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BQ20Z65-R1: Internal remaining capacity counter reset

Part Number: BQ20Z65-R1

Hi TI Team,

If Over Charge Capacity occurs, the OC bit or Over Charge fault condition can be cleared by a continuous amount of discharge over Over Charge Recovery. But how to reset the internal counter? Discharge the battery to Term Voltage reset it to 0? This is to prevent the OC from being set on the next charge, as we found that the OC was set again once the battery was charged up.

C.4.6.9 Over Charge Capacity (Offset 13)

The ba20z60-R1/bq20z65-R1 enters a overcharge fault and sets the [OC] flag in ChargingStatus if the internally counted remaining capacity exceeds FullChargeCapacity + Over Charge Capacity.

Thanks!

Jeff Ye

TOTEX Manufacturing Inc.

  • There is no counter reset. The gauge will calculate FCC depending on conditions (e.g. load, temperature) and when you start charging, it will also calculate RM and then it'll add measured charges (via the coulomb counter) to RM. RM will also be re-calculated if temperature changes by more than 5deg.C (default) during charging. If RM - FCC exceeds >= the over charge capacity threshold, the gauge will again set the OC bit.

  • Hi,

    I did the following test. It looks like in the event of an OC failure, the battery will always trigger OC before it is fully charged. Smart charger will not charge battery and perform full cycle to calibrate the fuel gauge unless a power supply is used to force charging the battery until taper current.

    Battery info: 3S2P, 6600mAh, OC threshold 660mAh, Term Volatge=8.4V.

    Starting condition: RSOC=80%, RM=5093mAh, FCC=6397mAh

    1.Discharging the battery on the cell side (bypassing the fuel gauge) for 30% to simulate capacity loss due to circuit leakage, RM and FCC remained the same at 5093mAh and 6397mAh.

    2 charge the battery and continue to charge around 10% after RM=FCC, OC and TCA set

    3.Discharged the battery to Term Voltage 8.4V, RM dropped from 1679mAh (29%) to 0, FCC updated to 4230mAh (based on previous discharge).

    4. After RM=FCC, when the battery continues to charge more than 660mAh, OC and TCA are set again.

    How does the battery get out of this situation and update the RM/FCC? Run a calibration cycle or just a rest after fully charged?

    Thanks

    Jeffrey

  • The problem is that you "confuse" the gauge when you prevent it from coulomb counting the actual passed charge and then it miscalculates FCC.

    It'll likely self-correct after relax and discharge and relax.

  • Hi Dominik,

    I think this is a normal storage situation and the supply current in sleep mode causes a loss of capacity. In our case, the capacity may drop by 10% in 6 months, so it will cause an Over Charge Capacity later. The problem is that the RM or RSOC is not updated, I thought it should be updated periodically as per OCV in long term storage. The smart charger can't fully charge the battery due to OC and TCA set, so the fuel gauge can't be calibrated. Can a relax after partial charge update RM and RSOC?

    Thanks!

    Jeffrey

  • The gauge has a specific mode (ship mode) if the product is in long term storage.

    Even in "normal" operating mode, the gauge will eventually take an OCV measurement in relax and adjust its results accordingly. However, this may take a long time, depending on conditions. For example, up to 5 hours if the voltage isn't stable enough in relax or even longer (e.g. relax after charge if charge terminated in the flat region of the OCV).

  • Hi Dominik,

    How much charging or discharging is required before relaxing? I charged the battery by 9% (because 10% would cause OC set) and left it overnight, I didn't see RM update. Maybe need to charge > 30%?

    Thanks

    Jeffrey

  • You need to charge or discharge enough so that the gauge's SOC is <100% and >0%. Please make sure that LOCK_0 is not set.

  • Cfg C is 0x0070, so the bit LOCK_0 is set, let me test that. "SOC is <100% and >0%" means to charge or discharge until RM starts to change, right?

  • The gauge will update remaining capacity and SOC in relax when it takes an OCV measurement but only if the OCV is within the DOD range that was defined by charge termination (=100% SOC) and end of discharge (=0% SOC). Therefore you should charge enough to get it out from an over-discharge state until you'll see a change in SOC.

  • Do you mean to run a full calibration cycle? Charge the battery to primary termination (RM=100%) and than discharge to Term Voltage (RM=0), and than charge back until SOC starts change?  Thanks!

  • No. I meant that you need to charge enough that the state of the cell is below DOD at end of discharge. Then the gauge will update remaining capacity either through coulomb count or during an OCV measurement.