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TPS1H200A-Q1: Why we need to add one resistor when detecting open fault?

Sherry Liang
Genius 10255 points
Part Number: TPS1H200A-Q1

Dear team,

I have two questions for our open load detection. The first question is why the output voltage is close to the supply voltage if an open load occurs? In my understanding, the output should be floating because the internal mosfet is open. The second question is that why the pullup resistor can offset the leakage current. What is the bad impact if leakage current existing?

Thanks & Best Regards,

Sherry

  • 0
    TI__Genius 16390 points

    Hi Sherry,

    Let me try to answer your questions:

    1. The output is high due to the external pull up resistor. When the output is floating, the pull up resistor will pull the output voltage high for the open-load detection.

    2. Leakage current is the current exists in the logic path to the ground. Although the output is open, the outside humidity can have a similar effect of a resistance, and form a closed loop circuit. If there's leakage current in the path, then it has potential of triggering the internal logic when it not supposed to. Having an external pull up resistor will short out the path through the internal logic.

    Please let me know if you have additional questions.

    Regards,

    Yichi

  • 0 in reply to Yichi Zhang.
    TI__Genius 10255 points

    Hi Yichi,

    Thanks for your help! For the item 1, I can understand. But I don't understand the item 2. Could you please help mark where the leakage current path is?

    You said  it may trigger internal logic, you mean it may turn on the mosfet?

    Thanks & Best Regards,

    Sherry

  • +1 in reply to Sherry Liang
    TI__Genius 16390 points

    Hi Sherry,

    This is the leakage path. R1 is the input impedance of the logic circuit inside IC, and R2 is due to humidity etc. from the output to ground.

    The pull up resistor will short R1 in this case and help not to trigger any internal logic unintentionally.

    Regards,

    Yichi