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BQ24618: can only charge up to 12.6V for 3-cell(4.35V*3)

Harson
Expert 3700 points
Part Number: BQ24618
Other Parts Discussed in Thread: BQ24600

Hi, Team

My customer Autel is using BQ24618 to charge 3-cell battery, each cell is 4.35V.

So they adjust the feedback resistor to 22.1K & 4.22K, which can set the VBAT charge up to 13.05V.

But the test result shows the charging will only arrive at 12.6V, which seems only accept 4.2V/Cell.

Charging current is about 4A.

Can you please double check if BQ24618 support cell voltage >4.2V?

I find BQ24600 which looks maybe support 4.35V, is it the right choice?

  • 0
    TI__Genius 16175 points
    Harson,
    Based on datasheet's description, BQ24618 should support different battery voltage level. Can you help to measure VFB pin voltage to check is the voltage level? is it 2.1V or lower?
    Thanks
  • 0 in reply to Paul Yeh
    TI__Expert 3700 points

    Hi, Paul

    I have asked customer verify the value of the VFB divider, there is no problem with them.

    Then the voltage should be 2.02V.

    I will update you the voltage when VBAT is 12.6V after measured by multimeter.

    From our design VFB = 4.22/(4.22+22.1) * 13.05 = 2.09V.

    From the caculation tools of ti web:

    VCELL for BQ24618 is not adjustable, but with fixed value. In BQ24600, it is able to change to 4.35V.

    This is why I'm confused about the VFB of BQ24618.

  • 0 in reply to Harson
    TI__Genius 16175 points

    Yes, it is strange for me. So I will ask Joel for advise.

    Thanks

  • 0 in reply to Paul Yeh
    TI__Expert 3700 points
    Hi, Paul
    This issue has figured out that the VIN is not high enough for charging to 13.05V.
    Customer's adapter is only ~13.1V. When it is increased higher, the VBAT can charge to 13.05V.
    Thanks for helping with me.