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TPS22919: TPS22919 Output still biased when ON pin is low and output pulled low with 1k through QOD discharge output.

Danny Cornelissen
Prodigy 20 points
Part Number: TPS22919

Tool/software:

TPS22919 Circuit.pdf

Dear technical expert,

We see some strange behaviour when we switch the ON pin (pin 3) from 3V and then back to 0V,  the output with the QOD resistor of 1K (which is pulled by the QOD pin to ground) we still measure a output bias voltage of approx 1V.  

When we connect a low enough value resistor to the QOD pin (R104 approx. 100 Ohm) at that point the output will be switched of and will not be be biased anymore and the output current drops to <1uA.

Why is there an output current of approx. 1mA still flowing why the ON pin is < 0.35V?

And what is a safe value of the QOD resistor to be absolute sure the output is switched off?

Thanks in advance.

  

  • 0
    TI__Mastermind 38465 points

    Hi Danny,

    It looks like when you are keeping 1kohm resistor, even with current as small as 1mA, you will see 1V at output. When you reduce the resistor, the vout also reduces. Now the important question is what is the cause for this current. 

    Do you have anything else connected at the output other than what is shown in the attached schematic.

    I don't expect device to leak 1mA current between IN and OUT. I am just mentioning few things that might help in debugging this issue.

    • Just check the voltage at ON pin. Maybe use stronger pull down at ON.
    • Disconnect all the loads at the device output and verify this again.

    Please let me know if this helps or if this doesn't help.

    Best Regards,
    Arush 

  • 0 in reply to Arush Gupta
    Prodigy 20 points

    Dear Arush,

    Thanks for your suggestions.

    We did some voltage measurements and wrote this down on the schematic below.

    Indeed we provide some source current into the output through resistor R109.

    But not enough to lift up the R104 QOD resistor to a voltage level of 1.12V

    It seems by sourcing a small amount of current into the output will cause a bias current from the TPS22919 from the input to the output, is that possible?

    Thanks.

    Best Regards,

    Danny

  • 0 in reply to Arush Gupta
    Prodigy 20 points

    Dear Arush,

    Thanks for you help and we finally solved the issue.

    When the TPS22919 switches off the voltage at the output will drop.

    During the drop of the voltage there is a point where the SELECT pin of U16 TMUX will pass a voltage of 1V. (see the attached schematic)

    This SEL voltage of 1.0V will result to internally connect the S1 to S2 pin and current can be flown from VREF (2V) to +3V3_CHG_EN.

    This current will lift the TPS22919 output to 1.12V and stays at this level.

    Best Regards,

    Danny Cornelissen

  • 0 in reply to Danny Cornelissen
    TI__Mastermind 38465 points

    Hi Danny,

    Thank you for the update. Always happy to help :) 

    I am closing this thread. For follow up questions, you can reply back here or create new thread and include this thread's link. 

    Best Regards,
    Arush