IC.

    In load dump, we do not use TVS to clamp the positive voltage as the device can pass the suppressed load dump without it.

    Sharing LM74501-Q1 response to ISO pulse 1.

    TVS diode used to clamp negative side can be removed and still the test can be passed.

    This is the TVS I am referring to.

    Just in case you want LM74700-Q1 but with a TVS-less operation, we do have LM74701-Q1

    Regards,

    Shiven Dhir

  • 0 in reply to Shiven Dhir
    TI__Expert 3720 points

    Hi Shiven,

    I still not understand that why does the negative voltage will break ANODE pin, from the datasheet of LM74700, the input voltage is from -60V to 60V.

  • 0 in reply to Alfie Cheng
    TI__Mastermind 49085 points

    Hi Alfie,

    Yes, the ANODE pin can withstand -60V in LM74700-Q1, but ISO pulse 1 goes beyond -60V. For a 12V system it can go up to -150V which surely will damage the device.

    Regards,

    Shiven Dhir