• State Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 2 answers
  • Subscribers 63 subscribers
  • Views 654 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ40Z50-R2: I can't seem to get my gas gauge to work correctly

Matthew Benefiel
Prodigy 60 points
Part Number: BQ40Z50-R2
Other Parts Discussed in Thread: BQ40Z50, BQSTUDIO, BQ20Z655-R1

I created my own boards using the BQ40z50-R2 eval board circuit design and so far all the voltages and currents are accurate and working as designed. However my gas gauge is not updating correctly. In the gag gauging registers I've set all cells to 5000mAh which is my battery pack (4S2P). When I charge I have the LEDs turn on and it tracks somewhat but ends up with some low calculated mAh around 300-1700mAh, as shown in the remaining and full charge capacity registers. Eventually the gauge will show 100% charged. When I go to discharge the remaining capacity and full charge capacity reset to zero and the charge icon stays at 100% and all 5 LEDs stay on through the full discharge until I go to charge again. At that point it updates but still never makes it to the 5000mAh. I've been through four or five full discharge and charge cycles and still will not track properly. I've dug through the technical reference and tried different register settings and still can't figure out what I'm missing. I've attached my register settings. I did try changing the Load Select to 1 from 7 and still see no change. Any help trying to figure out how to properly setup the gas gauge would be appreciated.bq40z50-R2 Configuration File 201800803a msb.gg.csv.zip

  • 0
    TI__Expert 6575 points
    Hi,
    It is possible that the chemistry ID programmed might not be correct for your pack.
    You can use the online tool at http://www.ti.com/tool/GPCCHEM and follow the included instructions to make sure that you are using the correct chemID.
    I would recommend checking that the cell voltage and current calibration is correct for your board using the "Calibration" tab in bqStudio, before collecting the data for the chemID.
    Regards,
    Swami
  • 0 in reply to Swaminathan Ramanathan75031
    Prodigy 60 points

    I am currently using the Samsung INR18650-25R but as a 4S2P, so a 5000mAh. I used that ChemID, but I'm not sure I've setup the registers correctly after that. I realized that I had my FD, FC, TD, and TC wrong, but I don't understand why the gas gauge clears out when I go into discharge. Yesterday I was discharging and it stayed at 100% at a 5amp discharge (starting around 15V stack voltage), I then shut of the load after 10 minutes and the gauge dropped to 0% and I was still int the 14V range. Does the gas gauge require a few full discharge/charge cycles to properly calculate? It seems with the old bq20z655-R1 the remaining capacity updated immediately based on register changes, I'm not seeing that with the bq40z50-R2.

    I will check out the tool as the final battery I will be using is not a standard off the shelf.

  • 0 in reply to Matthew Benefiel
    TI__Expert 6575 points
    If you can post the gg file from this pack, I can check to see if it is configured correctly.
    Regards,
    Swami
  • 0 in reply to Swaminathan Ramanathan75031
    Prodigy 60 points

    The gg file is the attached zip in the original post, after the last sentence.

  • 0 in reply to Matthew Benefiel
    TI__Expert 6575 points
    The most obvious thing that I see in the gg file is that "Gas Gauging->IT Cfg-> Term Voltage" is set to 9000mV.
    Also, the "IT Gauging Configuration" (set to 0xd0fe) is set for PACK level termination, not cell level termination.
    This seems low for a 4S configuration.
    typically it is ~ 2750mv to 3000mV/cell which would be ~11000mV to 12000mV for the "Term Voltage".
    This can cause issues with the IT algorithm.
    Having the wrong chemID can also cause issues.
    I would check both of these.
    Regards,
    Swami
  • 0 in reply to Swaminathan Ramanathan75031
    Prodigy 60 points

    Thank you for the help, changing the Term Voltage got it working, along with adjusting the FD, FC, TD, and TC. It is tracking and learning the claimed capacity of the cell. Somehow I missed the term voltage when I switch from the default 3S to 4S. It would be helpful to have a quick user guide that could point out the some of the main registers to change based on 1s-4s. It is hard to dig through the datasheet and guide when there are so many features (not that I'm complaining about the features which are nice.

    If you don't mind one more question I'm trying to figure out how to allow charging when the SMBus is not plugged in, right now it stops charging when I do not have the SMBus plugged in and the Battery Management Studio open. Thanks again for the help!