• State
  • Locked Locked
  • Replies 2 replies
  • Subscribers 63 subscribers
  • Views 302 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

FC bit clears during 2 hr Charge Relaxation phase

chirag patel
Prodigy 65 points
Other Parts Discussed in Thread: BQ27500

I'm trying to do a learn cycle with BQ27500 evm. After the Charge reaches 100% (FC bit gets Set), during the 2 hr relaxation phase the Voltage drops down to 4.17V and the FC bit clears and the SOC shows < 98%! This causes the Learn Cycle to Fail. I don't have any load on the battery. I calibrated the current correctly. I do know that the battery will self discharge after Charger is disabled and it won't stay at 4.2V. I set the design capacity at 350mAHr and Taper current to 20mA. I wait until the FC bit gets Set. I also noticed that the FC bit gets set sometimes at 35mA (instead of 20mA). I also identified correct chemistry using Chemistry cycling and Mathcad.

Need help from gas gauge experts since i've given up and currently scratching my head. I have used BQ27505 (newer version of gas gauge) and never had this issue. 

  • 0
    TI__Genius 14985 points

    You can try to charge to a fuller state by continuing to charge until taper current reaches a lower level.

    What is the capacity of your battery?  20mA taper current is pretty small unless your battery is very small. 

    Your chemID may also not be a good match which could explain why it drops to 97% during relaxation after charge.

  • 0 in reply to dMax
    Prodigy 65 points

    Hi, the capacity is 350mAHr and the manufacture specs 20mA taper for full charge. Previously i was using a different chemistry id which is why it didn't work. Then i used default chemistry and the FC bit didn 't clear prematurely. So, as you mentioned, it could be related to the chemistry id.

    After i successfully created the golden image using default chemisty, i flashed this image into a different unit but using physically different battery (same capacity/model)  when i try to do a full charge, the FC bit gets set at 50mA instead of 20mA. Any clue why this could be happening though?