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BQ27520-G4: Issue with learning cycle not completing successfully

MM
Intellectual 380 points
Part Number: BQ27520-G4
Other Parts Discussed in Thread: GPCCHEM, BQSTUDIO

Dear Sirs and Madams,

We are considering BQ27520-G4.

The specifications of the batteries used in operation verification are 3.7V, 1500mAh, and 5.7Wh.

Successfully got the ID from GPCCHEM of TI website and am using ChemID : 0321.

Initially, we used CHEM ID : 1200, which is the best reported by GCPCHEM, but RUP_DIS becomes 'H' during the learning cycle test, so we use CHEM ID :0321.

By adopting CHEM ID 0321, RUP_DIS can maintain 'L'.

I think VOK is also trending normally.

However, even after finishing the learning cycle, the Update Status in the data memory remains 0x00 and does not become 0x02.

I have investigated E2E, TRM and "Achieving The Successful Learning Cycle" variously, but I have not been able to identify whether it is a problem.

The settings for each current are as follows : 

 -  Taper current : 150mA (=C/10)

 -  Dsg current threshold : 90mA

 -  Chg current threshold : 110mA

 -  Quit current : 75mA (=C/20)

It meets the following conditions:

 -  “Dsg current > Quit current”

 -  “Taper current > Chg current > Quit current”

Do you know what is the reason why Update Status remains 0x00 and does not change to 0x02?

Only "Cycle Count" and "Cell 0 V at Chg term" of Gas Gauging and "CC Offset" of Calibration are updated.

/* Achieving The Successful Learning Cycle document URL */

https://www.ti.com/jp/lit/an/slua903/slua903.pdf?ts=1686040068138&ref_url=https%253A%252F%252Fwww.ti.com%252Fsitesearch%252Fja-jp%252Fdocs%252Funiversalsearch.tsp%253FlangPref%253Dja-JP%2526searchTerm%253DSLUA903%2526nr%253D208

Regards,

MM

  • 0
    TI__Genius 16746 points

    Hello MM,

    Can you please share your gg file and also a BQStudio log file, so I can help further debug your problem.

    Did you send the "IT_ENABLE" before starting the learning cycle process. Usually, whenever this command is sent,
    "Update Status" should automatically change from 0 to 4.

    Sincerely,
    Nick Richards

  • 0 in reply to Nick Richards
    Intellectual 380 points

    Hi Nick,

    I appreciate your correspondence.

    I am attaching the gg file, the .log file, .err file.

    As per the procedure, "IT_ENABLE 0x21" and "RESET 0x41" commands are issued before acquiring log data.

    > "Update Status" should automatically change from 0 to 4.

    The Update Status of BQ27520-G4 is defined from 0x00 to 0x03 in TRM, so it remains at 0x00.

    LogAndGgfiles.zip

    The discharge current is about C/7, the charge current is about C/2, and the termination voltage is 3000mV.

    [C/5 Discharge] => [Relax Time 5H]=>[C/2 Charge]=>[Relax Time 2H]=>[C/5 Discharge]=>[Relax Time 5H]

    I'm confirming for the .log file, but STATUS and FLAGS seem to be fine.

    I am concerned that "Undefined FCC" is issued to the error file (.err) every time.

    However, even if I confirm for the log data for the time when this error is issued, it is doubtful that it is issued at a time that isn't  related to full charging.

    Regards,

    MM

  • 0 in reply to MM
    TI__Genius 16746 points

    Hello MM,

    What Chemistry of battery are you using, and is 3V the termination voltage specified on the datasheet? For learning
    cycle purposes, we want to discharge the battery as close to the specified termination voltage on the datasheet.

    For the future, please also log the current in BQStudio as this is a important piece of information for debugging.

    Sincerely,
    Nick Richards

  • 0 in reply to Nick Richards
    Intellectual 380 points

    Hi Nick,

    From your advice, I set the Termination Voltage to 3200mV instead of 3000mV and got the new ChemID 1265 from GPCCHEM.

    Using that ChemID 1265 and setting the end voltage to 3200mV and checking the learning cycle, I was able to confirm that the Update Status changed from 0x00 to 0x02 and that the Ra Tables were also updated.

    I understood that it is difficult to use this battery to the limit of the lower limit.

    Even if "Control Status", "Flags" and”Operation Status”” respond normally, are there cases where the learning cycle cannot be completed correctly?

    Regards,

    MM

  • 0 in reply to MM
    TI__Genius 16746 points

    Hello MM,

    There are many cases for why learning cycle cannot be completed correctly. For instance, not using
    the correct ChemID for your battery, not reaching valid charge termination, and simply not having
    a long enough rest period after charge and discharge, just to name a few.

    Sincerely,
    Nick Richards

  • 0 in reply to Nick Richards
    Intellectual 380 points

    Nick-san,

    It' make sense.

    In the case of this battery, it turned out that it was difficult to use it to the very lowest limit even if the matching CHEM ID was obtained with GPCCHEM.

    We would consider using a termination voltage of 3200mV or 3100mV instead of 3000mV.

    Your advice was very helpful.

    Regards,

    MM

  • +1 in reply to MM
    TI__Genius 16746 points

    Hello MM,

    Glad I was able to help!

    Yes, termination voltage can be set to a value that is applicable to your system after completing the
    learning cycle. 

    Sincerely,
    Nick Richards