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Original question:

BQ78350: Why does the remaining capacity drops suddenly from 75% to 7%?

BQ78350: Fixed EDV configuration: Capacity drops to 7% EDV2 point before it is reached

John Batikian
Prodigy 120 points
Part Number: BQ78350

I am trying to configure the bq78350 for fixed EDV, but I am receiving a large discontinuing in RSOC when discharging. It drops from 43% to the EDV point 7%.

I set the EDV values as follows:

EDV0: 2750

EDV1: 3075

EDV2: 3195

 

Why does the pending EDV report ~3534-3524 and then go down to 3455 at the 7% RSOC reset? Near the end of the log I see the pending EDV go to 2750.

The first time that I discharged after setting up the fixed EDV values it did not change the learned full charge capacity, but after another discharge it changed it.

I have attached the logs for the first discharge and second discharge after setting the fixed EDV values.

 /cfs-file/__key/communityserver-discussions-components-files/196/1185.20180601_5F00_nano_5F00_discharge_5F00_u48_5F00_goodBattery.xlsx

/cfs-file/__key/communityserver-discussions-components-files/196/1300.20180601_5F00_nano_5F00_discharge_5F00_u48_5F00_goodBattery2.log

 Did I configure the gauge for fixed EDV correctly? Is fixed EDV enabled with the following CEDV gauge configuration settings?

Thanks,

John

  • 0
    TI__Guru 54715 points
    Hi John,
    In the first log the design capacity is large. The passed charge is not a significant part of the large capacity, so when the EDV2 point is reached and the gauge sets RSOC to 7%, there is a big step in RSOC. There is no learning since the discharge did not start from a full condition. When discharge starts, Fixed EDV2 is 3171 but pending EDV is 3532 and is adjusting, so no, the gauge is not set to used fixed EDV. To used fixed EDV, clear the EDV_CMP (Bit 3) bit in the CEDV Gauging Configuration parameter in data memory, it is shown set in the picture above..

    The second log uses a smaller design capacity. Again as discharge starts, the Fixed EDV2 point is 3195, but the pending EDV is 3533 and adjusting, so again it is not using fixed EDV. Your fixed EDV points are different from the other run.

    You can calculate passed charge as the sum of the current x the elapsed time on a discharge of a fully charged battery. From that you can calculate the capacity for 7% and 3% and find the voltages to enter in the parameters. I expect this is how you arrived at the 2750, 3075 and 3195 values.
  • 0 in reply to WM5295
    Prodigy 120 points
    Setting EDV_CMP to 0 did the trick. Thank you.