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BQ40Z50-R2: Question about CFETF and DFETF Permanent Fail and Fuse Blowing

Kevin Banks
Prodigy 235 points
Part Number: BQ40Z50-R2
Other Parts Discussed in Thread: BQSTUDIO

Tool/software:

In the BQ40Z50-R2 Reference Manual (SLUUBK0B) on page 24 it says

The FUSE pin is driven high if configured for specific failures and Voltage() is above Min Blow Fuse Voltage or there is a CHG FET (CFETF) or DSG FET (DFETF) failure.

Does this statement mean a CFETF or DFETF Permanent Failure will drive the FUSE pin high regardless of the settings in the PF Fuse C register? IOW, the fuse blowing is conditional on the Enabled PF C register but not the PF Fuse C register?

Or does it mean that a CFETF or DFETF (if enabled in Enabled PF C and PF Fuse C registers) will drive the FUSE pin high regardless of the Voltage()? IOW, CFETF and DFETF bypass the Voltage() check?

To ask it a different way, which of these modified versions of the text from the Reference Manual is correct?

1. The FUSE pin is driven high if (configured for specific failures and Voltage() is above Min Blow Fuse Voltage) or (there is a CHG FET (CFETF) or DSG FET (DFETF) failure).

2. The FUSE pin is driven high if (configured for specific failures) and (Voltage() is above Min Blow Fuse Voltage or there is a CHG FET (CFETF) or DSG FET (DFETF) failure).

I think the second interpretation is correct, but just want to confirm. When I first read the statement in the RM, I interpreted it the first way, which implies I should not enable/use the CFETF/DFETF Permanent Failures until I am ready to blow fuses.

  • 0
    TI__Mastermind 28470 points

    Hi Kevin,

    CFETF/DFETF will blow the fuse regardless of what is seen from the Voltage() or configuration. This cannot be disabled. Looking into the code, it looks like the first statement, where the voltage and the PF conditions need to be met to trigger the fuse.

    Regards,

    Anthony

  • 0 in reply to Anthony
    Prodigy 235 points

    Thank you for the quick response Anthony.

    Just as a sanity check: so you are saying that the DFETF and CFETF bits shown in the PF Fuse C register by BQStudio have no effect?

    And the DFETF and CFETF bits shown in the Enabled PF C register by BQStudio essentially enable both the Permanent Fail condition AND the blowing of the chemical fuse?

  • +1 in reply to Kevin Banks
    TI__Mastermind 28470 points

    Hi Kevin,

    I believe that the CFETF/DFETF PF can be enabled or disabled by the Enabled PF register, however if they are enabled they will blow the Fuse.

    Regards.

    Anthony