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BQ27520-G4: RM value shifts due to long-term storage

SUZUKI YASUO
Prodigy 20 points
Part Number: BQ27520-G4
Other Parts Discussed in Thread: GPCRA0, GPCRB

When the battery is connected and stored for a long time with the power off, the battery becomes empty due to the standby current, but the RM value is close to a fully charged value. What is the cause?

If the discharge current is high to some extent, the RM value will not deviate, but if the discharge current is small, will the RM value deviate?

  • 0
    TI__Guru 57747 points

    Hello

    It is likely to be a configuration issue that the gauge is not detecting standby current.

    Does the "Initial Standby" current match the system standby current? Is the deadband set below the standby current?

    For more information see TRM 2.13 StandbyCurrent( ): 0x18 and 0x19

  • 0 in reply to Shirish
    Prodigy 20 points

    Hello

     "Initial Standby" is set to -10mA, and "Deadband" is set to 5mA.
    The actual standby current will be 0.6mA.

    Will there be any deviation in this case?

    Also, will the deviation increase if stored in a low temperature environment?

  • 0 in reply to SUZUKI YASUO
    TI__Guru 57747 points

    One option would be to reduce deadband so that standby current is detected but since the standby current is less than 1mA, i don't think that is possible.

    The other option is to use the gauge feature of compute capacity at rest  Please see TRM section 5.1.7 Quit Current, Dsg Relax Time, Chg Relax Time, and Quit Relax Time

    Also please confirm that the correct matching chemistry was programmed to the gauge and learning cycle was completed

  • 0 in reply to Shirish
    Prodigy 20 points

    Thanks

    Quit Current is set to 20mA, Dsg Relax Time and Chg Relax Time are set to 60 seconds, so the device is in relaxation mode.

    The ChemID settings are correct and the learning cycle is complete.
    Does storage in a low temperature environment affect the updating of the Ra table?

  • 0 in reply to SUZUKI YASUO
    TI__Guru 57747 points

    How low is the temperature? For low temperature optimization you can use the GPCRA0 and GPCRB tool.

  • 0 in reply to Shirish
    Prodigy 20 points

    Thanks.
    The environment will be about 0 to 10°C.
    I will consider GPCRB, which also considers low temperatures.