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BQ24780S: insert power adapter, bq24780s IC will ask for current more than 5A

Yang Nathan
Prodigy 20 points
Part Number: BQ24780S

We use bq24780s to charge 3-cell battery, we set input current to 3A, charge current to 2A, charge voltage to 12V.

But when we insert power adaptor, the IC will ask more than 5A current from power adaptor (which is 19V/3A), that cause adaptor protect self.

what is possible wrong?

with best regards and thanks.

Nathan Yang

  • 0
    TI__Guru 56650 points
    Nathan,

    Do you use an EVM or your board?
    Do you have a system load?
    Do you enable charge when you see "IC will ask more than 5A" ?
    "IC will ask more than 5A?" Where do you measure the 5A? What is the Vacp-acn?
  • 0 in reply to Wang5577
    Prodigy 20 points

    Hi Wang:

    Do you use an EVM or your board? 

    Nathan -> Our own board.

    Do you have a system load?

    Nathan -> We connected 3-cell battery.


    Do you enable charge when you see "IC will ask more than 5A" ?

    Nathan -> We don't enable charge, but no matter enable or disable(by register 12H), once plug in power adaptor, the charge circuit will immediately request more than 5A current from power adaptor.


    "IC will ask more than 5A?" Where do you measure the 5A? What is the Vacp-acn?

    Nathan -> We measure with DC power supply. We are using same design as reference design.

  • 0 in reply to Yang Nathan
    TI__Guru 56650 points

    Nathan,

    We have to step by step to find out the root cause.
    1. Pull ILIM pin low and measure the input current. This step makes sure the bias circuit no problem.
    2. Enable the Learn function and release the ILIM pin and measure input current. This step makes sure the charge pump circuit not short.
    3. Release the ILIM pin to measure the inductor current; Vin and Vbat. This step checks the short is happened before inductor or after inductor.
    4. Compare your schematic and layout with the EVM again to list the key differences.
    5. Compare waveforms between your board and the EVM