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BQ76972: Partially autonomous FET driver how to see if FETs will get enabled autonomously

Slava Takrovskij
Prodigy 10 points
Part Number: BQ76972
Other Parts Discussed in Thread: BQSTUDIO,

Tool/software:

We've the following situation

  1. We sent the ALL_FETS_OFF command on startup.
  2. Reading FETStatus tells us that CHG_FET and DSG_FET are low (0).
  3. We force a fault condition to occur. E.g. disconnecting a temperature sensor.
  4. Through an external input, we sent the ALL_FETS_ON command.
  5. As expected FETStatus still shows that the FETs are turned off.
  6. How do we know if we should resend again with our external input to allow autonomous FET handling again?

Is it possible to read the FET driver mode? So we can know that the FETs will be turned on when the fault condition resolves itself. 
After reading through the Technical Reference Manual for BQ76972 and checking bqStudio, we couldn't find anything that answers that question.

We've looked at Settings:FET:FET Options[SFET] in case that would change, but it didn't. 

Any help is appreciated! 

  • 0
    TI__Expert 4220 points

    Hi Slava,

    Sorry for the late response. The team has limited resource recently.

    Can you clarify your question? What do you mean by 'FET Driver Mode'. Do you mean the FET_EN bit? You can read MANUFACTURINGSTATUS register.

    BRs

    Kian

  • 0 in reply to Kian Lin
    Prodigy 10 points

    Hi Kian,

    That's totally understandable. No worries.

    We're curious about the state in which the FET drivers are. Especially after sending the subcommand ALL_FETS_ON.
    The technical reference manual mentions the following:

    Is there a register we could read to see if a FET is manually turned off by the host for example? Or if it is driven autonomously by the BQ device.

  • +1 in reply to Slava Takrovskij
    TI__Expert 4220 points

    Hi Slava,

    Thanks for your understanding.

    We don't have a register to indicate FET was turned off by BQ or by Host. You can only determine if you want BQ to control FETs autonomously. And you can read 0x7F FET Status() and Safety Status A/B/C to see which protection trigger the FET turn-off.

    BRs

    Kian

  • 0 in reply to Kian Lin
    Prodigy 10 points

    Hi Kian,

    Thank you for the answer. That clears it up for us.

    We'll adjust our implementation in that case.

    Have a good day!