BQ27Z558: Cannot unseal after seal

Junyu Lu

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

7 months ago

0 Alan Frias 7 months ago

TI__Mastermind 39005 points

Hello,

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

Thank you,
Alan

0 Jonny 7 months ago in reply to Alan Frias

TI__Mastermind 27421 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 Junyu Lu 6 months ago in reply to Jonny

Prodigy 20 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 Junyu Lu 6 months ago

Prodigy 20 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

0 Junyu Lu 6 months ago in reply to Junyu Lu

Prodigy 20 points

I take this back. It is random, sometimes I can unseal but sometimes I cannot

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BQ27Z558: Cannot unseal after seal