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BQ24610: Blinking STAT1 LED on typical application BQ24610 design

Gregor Kalan
Prodigy 80 points
Part Number: BQ24610
Other Parts Discussed in Thread: BQ77905

Good day.

Im am having a problem with the typical application BQ24610 design. The system was working just fine charging the battery just fine then the charging stopped (not due to over temperature). Also the STAT 1 LED is blinking with a regular frequency. When the blink occurs the battery voltage jumps up 0.8 volt form 15.8V to 16.6V. Its not a clear jump at first the voltage rises about 0.1V then the rest. 

The system is using a BQ7790509PW battery protector, 4S battery and 20V input to charge.

IC setting are: 1.7A for max charging current, 0.3A for precharge, 3A max adapted current, TTC of 6.5h.

VREF is 3.3V, VFB is about 2V, VTS is 1.6V. If any other voltages need to be measured please tell me.

I also probed the charging mosfets and found that the device starts to charge then stops. So why does it stop?

The schematic is available bellow.

Thank you for your time and replay.

Best regards Gregor Schematic_Projekt-LED-Mitja_2020-06-06_19-23-36.pdf

  • 0
    TI__Mastermind 24075 points

    Hi Gregor,

      If there is too much impedance in the bath between the battery and where the charger senses the battery voltage, this can cause the charger to sense battery voltage + Ibat*Rimp. This causes the charger to detect fully charged termination, however once the termination current is removed, the sensed battery voltage goes back to true battery voltage. If the IR drop is more than the recharge threshold, it will cause the recharge comparator to trip and a new charge cycle is initiated. 

    You can disable termination to extend the battery run time, to observe if battery is being fully charged or not, as disabling termination stops the cycle. The STAT pin is most likely blinking according to cyclical

    1.reaching termination 2. charge stops 3. output voltage decays 4. Recharge threshold hit and new charge cycle initiated

  • 0 in reply to Kedar Manishankar
    Prodigy 80 points

    Hi Kedar,

    So I did some modding. First I connected a ground wire form the pack connection directly to the feedback resistor to reduce the impedance. That didn't work.

    Next thing I did is completely remove the BQ77905 and connected the battery pack directly to the charger. That "fixed" the issue and the battery got fully charged. But now the battery has no BMS to protect it.

    The question I have now is if the BQ77905 can even work together so battery being protected by BQ77905 and charged by BQ24610 through the low side protection of the BQ77905.

    Thank you for your time and replay.

    Best regards Gregor

  • 0 in reply to Gregor Kalan
    TI__Mastermind 24075 points

    Hi Gregor,

       Please create another post with BQ77905 in title. I am familiar with the BQ charge devices but not the gauge and protectors. If the post is tagged with part number BQ77905, then the expert on that part will be able to answer your question.

  • 0 in reply to Kedar Manishankar
    Prodigy 80 points

    Hi Kedar,

    I will make another post for the protector.

    But in your opinion, does the BQ24610 have to be connected directly to the battery and have no other sensing circuitry between the battery and the charger at any pol of the battery? 

    Else the charger will detect a charging fault.

    Best regards Gregor

  • 0 in reply to Gregor Kalan
    TI__Mastermind 24075 points

    Hi Gregor,

       The recharge threshold is a common feature for all battery charger IC. Having a protector IC with a charger IC is a common application scenario.

  • 0 in reply to Kedar Manishankar
    Prodigy 80 points

    Hi Kedar,

    So in my application the charger needs to be connected directly to the battery and NOT through the battery protector?

    Yes or no.

    Best regards Gregor

  • 0 in reply to Gregor Kalan
    TI__Mastermind 24075 points

    Hi Gregor,

        No, that is not what I was referring to above. Having the protector in between the charger IC and battery is intended application. Otherwise you would not have protection of the external battery protector.