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BQ34Z100EVM: Huge capacity readback difference after battery connect/disconnect and/or after fuelgauge on/off

Padam Swar
Intellectual 360 points
Part Number: BQ34Z100EVM
Other Parts Discussed in Thread: GPCCHEM, BQ34Z100

I see a huge capacity readback before and after fuel gauge turned off for 1hr.

Is this normal? Is there an explanation?

Steps to reproduce failure (log file, gg and srec file attached)

9:00am Battery fully charged, SoC 100%, charger disconnected 

10:00am Battery relaxed, SoC 100%

10:01am Battery discharged at 285mA, 100% SoC

11:35am Battery discharged at 285mA, 90% SoC

12:24pm Battery relaxed, 85% SoC

12:38pm Battery relaxing, 85% SoC

12:39pm Disconnect battery, Power OFF BQ34Z100EVM

------- continued, disconnected and powered off, no current draw from battery

13:36pm Reconnect battery, Power ON BQ34Z100EVM

13:36pm Battery relaxing, 38% SoC (47% capacity drop???)

14:26pm Battery relaxing, 38% SoC

Same effect is seen on my board. Huge difference when fuel gauge is turned off for  

I see small capacity difference when off or disconnect interval is less than 10 mins

july18.zip

  • 0
    TI__Mastermind 42535 points

    Hi Padam,

    I think its got to do with your chem ID. I see V at chg term to be 3576, if your battery is LFP, please recheck your chem ID and the DOD error from GPCCHEM.

  • 0 in reply to Batt
    Intellectual 360 points

    Hi Batt

    Chem ID 400 was obtained during multiple GPCHEM submissions (attached) 

    2018 Chem ID obtained with TI BQ34Z100 EVM board and battery

    Best chemical ID : 400 Best chemical ID max. deviation, % : 7.58

    Summary of all IDs with max. DOD deviation below 15%

    Chem ID max DOD error, % Max R deviation, ratio
    400 7.58 0.4

    2019 Chem ID obtained with my custom board and battery

    Best chemical ID : 400 Best chemical ID max. deviation, % : 9.99 

    Summary of all IDs with max. DOD deviation below 15%

    Chem ID max DOD error, % Max R deviation, ratio
    400 9.99 0.3

    I do see a need to revise BH and BL thresholds.

    Given the attached datasheets of LFP battery pack and cell, do you recommend any other parameters be adjusted? 

    Thanks

    Padam july22.zip

  • 0 in reply to Padam Swar
    TI__Mastermind 42535 points

    Hi Padam,

    BATHI and BATLOW are nothing but indications. Your settings are OK. On battery disconnect and reattach, the gauge will try to estimate OCV as it sees a voltage across the cell connection. Since the LFP battery has a large flat region, the error in this region can be high. So, in effect, it would be better to not disconnect the battery during use if possible.

  • 0 in reply to Batt
    Intellectual 360 points

    Thank you.

    Battery disconnect is something done to TI EVM to reproduce what is happening on my equipment. 

    My equipment periodically goes to its Sleep Mode (5 min wake, 3hrs sleep) where it has battery connected but power to FuelGauge and all other ICs is disconnected bringing system current < 50uA. 

    Now I am considering bq34Z100 Full Sleep mode instead of turning power off to FuelGauge.

    Do you think this can mitigate SoC jump issue introduced by power on/off to bq34Z100 ?  

    My system Sleep Mode will trigger bq34Z100 Full Sleep mode (3hrs)

    My system Run mode will trigger bq34Z100 Normal mode (5 mins)

  • 0 in reply to Padam Swar
    TI__Mastermind 42535 points

    Yes, it may be able to mitigate it.

  • 0 in reply to Batt
    Intellectual 360 points

    Thanks. It seems to mitigate it.