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Original question:

LMV331 Comparator - output voltage with no power to ic

LMV331: Can damage to an ESD diode cause the open collector output of the LMV331 to be "stuck at 1"?

James Dupre51
Prodigy 160 points
Part Number: LMV331

Is it correct that the open collector output of the LMV331 has ESD protection diodes? If so, is it possible that the open collector output could become damaged and be "stuck at 1" aka "stuck high", possibly by an EOS event that causes the protection diode from the output to the VDD rail to become shorted.

Regards,
James 

  • +1
    TI__Mastermind 49856 points

    Hello James,

    If it is stuck at high, then either the output transistor is not conducting or the output is shorted to V+, assuming V+ is the same as pull-up voltage.

    If the ESD diode is truly shorted, you should be able to measure a low impedance (several ohms) between V+ and OUTPUT with the power off.

    The LMV331 does have ESD protection diodes from every pin to both V+ and V-, so the output cannot be pulled-up higher than V+.

    Can you provide a schematic and/or scope photos so we can make sure the operating conditions are correct.

  • 0 in reply to Paul Grohe
    Prodigy 160 points

    Thank you Paul for your prompt and detailed response. My question was purely hypothetical, because the LMV331 is used in a circuit for safety reasons. So if the output were ever to get stuck high - which seems like is a possibility, albeit not a likely one - then we would not be able to rely on the output going low to activate our safety circuitry.

  • +1 in reply to James Dupre51
    TI__Mastermind 49856 points

    Hi James,

    "stuck" high would imply that the output transistor and/or comparator was blown, and can no longer sink current. If the comparator was non-functional, the default output would be high as there is nothing to "pull-down" on the pull-up resistor.

  • 0 in reply to James Dupre51
    Guru 140200 points

    Hi James,

    one remedy is to increase the redundance by using more than one LMV331 circuit and to link the outputs of identical LMV331 circuits by the wired-or technique including isolation diodes:

    Or even this way, like in "EX" circuits:

    But in any case you should add protection and filter circuitry to make the circuit immune against ESD, Surge and Burst. Don't allow EMI to enter your board. Shunt EMI to a suited radio frequency plane before it has the chance to enter your board. A completely surrounding metal enclosure (Faraday cage !) is a perfect radio frequency plane by the way Relaxed

    Kai

  • 0 in reply to kai klaas69
    Prodigy 160 points

    Thank you Kai. We had used this approach in the past for a similar purpose (the first method, with the outputs wire OR'd a single diode on each output). I'll use this approach again thanks to your suggestion.