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bq20z65-r1: No charge termination

Stefan Knieling1
Prodigy 120 points
Other Parts Discussed in Thread: BQ24735, BQ20Z65-R1

Hi! I use the bq20z65-r1 as Fuel Gauge and the bq24735 Charger IC. I want to charge a 5000mAh LIPO....all  looks like fine, but i think the charge termination doesn't work properly. The cell voltages are: 4174mV, 4175mV and 4182mV...the charging current on currentmeter displays only 5mA...but the bq20z65-r1 doesn't initiates the charge termination. Settings for Taper Current and Quit Current are set as default (250mA and 10mA) but the FC-Flag doesn't raise.....

By the way: Is it the normal charging algorithm that the charging current drops before reaching the cell voltage of 4,2V? Before reaching 4V per cell the charging current was about 3,5A. Later obove 4V the charging current drops nearly linear....and my cells doesn't reach 4,2V...but the LIPO seems to be fully charged.


Please have a look at following screenshots:

For the case I don't calibrate the bq20z65-r1 in the right way, should i recalibrate the bq20z65-r1? Is it possible to disable the IT-Enable command for the recalibration?


Thank you for help, and greets from Austria


Steve

  • 0
    TI__Genius 10235 points

    Yes, you do need to calibrate the gauge first. This step is very important. You can disable Impedance Track by writing 00 to the Update Status data flash register and resetting the gauge (command 0041 to address 00). Don't forget to re-enable Impedance Track after calibrating.

    It is normal for the current to drop as the battery voltage gets higher. This is called CC-CV (constant current-constant voltage)charging and is the most common and recommended method for LION cells. The reason you may be having problems with taper may have to do with the Taper Voltage. This value is pretty small. Try increasing this to 150mV or 200mV and see if you have success.

  • 0 in reply to Chase7071949597
    Prodigy 120 points

    When i try to disbale Impedance Track by writing 00 to the Updates Status data flash register, i get an run-time error '13': type mismatch and the bq-easy software crash... so is there any other way to disable Impedance Track?  

  • 0 in reply to Stefan Knieling1
    Prodigy 120 points

    Dear TI employees, i can't write 00 to the Update Status data flash register, because of a run-time error '13': type mismatch.....what can i do?

    Meanwhile, i found  another way to raise the FC-bit: In data-flash -> charge control -> i set the value of FC Set % to 100%...so the FC-bit is set when "Absolute State of Charge" reach 100%. After the FC flag raised, i followed the instructions for the Qmax and Ra_Table Update, but it doens't work....UpdateStatus is still 04 and MaxError is still 100%......so i want to calibrate the fuel gauge IC again, so i hope you guys could help me to find out what the problem is when i try to set the Update Status to 00. 

    Another strange thing is, that the fuel gauge displays no current or average current during charging .....is this normal?

  • 0 in reply to Stefan Knieling1
    TI__Genius 10235 points

    First, check a few things:

    1) Make sure the device is unsealed.

    2) Make sure there are no permanent failures.

    3) Make sure the battery voltage is above the Flash Update OK Voltage.

    If that doesn't fix it, try unistalling and reinstalling EVSW.

     

    No, it isn't normal for current to report 0 during charge. Check the calibration parameters and make sure they are reasonable (i.e. if CC Current and CC Gain are not similar to your sense resistor value, something is wrong).

  • 0 in reply to Chase7071949597
    Prodigy 120 points

    Hi!

    The device is unsealed, i don't have permanent failures and my battery voltage is above Flash Update OK Voltage....however, i'm able to do write and read operations to the data flash except the update status....it's strange and meanwhile frustrating....

    I use another PC with WinXP, but there is the same problem "runtime error 13: type mismatch"....

    Does it make sense to recalibrate the bq20z65-r1 altough Update Status has value 04?