LM 339 Comparator Question

Question

Does anyone know if the unused inputs of an LM339 quad comparator need to be stabilized and if so what is the procedure? Since the outputs are open collector I suspect it is ok to leave them floating. I have checked my data sheets but I can't find anything about the unused inputs.

Thanks John

johnbeetem · Accepted Answer

I would suggest pulling up the unused +in and pulling down the unused -in. That way your open-collector outputs are switched off and there's no internal switching generated by noise. JMO/YMMV

dougw · Answer

It should be okay to leave them floating - there should be no excessive current conditions, but it looks like the internal circuit might use a bit more current when the output is low - it is hard to tell because the internal schematic does not show all components in the chip. If there is noise getting to floating inputs, it could cause random switching internally, which could inject some small noise on the power supply.

Doug

DAB · Answer

Hi John,

Even with an open collector output, you might want to ground the inputs just in case you get a static charge build up on the inputs.

I would use jumpers so that you could use the devices at a later date if needed.

DAB

LM 339 Comparator Question

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