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TPS22953: TPS22953 EN pin leakage current is high leading to shutdown with large (100k+) resistor divider values

Patrick Caputo
Prodigy 10 points
Part Number: TPS22953

I am using TI part TPS22953DQCR.
The EN pin is supposed to have <0.1uA of leakage current.
I thought that meant I could safely use a 357k (high side) and 100k (low side) resistor divider network on the EN pin.
I learned that those values don't work well and cause the load switch to turn off frequently.
I don't have good guidance from the datasheet for the max resistor values I can safely use.

We did further testing and the EN pin leakage current appears to be ~1 to 3uA with Vbias of ~3.2V.

Below is our circuit.  The BATTERY_RAW net is supplied by a single cell li-ion battery pack.

R41 is depopulated.  R349 is depopulated.  We have the issue with or without C88 populated.
We have an additional ~200uF load capacitance on the output.

We can get the load switch to work correctly if we change R42 to 35.7k and change R45 to 10k (10x lower than the original values).  This fixes the load switch behavior, but results in higher than desired quiescent current draw from the li-ion battery pack.  Again, it is unclear why the original resistor values wouldn't work based on the specs in the datasheet.  

  • 0
    TI__Mastermind 18310 points

    Hi Patrick,

    Welcome to e2e!

    I am looking into this and will update the thread when I have an answer.

    Thanks,

    Patrick

  • 0 in reply to Patrick Shalton
    TI__Mastermind 18310 points

    Hi Patrick,

    In general, the larger the resistance values on EN, the higher the RC constant of the node, and thus the slower the response will be to chances outside of the resistor divider and the less stable VEN will be to external and internal influences. If the resistance gets high enough, the pin will effectively been sees as "floating."

    The increased current draw you see on the EN pin is due to the pin's unstable state as it is constantly changing, and it then makes sense why lower resistor values solve the issue. The data sheet suggests in Figure 64 using 10kOhm as R42 and 2.05kOhm as R45, but this seems like it would result in far too much Iq for your application. Since the stability vs Iq trade-off is application-specific rather than device-specific, I would recommend trying out a few resistor combinations between 35.7k/10k and 357k/100k to see the maximum combination that is stable in your system.

    Additionally, it is best practice to put this resistor divider as close to the EN pin on your layout as possible in order to minimize the size/EMI susceptibility of the EN node.

    Thanks,

    Patrick