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BQ78350-R1: Disable battery capacity learning

Gary Bloomfield
Prodigy 100 points
Part Number: BQ78350-R1
Other Parts Discussed in Thread: BQ76930EVM, BQSTUDIO, BQ78350

I have Li-ion battery packs, based on the bq76930EVM design, that (after several charge/discharge cycles) need to be discharged to below 3V per cell before the charge FETs turns on and I can charge to 4.2V again.  This is without the battery capacity learning cycle being performed.

Is there a way to disable battery capacity learning and only use OCV for capacity? 

Or, is battery capacity learning a "must do"?

I would be happy to just put the pack on a smart charger and have charging stop when the pack voltage reached the charge voltage.

  • 0
    TI__Guru* 81034 points

    Hi Gary,

    I recall you were facing this issue a few months ago - is this the same issue you were facing before?

    https://e2e.ti.com/support/power-management/f/196/t/860481

    We need to figure out what is preventing the CHG FET from closing. There are a number of protections that might cause this. Are you able to collect a log file showing this behavior? If you are able to connect to BQStudio, you can click the 'Start Log' button which will log all of the important status registers we need to see to determine what is happening. Can you also send your data flash settings (click on the 'Export' button in the Data Memory screen of BQStudio)?

    Thanks,

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 100 points

    Hello Matt,

    Yes, it's the same issue. 

    It could take some time to get a battery pack from the field that is experiencing the issue.  But I will send you the downloaded status information when it available.

    Is it a requirement that you have to train the battery packs (with the BQ chip), make a golden file, and program the information into production packs.   Or, is there a way to disable battery learning? 

    Attached is the latest data flash configuration file programmed into the packs.

    Thanks for your help.

    Gary

    03Oct2019 BMS Configuration File.gg.csv

  • 0 in reply to Gary Bloomfield
    TI__Guru* 81034 points

    Hi Gary,

    Thanks for sending your data flash file. Normally, battery gauging would not explain why the CHG FET will not close. Going through the process of setting the ChemID and characterizing the CEDV parameters is necessary if you want accurate SOC reporting, but it is not required.

    A log file will help to determine the issue, but here is what I can see from your data flash settings:

    • In the Enabled Protections C register, Overcharge, PTO, and CTO are disabled. I was thinking maybe overcharge could cause the FET to disable, but since you have these protections disabled, it is not likely causing the issue.
    • I notice you have TS1 set up to measure FET temperature and the [OTFET] bit in the FET Options register is set to '1'. One possibility is that a high temperature on the FET may be causing the BQ78350 to open it since the OTFET bit programs it to do so.
    • The [CHGFET] bit in FET Options is also set to '1'. This programs the CHG FET to open when valid charge termination is detected. This is something you should look at to make sure the charge termination parameters are set properly for your battery. If it was mistakenly detected, it would open the CHG FET. 
    • The OTC threshold is set lower than the default value. Check to make sure an over-temperature during charge fault is not being triggered.
    • The SLEEPCHG bit is set to '0' which turns off the CHG FET in Sleep mode. I doubt the device is in Sleep mode when the charger is connected, but something else to check. 
    • I recommend checking section 5.5 of the Technical Reference Manual for a list of conditions that can open the CHG FET.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 100 points

    Thanks for your help Matt.