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TPS63020 - PG Leakage Current

Robert Blake
Prodigy 160 points
Other Parts Discussed in Thread: TPS63020

Hi,

I have a design using the TPS63020 to generate 5V from a single-cell Li-Po battery (3.0 - 4.2V input).  However, I'm running into an issue where the PG output seems to be sinking more leakage current than specified in the datasheet - around 0.85uA, which is nearly an order of magnitude greater than the stated maximum. I arrived at this current value based on the voltage present on 5V_PWR_GOOD when the part is enabled and nothing is connected to the PG output besides the pullup resistor.

I could get around this problem simply by reducing the value of the pullup resistor, but I'd rather figure out why the part isn't meeting its specification.  I have attached a schematic and the layout I am using.  Note that the 5V_EN, 5V_P\S\, and 5V_PWR_GOOD ports are all connected to a 3.3V microcontroller.  However I have verified that this excessive leakage occurs even when the microcontroller is not populated and the enable pin is directly connected to BATT+.

Also worth noting is that I have used the TPS63020 before, in an identical configuration, on another product without any issue (using a full 1Mohm pullup).

Does anyone have any idea why I might be seeing this?  I'm happy to provide any more information if necessary.

Thanks,
Bob

  • 0
    TI__Expert 7110 points

    You are connecting the PG to an external 3.3V rail via the resistor R18, right?

    Do you see this behavior when the 3.3V rail is present or when the rail is '0' or in either cases?

  • 0
    TI__Guru*** 147810 points

    Thanks for sharing your schematic and layout.

    I'll note that anything you use to measure the voltage or current there will consume current itself.  i.e. a multimeter or scope probe has an input impedance which draws some current.  You might measure the voltage with a multimeter, which is itself in series with a current meter to see how much this leakage is.  You might also share the method by which you computed the leakage current into the PG pin.

  • 0 in reply to Chris Glaser
    Prodigy 160 points

    Mr. Glaser, thank you so much!  You nailed it.  I was neglecting to consider the leakage through my probe, which, because of the high impedance of this circuit, was responsible for the bulk of the voltage drop I was seeing.  Using my bench multimeter with its inputs set to Hi-Z (>10 Gohm), PG is pulled up to about 3.29V - well within the range that I would expect.

    Thanks again to both of you for your help.

    -Bob