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DRV8844 nFault pull-high level

Abby3626
Intellectual 475 points
Other Parts Discussed in Thread: DRV8844

Hi All,

In DRV8844 EVM, I remove R1, add 10K resistance pull-high to 24V at nFault pin.

But I only can get about 7.5V at nFault pin.

In DRV8844 datasheet, absolute maximum ratings table shows:

Digital pin voltage range: LGND - 0.5 to LGND + 7 (V)  -> I connect LGND to GND

Base on this table, I can't get 24V nFault, right? but why?

  • 0
    TI__Expert 8885 points

    Abby,

    nFault is open-drain type signal, this means during normal condition (no faults) this pin will see the pull-up voltage. SO if you pull-up to 24V, it sees 24V at this pin during normal conditions which is way too high than absolute max 7Volt above GND.

    This is not allowed and may damage the device.

    Best Regards

    Milan-Motor Application Team

  • 0 in reply to Milan Rajne
    Intellectual 475 points

    Hi,

    Thanks for your reply.

    Although nFault is open-drain, because the damage issue, DRV8844 is desinged to limit the digital voltage under 7V?

    In the other word, nFault pull-high voltage con not over 7V.

    Is my understanding right?

     

  • 0 in reply to Abby3626
    TI__Expert 8885 points

    Yes I think designer might have limited it to 7V to protect the FET.

    but As i mentioned, since its beyond the device absolute max rating, continous operation is not allowed.

    Best Regards

    Milan-Motor Application Team