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PMP9780: How to change the output current of the charge pump?

Part Number: PMP9780
Other Parts Discussed in Thread: TPS65131

Hi Expert,

My customer is evaluating this reference design PMP9780. They want to get a bigger output current of the charge pump circuit (max 15mA).

Do you have any suggestion about this. Could you please provide any equation for parameter calculation?

Thanks!

Best Regards,

Wilson

  • Hi Wilson,

    The current in the charge pump is limited due to internal transistors in the IC, so there is no way to increase it.

    Thanks

    Robert

  • Hi Robert,

    I think TPS65131 can only change the ON time and OFF time of the charge pump.

    Could you please explain, which internal transistor influence the current limit?

    Best regards,

    Wilson

  • Hi Wilson,

    Sorry for my confusion on your original question.

    The charge pump current is limited by the amount of power that the boost rail can provide (the 6.3V rail).

    The IC can support up to 2A switch current, so with 3.3V input and 6.3V output that means a max current of ~700mA

    The charge pump triples the output voltage, so that mean 1/3 of the current. 

    In addition to that, the capacitors charging and discharging will have some ripple, that will change based on load current.

    In general the charge pump will be able to support up to 50mA with no issues.

    Hopefully this helps.

    Thanks,

    Robert

  • Hi Robert,

    Thanks for your answer.

    Actually, in this reference design, the spec states that the max current is 10mA(As shown in the picture). And my customer proved this value in the real board. If the current is larger, the output voltage will drop down.

    So is there any way to increase the output current?

    I already suggested the customer to increase the value of flying capacitors but still can not supply bigger currents. Do you have any comments for your side?

    If we can help customer increase the current, they will buy in our solution.

    Best regards

    Wilson

  • Hi Wilson,

    I studied the circuit more.  The only thing I can think of is that the loading on the 6.3V rail is not enough to maintain the charge pump.

    When the customer tried to load the +16V rail, what was the load on the 6.3V rail?  If there is not enough load, then the voltage will start to sag.

    I can't think of any other reason. We may need to get someone from the product line involved.

    Thanks,

    Robert