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BQ27Z558: Cannot unseal after seal

Junyu Lu
Prodigy 10 points
Part Number: BQ27Z558

Tool/software:

Hi,

I’m testing the seal/unseal commands on the BQ27Z558, but I’ve run into an issue. After sending the seal command (Manufacturing command 0x0030), I’m unable to unseal the device.

Here’s a simplified version of my golden image sequence:

;--------------------------------------------------------
; Unseal device
;--------------------------------------------------------
W: AA 00 14 04
W: AA 00 72 36
W: AA 00 FF FF
W: AA 00 FF FF
X: 1000

;--------------------------------------------------------
; Seal device
;--------------------------------------------------------
W: AA 00 30 00
X: 1000


I checked the Security Keys (0x0035) and confirmed they’re still set to the default values.

I also verified the OperationStatus (0x0054):

Before seal: Full Access

After seal: Sealed

After unseal sequence: Still Sealed (unseal didn’t work)

Am I missing something here?


Thanks
  • 0
    TI__Mastermind 26765 points

    Hello,

    This question has been assigned and will be reviewed when possible.

    Thank you,
    Alan

  • 0 in reply to Alan Frias
    TI__Mastermind 24931 points

    Hello, 

    The Unseal sequence above looks to be correct. Ensure that the unseal and unseal FA keys are the default values, and ensure that the gauge is not being reset, as this will cause the gauge to seal again. 

    Regards, 

    Jonny. 

  • 0 in reply to Jonny
    Prodigy 10 points

    Hi Jonny,

    After some further investigation, it seems that the seal command sometimes works, but other times it does not. I’ve probed the signals with an oscilloscope, including the I²C lines, and they look clean and essentially identical between successful and failed attempts.

    Is there anything specific about the BQ27Z558 that I might be missing—some timing requirement or hidden state—that could cause this intermittent behavior?

    Thanks,

  • 0
    Prodigy 10 points

    Hi Jonny,

    I have done some tests and found that if I have at least 2s delay between seal and unseal then I can have a stable unseal process.(even 1s is not enough) Does that make sense to you?

    Thanks