I have two versions of the input signal:

- 5V inactive level, 3.2V active;
- 5V inactive level, 0V active level.

Thinking on making universal circuit to support both signals, I decided to use comparator, having threshold voltage at about 4V. Here's the circuit:

[![enter image description here][1]][1]

I built a prototype, and it shows unexpected (for me) behavior:

[![enter image description here][2]][2]

Red is voltage on positive input pin, yellow is on negative. **Capacitor C58 was removed.**

Searching through internet I found [this question][3]. It is about operational amplifier, and not about comparator. But I took a closer look into the [datasheet][4], and found the following:

> Differential Input Clamp Voltage --- VCC = 5.5V, VIN- = 0V, IIN+ = 100µA --- 2.1 V

Is it the information I should be looking at? Does it mean that voltage between + and - inputs must be not larger than 2.1 V, otherwise there will be current path between the inputs? Is it naive to assume that if I have **comparator** powered from 5V, that it must be able to properly handle differential voltages on the whole power scale? And why datasheet does not state that there's such a limitation in its headline?

  [1]: https://i.sstatic.net/4jIv8.png
  [2]: https://i.sstatic.net/0SuCQ.png
  [3]: https://electronics.stackexchange.com/questions/437745/reference-voltage-changes-when-connected-to-inverting-input-of-op-amp-comparator
  [4]: http://www.redrok.com/Comparator_MAX961-MAX999_5nS_5mV_Latch_R-R_3V-5V.pdf