If we use a dual in package comparator Example LM2903 and do use only one comparator, what should be done with the other one. It is sure that paralleling the two comparator will cause instability and we cannot leave that comparator unconnected too. Are there any inputs how it can be connected?
Electronic – Dual Comparators connection that affect the design
comparatordual
Related Solutions
I would not bother trying a "quick fix". I would instead try the following circuit
simulate this circuit – Schematic created using CircuitLab
Basically, it requires the addition of 1 op amp and two diodes. I've shown a TL081 as the op amp, and this will work in simulation down to 1 mV or less, but it eventually runs into input offset voltage problems. If you can find an op amp with much less input offset, you can do even better. For a real circuit, get an op amp which includes an offset adjust pin, and use this to produce an op amp output of zero with zero input.
You'll also note that the comparator output is inverted with respect to the input, but that is easily remedied in logic.
EDITED TO ADD - And in the name of all that's holy, get rid of the 1N2804. It's a 50-watt zener, and is operating far below its recommended current level. A 1N4735, as shown, has a 6.2 volt rating and appropriate current levels.
This application note answers exactly your question and covers a few less obvious issues associated with incompatibilities that may arise due to the different optimization and expected usage of op-amps and comparators. Give it a read:
https://www.analog.com/en/analog-dialogue/articles/amplifiers-as-comparators.html
Best Answer
The LM2903 is a bipolar comparator and you can safely leave all the unused connections open.
If it's a CMOS-input comparator then it would be best to tie the inputs to some known voltage within the power supply range.
If you are doing something especially critical (sub-mV) you may wish to bias the inputs so the output is in a known state (which means the inputs are at different voltages within the common-mode range)- because the bias networks tend to share a few parts there might be a slight effect of one comparator on the others. Unused output(s) can always be left open, whether open drain/collector or push-pull. You can ground unused open drain/collector outputs if you want, but it doesn't matter.