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BQ78Z100: SoC rapidly drops down to 0%

Jun Ishida
Expert 5640 points
Part Number: BQ78Z100
Other Parts Discussed in Thread: BQSTUDIO, GPCCHEM, GPCRB

Hi team,

The customer observed an abnormal behavior that the SoC suddenly dropped down to 0% from 18% when the remaining time came down to around 50mins (SoC 18%). However, in such a situation, the voltage was correctly output to CUV and the discharge current flowed without any problem, What's happening on the device inside? Could you tell us what the workaround or the correct register settings is to remove such a behavior?

Regards,

Jun

  • 0
    TI__Guru* 76230 points
    Hi Jun
    We will need further information to be able to tell what is going on. Can the customer reproduce the issue while connected to bqstudio and logging the data. Provide the log data and gg file extracted from the device.

    Also, do you know what the conditions, like temperature were when the SOC drop occurred? Did your customer have learning completed on this pack prior to deployment to the field.?

    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    TI__Expert 5640 points

    Hi Onyx-san,

    I have just received the customer's log data as attached. They are saying that the basic conditions are also included in the file. Please see it and provide the workaround of the SoC drop.

    ★SOCと残時間測定_201904_V2.0No.3.log

    Regards,

    Jun

  • 0 in reply to Jun Ishida
    TI__Guru* 76230 points
    Hi
    did the customer perform a learning cycle? Are they using the correct chem id that was identified using gpcchem?

    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    TI__Expert 5640 points
    Hi Onyx-san,

    1. Does the learning cycle mean the setting of FAST_QMax_LRN? Currently the set-up is 1.
    2. They uses LicoO2 so the chemi-ID is 1580. Please let us know how to confirm the actual setting of chemi-ID?

    Regards,
    Jun
  • 0 in reply to Jun Ishida
    TI__Guru* 76230 points
    Hi Jun
    No. Learning means update status would have been changed by the gauge to either 06 or 0E. To successfully carry out learning, ps follow the app note below.

    www.ti.com/.../slua777


    How did they determine the correct chem id for their application? Did they run gpc chem? Did they program the correct chem id on the gauge after identifying it using gpcchem? You can send the chem id command to the gauge to see the chem id programmed on the device

    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    TI__Expert 5640 points
    Hi Onyx-san,

    The customer is still checking your answer but further questions have just arrived to us. Could you check the below and provide the answer to us?

    1. Should we check the update status of learning cycle per each step? We think that it is no problem with learning cycle if the update status is finally 0x06, but is that understanding correct?

    2. In case that the Ra Table data which the learning cycle is correctly completed is used, is there possibility of failure or abnormal behavior if the battery is an unstable product like prototype or sample in spite of the correct Ra Table data?

    3. What is the difference between Cell0 R_a*, Cell1 R_a*, xCell0 R_a* and xCell1 R_a* in Ra Table, respectively?

    4. The customer has identified the chem-ID with 1580 for LicoO2 battery, but could you tell us how to directly check the actual chem-ID from BMS?

    Regards,
    Jun
  • 0 in reply to Jun Ishida
    TI__Guru* 76230 points
    Hi Jun,

    1. No you do not need to check each step. Run the test and then see if you get 06 at the end. Make sure to log the registers using bqstudio
    2. I would not expect failure at room temperature if learning successfully completed. If you have failures at cold, the gauge can be optimized for lower temperatures using our online gpcrb tool.
    3. These are the resistance tables of cell 1 and cell 2. The gauge has a pair for each of the cell which it alternates writing to to avoid flash wear out.
    4. you go to the chemistry tabof bqstudio and scroll through till you see 1580, you select that and then program to the gauge. after doing that you run a learning cycle following the app note i attached earlier.

    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    TI__Expert 5640 points

    Hi Onyx-san,

    Thank you for your answer. Regarding #1, is 0E also available for correct value at the end as well as 06? The customer thinks both 06 and 0E are correct status at the end.

    Regards,

    Jun

  • 0 in reply to Jun Ishida
    TI__Guru* 76230 points
    Yes, 0E is correct as well. It just means learning has occurred and cell balancing is enabled.

    thanks
    Onyx