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BQ27542 Learning Cycle in Battery Management Studio not updating gas gauge.

Tyler Barkin
Prodigy 170 points
Other Parts Discussed in Thread: BQ27542EVM, GPCCHEM

Hello, 

I have the BQ27542EVM module set up with some relays to switch in a load or power supply. Discharge is at 1/10C and charge is at 1/3C.  I've ran 3 learning cycles on batteries that are 630 mAh nominal but when I check the gas gauge in Battery Management Studio it is reporting the battery total capacity at above 900 mAh. Additionally the Update Status register doesn't  change from 04 after the learning cycle in the manor that the tech docs suggest it should. I don't understand why the battery stats are so wildly wrong. 

Hardware : BQ27542EVM; 630 mAh lithium ion cell, CPX4000DP Power Supply (for charging cells) set to 4.2V 0.26A limits

  • 0
    TI__Expert 8230 points
    Hello Tyler,

    Couple questions:
    Do you have a log file of the learning cycle you can provide? Have you filled out the Parameter Q&A to set the correct design parameters for your application?

    Also, have you programmed the correct chemID on the gauge?

    Thank you.
  • 0 in reply to Fernando Lopez
    Prodigy 170 points
    Sadly I was not logging during the learning cycle. I just started a log and I can run the cycle again overnight. I filled out the Q&A in accordance with my battery's tech specs. I'm not 100% sure on the chemID though; I didn't program it but I also was told that the default LiCoO2 setting should be fine.
  • 0 in reply to Tyler Barkin
    TI__Expert 8230 points
    Hello Tyler,

    For Impedance Track gauges, it is important to use the correct chemID file to ensure using the correct gauging behavior. We have an online tool that allows you to submit a discharge profile and see if you get a match to one of our exiting chemIDs on our database. Please search on ti.com for the GPCCHEM tool that details the proces to obtain a chemID.

    Thank you.
  • 0 in reply to Fernando Lopez
    Prodigy 170 points

    I submitted to Chem ID just now. I'll upload the log here as well. I just ran the cycle again at a lower discharge rate. It took a while but I'm met with the same results. I integrated the current during the charge and discharge cycles and I come up with a capacity that is equal to my batteries nominal capacity as reported by my vendor. I don't understand how even with an incorrect chemID that the gauge is so wildly inaccurate.

    PortalsBattery.zip

  • 0 in reply to Tyler Barkin
    Prodigy 170 points

    It worked this time. Seems like Chem ID fixed it. Thanks for your help