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LM339: Input connection consideration

Alessio Bollazzi
Prodigy 10 points
Part Number: LM339

Good Day

The Ti LM339 application note states that inputs should not be connected directly to a low impedance node. In my case does this mean Version A of the circuit is the correct one?  The only difference between the two is the 1k resistor R1.

Regards
Alessio

From www.ti.com/.../SNOAA35

  • 0
    Guru 140200 points

    Hi ALessio,

    yes, looks good Relaxed

    Kai

  • 0 in reply to kai klaas69
    Prodigy 10 points

    Hi Kai

    Thank you very much, could you also tell me if Version B is indeed a bad way to do it?

    Alessio

  • 0
    TI__Guru 54026 points

    Hi Alessio,

    Since both devices are powered off the same supplies, there is little chance of the input being pulled above or below the supplies. The op-amp output would most likely limit the current below any dangerous value.

    If they were powered from different supplies, then I would recommend the series resistor to limit any currents caused by power sequencing during power up/down (more chance of the inputs being pulled beyond the supplies.

    However, if the VREF_5V is derived from another source, then there should be a resistor in series with the input to limit should the VREF line goes above or below the supplies during power up/down.