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BQ27426: The increase of SOC becomes faster in about 143 minutes when charge starts

user4369354
Expert 1220 points
Part Number: BQ27426
Other Parts Discussed in Thread: BQ25601, GPCCHEM, BQSTUDIO

Dear Sir,

When four types of batteries with different capacities are charged with the combination of BQ27426 (GG IC) and BQ25601 (Charge IC), the increase of SOC becomes rapidly in about 143 minutes in each case.
What is the cause of this behavior?

200210_Charge_BQ25601.xlsx

Best regards,
Chiaki Endo

  • 0
    TI__Mastermind 24870 points

    Hello Chiaki,

    Make sure you guide your customer through the EVM user's guide.

    We need to use GPCCHEM, learning cycle first.

  • 0 in reply to Kang Kang
    Expert 1220 points

    Hello Kang-san,

    We have already confirmed GPCCHEM using EVM.
    Please refer to the following thread for the confirmation result.

    We use the CHEM ID 1202 for the product (attached charge characteristics of Excel).
    Based on this, please confirm the cause of the increase in SOC.

  • 0 in reply to user4369354
    TI__Mastermind 24870 points

    Hello Chiaki-san,

    That is the default chemID. I'm assigning this to an engineer to check.

  • 0 in reply to Kang Kang
    TI__Guru 61006 points

    The gauge uses a model of the cell to run capacity simulations. The result of these simulations is FCC, RM, SOC, etc.

    During charging, the gauge will run these simulations at the beginning and the end and for every change in temperature by "DODatEOC Delta T" (/10).

    A change in temperature can significantly affect FCC and as a result the gauge will either have to report a jump in SOC (if both FCC and RM change due to the temperature triggered capacity simulation) or it will have to smooth this jump.

    Your file indicates that FCC and RM changed so that the smoothing algorithm kicks in so that the gauge will artificially adjust SOC upwards fairly quickly. This usually does not happen that drastically so this suggests that maybe the ChemID (=cell model parameters) isn't a good match or a learning cycle wasn't completed correctly.

    You showed a RUPDIS screen shot. If that happened during a learning cycle, then the gauge calculated a negative impedance. This happens for example, if the measured cell voltage during the learning cycle is above the cell model OCV for the depth of discharge for the impedance value that the gauge was about to update during discharge.

    Please try to run a clean learning cycle. Follow the relax/charge/relax/discharge regimen from 4.2, http://www.ti.com/lit/an/slua777/slua777.pdf. This was written for another gauge but the actual cycle sequence is the same. You do not have to send any specific commands.

    Follow this sequence:

    * start with a cell that is almost empty (e.g. relaxed voltage between 3000mV and 3100mV)

    * reset the gauge

    * configure the gauge (see http://www.ti.com/lit/ug/sluubn3/sluubn3.pdf)

    * follow the sequence from 4.2.2 on. Some of the status bits have different names/locations in the bq27426.

    Once this has completed, both Ra and QMax should have updated. Try the charge test after this. This will likely fix your issues.

  • 0 in reply to Dominik Hartl11
    Expert 1220 points

    Hello Dominik-san,

    (1) Where  is ""① first, ② last, ③ temperature change"" of the simulation execution point  (FCC / RM is updated)?
    　Please fill in points ① and ③ in the table.

    (2) Why are FCC and RM changed due to learning cycle is not completed?
    (3) Why is the FCC decreasing rapidly?
    (4) What is the trigger that updates the FCC when SOC = 100%?
    (5) What is the trigger that updates the FCC when the termination current reaches 60mA?

    200213_Charge_BQ25601.xlsx

  • 0 in reply to user4369354
    TI__Mastermind 24870 points

    Hello Chiaki-san,

    1. Temperature change is due to the DOD at EOC Delta T setting to correct for DOD at the end of charge.

    2. This is because of normal behavior of Impedance Track. Refer to: http://www.ti.com/lit/an/slua364b/slua364b.pdf

    3. FCC is not decreasing rapidly. Pay attention to the units. This is due to RSOC smoothing feature, it is trying to convert to the 100% point. Without a bqStudio log, it is tough to determine any calculations.

    4. FC bit set

    5. That is DOD at EOC update