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LM76202-Q1: SHDN pin activated by human touch

Robert Gilmore
Prodigy 30 points
Part Number: LM76202-Q1

I'm using the LM76202Q as a protection chip for my circuit. I have the \SHDN pin routed to an external connection "KEY_IGNITION". Sometimes, when this is touched by hand, the output of U1 is activated, other times it is not. I have found it turns on consitently if I touch 12V with one hand and then the "KEY_IGNITION" connection with the other.

 

I think I should reduce the value of R5 to cause a stronger pull down on \SHDN.

 

Can someone please advise and review the circuit in general?

https://www.ti.com/product/LM76202-Q1

LM76202_QueryTouch.pdf

  • 0
    TI__Guru** 105361 points

    Hi Robert,

    Welcome to E2E!

    What is the voltage you are seeing at \SHDN under those cases? you can reduce R5 if it is DC voltage or consider adding small cap in parallel with R5 if it is voltage spike caused by discharge of ESD from your body.

    Best Regards

    Rakesh

  • 0 in reply to Rakesh
    Prodigy 30 points

    I measured when touching the 12V with 1 hand and "KEY_IGNITION" with the other. 

    Initially got 0.87V.

    Then with moisture on each hand got up to 4V on "KEY_IGNITION".


    What value for R5 do you recommend and why?

  • 0 in reply to Robert Gilmore
    TI__Guru** 105361 points

    Can you share the waveform in oscilloscope. Is it a DC or AC voltage. ?

    Can you share the control logic and expected voltage at SHDN/ in normal condition. You want to keep eFuse in OFF by default with R5 pull-down ? What is the "KEY_IGNITION"  in HIGH level (is it 12V or 5V)  ?

    Best Regards,

    Rakesh