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BQ40Z50-R1: Keeping TCA bit set even after charging has stopped

Zahid Shafi
Prodigy 70 points
Part Number: BQ40Z50-R1
Other Parts Discussed in Thread: BQ20Z70, , BQ40Z50, BQ20Z80

Hi,

For one of our customers, we have re-designed a long running legacy battery product from a BQ20z70 to a BQ40z50-R1.

Due to the backward compatibility required between the old and new battery packs as far as Battery Status registers are concerned, the TCA bit in Battery Status needs to remain set even after the charging has stopped and the average current is zero. 

In the BQ20z70, this is possible and the TCA bit remains set, along with the FC bit. However, I have not been able to achieve this with the BQ40z50-R1, as the TCA bit changes to zero once the average current drops to 0.

I have tried all the options within SOC Flag Config A  and SOC Flag Config B. 

Please can you assist?  

BTW, I did see a 5 year old thread on the forum where Onyx implied to a query that in the BQ40z50, the TCA bit will always revert back to 0 soon after being set, but it was not clear to me if this was to a particular GG file or it is a change designed into the BQ40z50 over the BQ20zXX fuel gauges.

Thanks and regards,

Zahid

  • 0
    TI__Guru** 102375 points

    Hello Zahid,

    I don't believe the TDA function is the same in the newer gauges like the BQ40Z50, TDA will be set by multiple factors:

    You should be able to set the FD to reflect the same voltage value as the BQ20Z80. Just make sure the correct bits are set to use the voltage based thresholds:

    Sincerely,

    Wyatt Keller

  • 0
    Prodigy 70 points

    Hello Wyatt,

    Thank you for your response. 

    You have made reference to the TDA function as opposed to the TCA function / Bit which I was asking about. We need this TCA bit to be set beyond the point the charger is removed and the average current reaches zero, which it does do in the BQ20z70.

    I have tried all the settings and permutations I could see that have an effect on the TCA bit, but it always reverts back to zero once the average current reaches zero.

    Therefore, it is a definitive question to TI. Has this bit behaviour changed from the BQ20z70 to the BQ40z50? Will it always be that the TCA = 0 after the charger has been removed and the average current reaches zero?

    Thank you.

  • 0 in reply to Zahid Shafi
    TI__Guru** 102375 points

    Hello Zahid,

    Both flags have very similar functionalities. I believe the behavior of that flag has been modified over time, it is not 100% matched with the legacy gauges operation. All flag operations are defined in the TRMs for each respective gauge.

    We would need to know what functions you are using that sets the TCA in order to check what would clear the flag since there are multiple reasons for it to clear. Section 4.8 Terminate Charge and Discharge Alarms describes what will set TCA.

    Sincerely,

    Wyatt Keller 

  • 0 in reply to Wyatt Keller
    Prodigy 70 points

    Hello Wyatt,

    Yes, there are a number of reasons that will set a TCA in a BQ40z50 and that is fine.

    The question is that when a full charge sets the FC bit and the TCA bit, is there a way to set the TCA clear by a % decrease in capacity or set a timer etc? 

    The BQ20z70 actually has a TCA CLEAR register and this is what our customer has been using to manage their charger and now with the upgrade to the BQ40z50R1, their existing chargers in the field will not function correctly.

    Thank you.

     

  • 0 in reply to Zahid Shafi
    TI__Genius 11750 points

    Hello Zahid,

    Wyatt isn't here today, but I think I see the problem here. You can have TCA go high when TC is high and the gauge is in charge mode. When the current drops to zero, it is leaving charge mode and clearing the condition. So while you can have TC set and reset based on voltage/RSOC, the second condition seems to be causing issues. This seems to be the major difference between the new and old devices.

    Is it possible to have the charger go based on the FC alarm rather than TCA? The FC does not include the charge condition and should be settable based on RSOC like you describe. This seems to be the best solution to me, but I don't know if your charger can use this alarm. 

    Otherwise, the only work around I can see would be to adjust some of the safety alerts to set when you terminate charge, but that's not really the preferred solution. Let me know if the FC alarm is not usable, and I can look more into possible workarounds. Do you have a host MCU in your system?

    Thanks,

    Alex M.

  • 0 in reply to Alexander Mazany
    Prodigy 70 points

    Hello Alexander,

    Thank you for stepping into this conversation in Wyatt's absence.

    You have understood our problem. The FC alarm alone is not usable as the existing gang charger firmware was designed by our customer many years ago to use the TCA  bit AND the FC bit to inform their MCU to disable the charger and change the indicator LED to green. Because they have so many such chargers out in the field and not able to be re-programmed on site, they would have to be re-called for re-programming in order to use the new BQ40z50 version of the battery pack.

    I can understand that adding a new register for TCA clear % would be very difficult for TI to implement, but would it be possible to have a timer set for TCA clear, if set by charging only and as long as the FC bit is set? We would only use this modified SREC firmware for this battery pack and install a BQZ file if required for BQ Studio.

    Looking forward to your response.

    Thanks,

    Zahid

  • 0 in reply to Zahid Shafi
    TI__Guru** 102375 points

    Hello Zahid,

    You would need to contact your TI representative to get any custom made firmware or changes to existing firmware since it must be very high volumes for it to be justified by the business team.

    Sincerely,

    Wyatt Keller 

  • 0 in reply to Wyatt Keller
    Prodigy 70 points

    Hello Wyatt,

    Please can you let me know who would be the person at this moment for me to discuss with off line on this topic? My TI connection is actually with TI, Dallas but not sure who at present is the Product Manager for the BQ40z50. My previous contact moved on to another TI division.

    Thank you.

  • 0 in reply to Zahid Shafi
    TI__Guru** 102375 points

    Hello Zahid,

    I have sent you a friend request on the forum.

    Sincerely,

    Wyatt Keller