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BQ27Z561EVM-011: Learning cycle status not updated from 0x05 to 0x06 even though REST is achieved

Ofer Rivkind
Prodigy 40 points
Part Number: BQ27Z561EVM-011

I'm trying to run a learning cycle on my LP-502535-1S-3 3.7V 400mAh 1.48Wh battery.

I have obtained a ChemID based on sluuc94.pdf.

I'm following your slua093.pdf document for the learning cycle. Everything went ok until stage 3.2.5, discharging to empty.

But at stage 3.2.6, even though REST was achieved, VOK did not clear and the Update Status did not update from 0x05 to 0x06.

I'm discharging with a ~56ohm resistor, so my discharge current is in the range of -70mA when the battery is fully charged to ~-40mA when nearly empty, at 2.75V.

I have run a learning cycle on a very similar battery with the exact same charging and discharging conditions before and then everything went ok.

Why would the status not update to 0x06?

The register and data memory logs are attached in the RAR file.

Thanks,

OferTraining Sequence logs.rar

  • 0
    TI__Expert 8245 points

    Hi,

    It looks like you are getting an OCV measurement but QMax is not updating. This is due to one of the following conditions that trigger a QMax disqualification.

    I suspect that offset error is the culprit here as your log file does not suggest a violation of any of the other conditions. You said that your SNS resistor is 56ohm? Can you share the rest of your schematic?

    Best Regards,

    Jackson

  • 0 in reply to Jackson DiGiovanna
    Prodigy 40 points

    Hi,

    There are no schematics. For the entire process (obtaining ChemID and perform the learning cycle) I am using the bq27z561EVM-011 as-is.

    My battery is connected to BAT+ and BAT- on the J2 jack.

    To charge the battery I am connecting a power supply set to 4.2V and 200mA current limit to BAT+ and PACK- on the J1 jack.

    To discharge, I am connecting the mentioned 56ohm resistor between BAT+ and PACK-.

    The SNS resistor of the fuel gauge is the one on the EVM.

    I have since started another learning cycle from scratch and will start the problematic discharge stage at the end of this day, which reach the critical point (rest and hopefully QMax update) tomorrow.

    What can I do to make sure it succeeds this time?

    Thanks,

    Ofer

  • 0 in reply to Ofer Rivkind
    TI__Expert 8245 points

    Ofer,

    You should connect your Power Supply to PACK+ and PACK-. For these type of tests we usually use a programmable load and set it to the desired discharge rate and have it terminate discharge when empty. We use this method because it provides a more constant discharge rate than simply using a resistor. This way you can achieve a cleaner discharge current that does not jump around. This isn't important normally but during a learning cycle and when selecting a ChemID it is vital to have clean constant chg/dsg rates.

    I suspect that because of the method you are using to discharge, enough error is accumulating to disqualify a QMax update as your current varies from -45 to -79mA throughout discharge.

    Best Regards,

    Jackson

  • 0 in reply to Jackson DiGiovanna
    Prodigy 40 points

    How can I obtain this programmable load you are using so I can have a fixed current during discharge?

    Thanks,

    Ofer

  • 0 in reply to Ofer Rivkind
    TI__Expert 8245 points

    Hi Ofer,

    I can not make official recommendations but we use Keithley SMUs that can supply a constant current with a voltage compliance for situations like this. The Keithley will automatically adjust the supplied voltage so that as the battery discharges and the voltage drops, the current will remain the same. You could also use any programmable DC supplies that are capable of supplying constant current.

    Best Regards,

    Jackson

  • 0 in reply to Jackson DiGiovanna
    Prodigy 40 points

    Hi Jackson,

    Continuing this case, I obtained a platform that can allow me to discharge the battery at a constant current throughout. I started from scratch and obtained a new ChemID and then restarted the learning cycle again. I discharged the battery to empty, let it relax, charged it to full and let it relax again (sections 3.2.1 through 3.2.4 in slua903). Even though I obtained a REST status after the charge VOK did not clear (RDIS did clear). Status did update to 0x05.

    Your documentation says VOK should have cleared so I don't know if I have a problem or not. I will continue with the discharge stage and hope for the best but perhaps I already have a problem and I will only fail again at the end of the discharge.

    If this is indeed a problem please let me know, and what I can do about it. I've performed learning cycles on a few similar batteries before but never encountered any such issues.

    I will point out that during the previous run, the run that strated this question thread, the problem with VOK was indeed only during the discharge; charging was ok (I went back and checked the logs).

    I'm attached the register log with which I obtained the ChemID and the logs of this charge cycle.

    Thanks,

    Ofer5417.Charge.rarChemID_2023_02_12.rar

  • 0 in reply to Ofer Rivkind
    TI__Guru 57747 points

    Hello Ofer,

    Jackson is out on work for a few days, so there will be a delay in reply

  • 0 in reply to Shirish
    TI__Guru 57747 points

    Hello Ofer,

    Just want to confirm that the gauge was accurately calibrated before the cycling.

  • 0 in reply to Shirish
    Prodigy 40 points

    Hi Shirish,

    Yes, it was calibrated following your procedure for voltage and current calibration in sluubo7.pdf, chapter 12.