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BQ4050: Cell Balancing and COV Behavior in bq4050

Vinayak Sankar
Prodigy 50 points
Part Number: BQ4050

Tool/software:

Hello,

I am working with the bq4050 and observing some unexpected behavior related to cell balancing and Cell Over Voltage (COV) detection.

Issue Description:

  • Before charging, there was a 60–80 mV difference between cell voltages.
  • During charging, I noticed that the CB (Cell Balancing) bit is enabled, indicating that balancing is active.
  • However, one of the cells quickly reaches the overvoltage threshold (COV), causing the charger MOSFET to turn off and stop charging.
  • Once the recovery voltage is reached, charging resumes, but COV is triggered again shortly after, leading to repeated interruptions.

Questions:

  1. Is this the expected behavior of the bq4050 during cell balancing?
  2. Will this repeated COV triggering cause any long-term issues for the battery pack?
  3. How does the balancing function operate when COV is triggered? Does the gas gauge continue balancing, or does it stop until charging resumes?
  4. There is no detailed information on this behavior in the TRM or the cell balancing application note—is there any additional documentation or guidance available?

My battery has a charging voltage of 3.65V and the Overvoltage threshold is set to 3.75 voltage

cell balance threshold is 3450 mV

cell balance window is 100 mV

cell balance min is 40 mV

cell balance interval 20 s

Regards,

Vinayak

  • 0
    TI__Mastermind 26395 points

    Hello Vinayak, 

    It sounded like you are using different aged cells in the battery pack and/or cells that had different voltages when they were assembled. It is critical that whenever are using a battery gauge that you use cells that are coming from the same source/batch. From your issue description it does seem like your battery gauge acted as expected but there are registers you can change to disable feature and/or change how they operate. 

    1. Please refer to section 7.1 Introduction and it has the explanation of the cell balancing process along as the parameters that are associated with it

    2. There is a lot factors that go into but typically when a cell goes above its charge voltage than you accelerating the cell. This is why you shouldn't move the COV 

    3. This is more dependent on how your parameters are configured on your cell balance window and threshold along with OCV. But typically cell balancing will stop 

    4. The best way to see how cell balancing will act in different situation is to look at your parameter configuration for your cell balancing threshold features along with reviewing how different cell parameters are configured. The technical reference manual have explanation for each different parameter listed.

    Technical reference manual:
    https://www.ti.com/lit/ug/sluuaq3a/sluuaq3a.pdf?ts=1741978244573&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FBQ4050



    Thank you,
    Alan

  • 0 in reply to Alan Frias
    Prodigy 50 points

    Hello Alan,

    Thank you for your detailed response.

    Alan Frias said:
    registers you can change to disable feature and/or change how they operate

    Were you referring to the cell balancing configuration registers, or any other registers? I wanted to confirm if any additional configurations are required since my battery differs from the default settings of the BQ4050.

    Alan Frias said:
    This is why you shouldn't move the COV 

    As mentioned in my post, I am using a battery with a charging voltage of 3.65V, and its specification sheet lists an overvoltage threshold of 3.75V.

    Alan Frias said:
    But typically cell balancing will stop 

    That is evident from the reference manual. The cell balancing resumes when the cell voltage drops to the recovery voltage. However, the overvoltage threshold is reached quickly again, causing charging and cell balancing to stop very frequently. I was curious—if left for a long duration, would the cells eventually balance, even if the threshold is occasionally reached and temporarily halts the balancing process and start again?

    As you suggested, the issue might be due to the cells having different ages. What would be the tolerance level of the balancing feature in such a scenario?

  • +1 in reply to Vinayak Sankar
    TI__Mastermind 26395 points

    Hello Vinayak,

    -In terms of configuring your data flash memory there are critical parameters that need to be updated but the rest of the parameter are user discretion 
         Critical Parameters:
    Design Capacity, Design Voltage, Charge Term Taper Current, Discharge (Dsg) Current Threshold, Charge (Chg) Current Threshold, Quit Current and Term Voltage.

    -I would recommend updating your data flash parameters to revolve around the system charging at 3.65V and updating specifically the upper voltage parameter ranges.

    -Technically the cell would balance out eventually since the battery gauge has cell balancing features but the capacity (FCC) set pint doesn't improve since it lowered with the aging of the cell.

    -There is no real tolerance level that is acceptable than either being the lower the better. However I would recommend using different cell manufacture with guarantee new cells.

    Thank you,
    Alan

  • 0 in reply to Alan Frias
    Prodigy 50 points

    Hi Alan,


    Thank you for the response

    I have configured the parameters just like you mentioned.

    I shall try with new cells

    Thank You,

    Vinayak