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TCA Flag

George Mortimer
Expert 1205 points
Other Parts Discussed in Thread: BQ20Z90-V150, BQ20Z90

Dear community,

I am currently designing a battery and charger using the bq20Z90-V150 gas gauge chip in which I am using the TCA flag as a method of indicating Primary Charge Termination.  The customer has asked us to ensure that the charger works with a battery from an alternate source which uses the bq20z655 gas gauge.  The problem is that the TCA flag on the bq20z655  pack apparently sets and then immediately clears on Primary Charge Termination, so that the charger immediately resumes charging at the MCHG level until the charger reaches its timeout limit and signals a charge fault.  Looking at the .gg files, I cannot find any difference in the way the firmware handles charge termination.

Is there a difference between the bq20z90 and the bq20z655 in the way the controller handles TCA?  I have been told that TI has made some changes in the firmware of the bq20z655 to conform to smart charger specifications.

  • 0
    TI__Intellectual 2650 points

    Have you considered the CHGTERM bit setting and its effect on operation with your charger. This bit seems to control what TCA does at charge termination. Also would other settings like TCA Set , TCA Clear and maintenance current level etc need to be harmonized. e.g. does correct charger operation depend on certain settings being made a certain way so the pack responds appropriately to the charger and vice a versa?  

  • 0 in reply to Mike Ewer
    Expert 1205 points

    Mike,

    I have checked everything that I can think of - CHGTERM bit is the same on both (cleared), TCA Set and Clear % are the same (-1 and 95 respectively), Maintenance current =0.  As a note, when the customer set the maintenance current value up to about 50mA, he claims that the charger termination sequence works as we designed.

    Just as a sanity check, am I correct in assuming that without any other influence, setting the TCA Set % to -1 will set the TCA flag and it will remain in the set condition until RSOC drops to the TCA Clear % value?

  • 0 in reply to George Mortimer
    TI__Intellectual 2650 points

    George,

    Yes per TRM (below) with TCA set to -1,  TCA is set on primary charge termination and note the charging current is set to maintenance value and yes it's clearing seems to be determined by TCA Clear % value 

      

  • 0 in reply to Mike Ewer
    Expert 1205 points

    Mike,

    That part I understand, and yes, the bq20z90 behaves in that manner.  The problem is that the 20z655-based battery seems to be immediately clearing the TCA flag as soon as the charging current request drops to zero instead of waiting until the RSOC drops below the TCA Clear value of 95%.

  • 0 in reply to George Mortimer
    Expert 1205 points

    Mike,

    Some further information on the issue I am having.

    I tried resetting the Operational Configuration bytes to the same values as the bq20z90 circuit that works correctly with the charger firmware. Changes were as follows:

    Operation Cfg A from AE28 to 1E29

    Operation Cfg B from 2557 to 6C48

    Operation Cfg C from 003D to 0001

    Non-Removable Cfg from 3007 to 0000

    What happened in this instance was that the charger still recorder a timeout fault; however the TCA did remain set.  The problem was that other faults showed up (which is probably what prevented a proper charge termination), and when the pack was subsequently discharged, the TCA did not clear when RSOC dropped below 95%.  I fully discharged the battery until TDA and FD came on, but the TCA still did not clear.  I had to reset the battery (Mfr Cmd 0041) to get the TCA to clear.

    Would it be beneficial for me to load the entire bq20z90 .gg file (with modifications for the multiple temp sets in the bq20z655) into the problem battery and see what happens? Or is there anything else that I might try to isolate this odd performance of the TCA?

  • 0 in reply to George Mortimer
    Expert 1205 points

    Mike and/or Doug,

    I tried the modification I proposed to the .gg file in the above message, and got the same result as previously (i.e. TCA did not set or set and immediately cleared).

    I was browsing through some information one of our former engineers had acquired on the SBS specification and found the following notes regarding TCA vs. FC:

    TERMINATE_CHARGE_ALARM (BIT 14)

    - Set when charging should be stopped but the Smart Battery may not yet be in a Fully Charged state.

    - Charging is effectively ‘suspended,’ usually temporarily.

    - Cleared when the Smart Battery detects that it is no longer being charged.

    FULLY_CHARGED (BIT 5)

    - Set when the Smart Battery determines it has reached a full charge point.

    - Cleared when the battery may want to be charged again, which is chemistry and manufacturer specific.

    Is this a correct exposition of what the TCA is supposed to do, and is this the difference between the bq20z655 and the bq20z90 that the bq20z655 is more fully SBS-compliant than the bq20z90?