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BQ27546-G1: SOC decrease after few hours charging up - devices still in the charger not connected to load

Son Nguyen20
Prodigy 70 points
Part Number: BQ27546-G1
Other Parts Discussed in Thread: BQSTUDIO

Hi, I am currently using BQ27546 and integrated into device with small battery 165mAh 3.7V (Charging voltage 4.2V). I have update the data flash with Q_cell_max  = 165, CC Gain is set at 19 mOhm. The other setting is set as default in BQ27546 technical reference document http://www.ti.com/lit/ug/sluub74/sluub74.pdf

  • 0
    TI__Intellectual 1840 points
    Hi Son,

    Have you programmed a suitable CHEM_ID, followed by a successful learning cycle ? You will get erroneous readings and results unless you have a good CHEM_ID match programmed followed by a successful learning cycle.

    Please look at these links if you haven't performed these two actions:

    For CHEM_ID selection: www.ti.com/.../slva725.pdf

    For performing a successful learning cycle: www.ti.com/.../slua597.pdf

    Hope this helps,

    Nabil
  • 0 in reply to Nabil M
    Prodigy 70 points

    Thanks Nabil.

    Unfortunately, i did not change the Chem_ID. It is currently read default as 0×354 in hex. Where can i find the table of Chem_ID so i can find one that possibly matched with my current battery ?

    Also, for charge termination, there are taper current, taper voltage, min taper capacity, termination voltage, termination current, threshhold etc. They are all at default value. Do i need to change them all ?

    My device is currently charge up to 99-100% then the charger cut off charger current. I still keep it in the charger for few hours the SOC drop back to 90% and stay stable at that point. Voltage i read out from cell is 4.184V which i think it should be capable to read as 100%. Battery is new.

  • 0 in reply to Nabil M
    TI__Mastermind 48931 points

    Hi, Nabil,

      Thanks a lot for the information you sent to customer! 

    Hi, Son,

      To figure out the issue you reported, would you please share us a log file so we may re-produce the behavior? Also schematics to show us how the battery charged and current measured is a great help as well.

    Thanks!

    Phil

  • 0 in reply to Son Nguyen20
    TI__Mastermind 48931 points
    Hi Son,
    For CHEM_ID selection, please follow the guide linked by Nabil.
    Yes, according to your battery capacity, you have to change some the default values if they're not in the type of %; for example, if use 1C charging, the charging current shall be 165mA, and C/10 taper current shall be 16.5mA. Setting the termination current lower can make SOC closer to 100% and keep the level after a few hours relaxing.
    Please let's know if you need help or have further questions!
    Thanks!
    Phil
  • 0 in reply to Phil Yi
    Prodigy 70 points

    Hi Phil,

    Thanks for your reply. However, changing CHEM_ID has no effect on what is programmed on to the gauge. BQ27546 Technical reference page 91.

    I don't think change CHEM_ID in data flash will help to get it right SOC.

    I am not very clear at the beginning that I didn't use BQStudio or even have EV2300 I2C interface. I only communicate with gauge device using raw I2C from serial terminal. I can access to data flash to change the parameter. I will gave you the log files which contain Time, SOC, Current, Voltage and Temperature as soon as I can.

  • 0 in reply to Son Nguyen20
    TI__Mastermind 48931 points

    Hi, Son,

      Please check datasheet page 26 about right way to update Chem_ID; better matched Chem_ID gives higher gauge accuracy. 

      Yes, please use BQStudio and EV2300 to get log files and also you can export a GG file which can help us understanding more with your setup. 

      Please let's know if you have further questions.

      Thanks!

      Phil

  • 0 in reply to Phil Yi
    Prodigy 70 points

    Hi Phil,

    I figure out that I didn't update the CC delta before. Today,  I updated on both CC Gain and CC delta = 19mOhm and try again charging up and leave device in the charger for 5.7 hours (files attached).. It is now read 99% for more than 5 hours. So what i understand is CC Gain and CC delta: one affects AverageCurrent and one affects Remaining Capacity (in this case directly affects SOC).

    About the CHEM_ID, if i understand correctly, each of CHEM_ID is attached with Ra Table (Chemistry resistance table) in BQstudio. So when you change the CHEM_ID in BQstudio, the Ra Table will be update into data flash of the gauge, which helps to track the cell battery accurately.

    The fuel gauge is itself only stored default Ra table.

    By default, the Ra table in the gauge gave default values in the data flash that may or may not track your battery accurately.

    Yes i bought EV2300 and will use BQstudio to help me to get the correct setting for my gauge.

    battery_test.txt

    battery_test_results.zip

  • 0 in reply to Son Nguyen20
    TI__Mastermind 48931 points
    Hi, Son,
    You did great job! Yes, not only resistance tables but also open-circuit voltage will be updated by matched CHEM_ID update.
    Please let's know if you have further questions; or, If all your questions answered, please help to mark it answered to close the case.

    Thanks a lot!
    Phil