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TPS22919: Vout = 0.480V when device output is OFF.

F M
Prodigy 75 points
Part Number: TPS22919

Hello, 

In a LiPo charger circuit, the battery voltage is input to a TPS22919, and the output of this component is then controlled by a power switch circuit.

If the battery is charging, when TPS22919 is disabled, Vout is 0.480V 

If I disconnect the USB cable, which is the input to the charger, Vout goes down to 0.002V.

QOD pin is floating. 

What is causing this voltage?

Thanks

  • 0
    TI__Mastermind 29410 points

    Hi M F,

    When you disconnect the USB cable and VOUT goes to 2mV, is the battery connected?

    Do you see this happening with multiple boards/devices?

    Is there a large output capacitance on VOUT? Or, perhaps the SW_EN net is going high/low repeatedly when it's not intended to?

    Thanks,

    Patrick

  • 0 in reply to Patrick Shalton
    Prodigy 75 points

    Hi Patrick, 

    Thank you for your help.

    When you disconnect the USB cable and VOUT goes to 2mV, is the battery connected?

    Yes, the battery is always connected.

    Do you see this happening with multiple boards/devices?

    I'll be able to test other identical boards early next week

    Is there a large output capacitance on VOUT?

    No cap on Vout and the only load is LED D1 with its resistor R1.

    Or, perhaps the SW_EN net is going high/low repeatedly when it's not intended to?

    I have attached the power switch circuit that controls SW_EN, do you see something wrong?

    Thanks

  • 0 in reply to F M
    TI__Mastermind 29410 points

    Hi F M,

    Understood, thank you for the details. I don't see any issues with the schematic. I'm curious as to why there is any difference between when the charger is connected and when it is not - can you see any reason that can be? The TPS22919 VINs are the same in both cases, right?

    As far as I can tell, there shouldn't be anything that keeps VOUT high unless there is a voltage source on J3 or PWR_LED_A.

    If there isn't, then I recommend testing another board or two (or replacing the unit) to see if this is an application-systematic issue or else if the device may have been damaged.

    Thanks,

    Patrick

  • 0 in reply to Patrick Shalton
    Prodigy 75 points

    Hi Patrick,

    The TPS22919 VINs are the same in both cases.
    There is nothing connected to J3 or PWR_LED_A.

    In a few days, I'll test another identical board and let you know the result.

    Many thanks for checking the schematic.


    Regards,

    Francesco

  • 0 in reply to Patrick Shalton
    Prodigy 75 points

    Hi Patrick, 

    I have tested another board, and the problem is systematic.

    Regardless of the presence of the battery, if the input USB cable is connected, there is a voltage of about 0.48V on Vout.

    At this point, I will start looking for a short between VUSB and VOUT.

    Thanks

  • +1 in reply to F M
    TI__Mastermind 29410 points

    Hi Francesco,

    Yes, it sounds like a short on VUSB and VOUT is the most likely scenario - perhaps there is a resistance that makes a resistor divider with the QOD pin. Please let me know the results.

    Thanks,

    Patrick