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BQ24735: ACOK briefly goes low when approaching UVLO

Alex Semenov
Prodigy 10 points
Part Number: BQ24735
Other Parts Discussed in Thread: BQ24780S

Hello there,

I am trying to adjust valid input voltage range to be 11.9V-15.1V. The values of resistors on voltage divider to ACDET are 470k and 121k. I'm testing with the power supply, voltage set to 12V. What I observe is that output voltage from a charge controller is constant but ACOK toggle low every ~50ms for duration of ~20us. This is sufficient to indicate to a microcontroller that something is wrong with a charger and put it in a panic mode. The issue with ACOK goes away when I adjust input voltage to ~13V (input current 2.6A, current limit set to 2.9A). Why is this happening? Can I fix this in hardware somehow? I would like to use both 12V and 15V power supplies with this charge controller. Ideally, I would like to have even wider input range, but I understand it is not possible since input to ACDET has to be between 2.4V-3.15V. Something to note.. datasheet states that AC adapter operating range is 4.5V-24V which is deceiving. I don't see what resistor values on voltage divider can give this input voltage range.  

  • 0
    TI__Genius 11385 points

    Hi Alex,

    There are a couple options you can look into:

    1. You can have a FET and resistor in parallel to the current bottom resistor to change the total effective resistance:



    I have seen customers do this to feedback path of other DC-DC converters (not BQ24735).

    2. Want to look into BQ24780S? Adapter overvoltage is handled by VCC pin for this part. I would recommend testing an EVM first to ensure it satisfy your needs.

    Thanks and I hope this helps,

    Peng

    *Please press "This Resolved My Issue" on the thread if my answer is satisfactory

  • 0 in reply to Pengzhao Zhu
    Prodigy 10 points

    this would require microcontroller on the board to be power from something else in order to turn on that FET. All power in my circuit comes through BQ24735

  • 0 in reply to Alex Semenov
    TI__Genius 11385 points

    Hi Alex,

    The battery is available to power your system. In addition, you can look into BQ24780S.

    Ultimately, this is a decision of the system designer.

    Thanks and I hope this helps,

    Peng

    *Please press "This Resolved My Issue" on the thread if my answer is satisfactory