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BQ20Z45 FC flag not set when Relative State of Charge = 100%

Doug Young
Intellectual 315 points
Other Parts Discussed in Thread: BQ20Z45

Hi,

I have a 4 cell pack design using the BQ20Z45.  At the moment I am running tests using cells that have been stored for over 1 year and are no longer evenly matched in charge.  Due to the cell mismatch, charge is terminated by a COV safety flag but relative capacity is reported as 100%, however the FC flag is not set.

I would very much like the FC flag to be set while an OCV QMAX update is made so the Gas Gauging Update Status will transition to 0x0E (currenty it is 0x06), thus enabling cell balancing during the next charge cycle.

Without cell balancing enabled the pack is still usable but I expect its relative capacity will increase as the cells balance out.  The production volume and use scenario for this product make it likely that cells could be sitting on the shelf for 6 months or more before they are used in a pack.

Do you know why the FC flag is not being set?

Are there settings that I can modify to allow the flag to be set under these conditions?

Sincerely,

Doug

  • 0
    TI__Guru 73830 points

    Are you sure that the pack is reaching charge termination? This could be the reason that the FC flag is not getting set. You could force Update Status to 0E to enable balancing, but you run the risk that cell will get further imbalanced, if Qmax is not accurate.

  • 0 in reply to ThomasCosby
    Intellectual 315 points

    In the attached log spreadsheet file the pack is charging and is terminated at 90% RSOC by COV.  The pack does not taper current sufficiently to meet the conditions for primary charge termination as defined in the BQ20z4x technical reference (SLUU313A, section 2.5.7).  

    • Is the FC flag only set when the conditions for primary charge termination as defined in section 2.5.7 of technical reference are met?

    The RSOC remains at 90% as the cell voltage dissipates but jumps to 100% when the PRES# pin is pulled low and a load is placed on the pack (last entry of the log file).  

    • Is RSOC supposed to jump to 100% when the pack switches from charge to discharge mode and is there a setting to prevent this from happening?

    Of note, the RSOCL bit (configuration register C) is set and relative state of charge is 100%.  Also per section 2.5.7, if the RSOCL bit is set, relative state of charge will only report 100% after primary charge termination occurs.  

    Doug

    GGUpdateStatus06_chg1.xls

  • 0 in reply to Doug Young
    TI__Guru 73830 points

    Doug

    The gauge will force the RM to FCC at charge termination. I do not have your gg file, so I am not sure that it met the taper current criteria. The gauge will run a simulation at the start of discharge. I am not sure which ChemID you are using, so I am not sure whether the cell voltages are at a level where the pack would be consider to be fully charged. I assume that they are, since the capacities were upgraded.

    Tom