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BQ27441-G1: OTP Behavior

SSch
Prodigy 20 points
Part Number: BQ27441-G1

Is it possible for the BQ27441 to enter an OTP PROGRAMMING state, similar to the BQ27411? If so, what conditions would cause this state transition to occur?

For our BQ27441 installation, on POR the ITPOR bit is set in the CONFIG_STATUS register, but the values loaded from ROM do not match those in the Technical Reference Manual:

What we actually read: 

  • Design Capacity: 424
  • Design Energy: 1588
  • Taper Voltage: 3200
  • Taper Rate: 4

It appears that bits have been knocked down from the pre-programmed ROM values, suggesting that ROM is being unintentionally accessed and modified at some point. These values are always the same on subsequent POR.

The BQ27441 data briefly references some OTP capability but this is not mentioned in the Technical Reference Manual or other documentation. The BQ27441 does not appear to have a PROG pin.

  • 0
    TI__Guru 53616 points

    The bq27441 has OTP that is pre-programmed by TI. As it's OTP, it can't be arbitrarily re-programmed in the field hence it was removed (with some references still in the collateral) from the documentation. The GPOUT pin can be internally multiplexed as a PROG pin but as I said, this isn't meant to be used outside TI.

  • 0 in reply to Dominik Hartl11
    Prodigy 20 points

    We understand that this is not meant to be used and we do not intend to use it, but can you provide any detail on either the hardware mechanism or how the firmware state transition to OTP occurs?

    We have been referencing the BQ27411 to see if we can glean any details of the OTP state entry, but neither the state machine diagram in the TRM nor the descriptions in the datasheet describe how this occurs.

  • 0 in reply to SSch
    TI__Guru 53616 points

    The gauge must be instructed to stop running the gauging FW and enter a maintenance firmware (which is stored in on-chip ROM). The actual transition is the same between the bq27411 and the bq27441 (see the .ot.fs file from a bq27411 for the I2C command sequence).