# Input ranges exceeding rails in opamps & comparators

With opamps & comparators datasheets I've seen, it was typical to show in absolute maximum ratings values such as:

$$V_{SUPPLY} (V_{DD} \; to \; V_{SS}): \quad 12V$$ $$V_{DIF\_IN} (V_{-IN} \; to \; V_{+IN} ) : \quad 10V$$

It was almost common sense that the input signals individually go like this as well:

$$V_{SS} - 0.1V \le V_{-IN} \le V_{DD} + 0.3V$$ $$V_{SS} - 0.1V \le V_{+IN} \le V_{DD} + 0.3V$$

(where the -0.1V & +0.3V are generous leeways given by the implementors, as much as exceeding rails go)

Yet it was hardly specifically ruled out that inputs should stay within the supply rails. Since it's difficult to imagine how to implement an amplifier package where the inputs are not bounded by any rails, I simply assumed that the inputs indeed are bounded (as the last 2 math expressions). The documenters of the datasheet was simply writing it in terms of brevity.

Yet now, I'm dealing with a circuit where it's convenient that $$\V_{-IN} > V_{DD}\$$ & $$\V_{+IN} > V_{DD}\$$ & $$\V_{DIF\_IN} \ge V_{+IN} - V_{-IN} \ge 0\$$. So could anyone clarify if there are some opamps/comparators that indeed only care about differential inputs & not if they exceed the rails?

• If you want to build a difference amplifier circuit, then consider that these can have input common ranges exceeding the supply rails, even for regular op-amps. It's a result of the two input resistors dropping the excess voltage. Commented Apr 25 at 4:18