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Original question:

BQ24610: BQ24610: Audible noise

BQ24610: Charging termination logic

M K
Prodigy 50 points
Part Number: BQ24610

Tool/software:

Hi all!

I've been struggling with getting BQ24610 to work in my product. One of few problems I encountered is this:

I use BQ24610 to charge 6xLiIon battery pack. I use power adapter fine-adjusted to exactly 26.5V, and after back-power preventing schottky diode, BQ charger 'sees' 26.2VDC.

With resistor dividers I set V_BAT=24.44V, I_CHARGE=1.05A, I_TERM=0.28A.

Right now I'm looking at my PCB, and I measure battery pack current = 83mA, and battery pack voltage = 24.93V. So if I correctly understand datasheet p. "9.3.5 Charge Termination, Recharge, and Safety Timer":

When VTTC is valid, termination is detected while the voltage on the VFB pin is higher than the VRECH threshold AND the charge current is less than the ITERM threshold.

VRECH for my divider is 23.85V (50mV drop on VFB). So what is going on? Both conditions are met. Charging should be terminated, but is not. When I leave it for few more hours, a TTC timer will kick in and indeed terminate the charge, and signal it properly (STAT1 = STAT2 = off). I have TTC timer set for 4:40h. Is there something I'm missing?

One might say: maybe your VFB resistor divider is not accurate enough (1% resistors), and you are not really above VRECHG threshold. Ok, if so, then why did BQ decided to end the fastcharge current regulation and drop the current from full charge 1.05A down to tens of mA? 

Anyone has idea why this might happen? Or is it just me not understanding datasheet?

Cheers,

Mateusz

  • 0
    TI__Mastermind 33171 points

    Hello Mateusz,

    What is the measured voltage on the TCC pin when charger is suppose to terminate?

    Best Regards,

    Christian.

  • 0
    Prodigy 50 points

    Hi!

    Voltage on TCC pin is 1.26V with conditions that I described earlier.

  • 0 in reply to M K
    TI__Mastermind 33171 points

    Hello Mateusz,

    Yes, The charger should be terminated.

    What is the voltage on VFB?

    In your schematic it shows ITERM as 150mA but in your description its says 280mA. which one is correct?

    What is the charging current when the device disables charging during timeout?

    Best Regards,

    Christian.

  • 0
    Prodigy 50 points

    Hi Christian!

    Yes, I changed the ITERM recently and forgot to update schematics. I wanted the charging process to end earlier, because of all the problems with charging with low current (my other post about audible noise). So for today, it is set to 280mA. But in future, it may be set to even higher current. That is because audible noise problems are the worse with lowest currents.

    When BQ disables charging after timeout, current actually drops to ~0A.

    The voltage on VFB in mentioned situation is 2.046V. This is lower than threshold VRECH level which is 2.05V. Additionally, VRECH has a min/typical/max specified, so may vary from unit to unit. In my case it would be (min/typ/max): 32.68/23.85/24.03V. Ok, now I see why the charging is not terminated - one of conditions is not met.

    Question remains: why is BQ lowering charging current before reaching VRECH?

    Best regards,

    Mateusz

  • 0 in reply to M K
    TI__Mastermind 33171 points

    Hello Mateusz,

    M K said:
    The voltage on VFB in mentioned situation is 2.046V.

    Are you measuring at the  IC? The charge current will slightly start to reduce as the VFB reaches 2.1V. What does the current reduce to? what is the current before the timer disables charging?

    Best Regards,

    Christian.

  • 0
    Prodigy 50 points

    Hello Christian,

    Thanks for being persistent with your support.

    I measure VFB as close as possible to IC, at resistor pad of resistor divider, ~6mm from actual IC pad.

    In units that have this problem (~3 out of 6) I've seen current droped to 80-100mA, and one time it even reached 10mA, and still charging.

  • 0 in reply to M K
    TI__Mastermind 33171 points

    Hello Mateusz,

    M K said:
    In units that have this problem (~3 out of 6) I've seen current droped to 80-100mA, and one time it even reached 10mA, and still charging.

    Do you still see this if you remove the system load?

    Best Regards,

    Christian.

  • 0
    Prodigy 50 points

    For anyone interesed: there is a solution to this problem described in different thread: here.