When choosing the input voltage range, the input common mode voltage range (VICR) must be taken in to account. If temperature operation is below 25°C the VICR can range from 0V to VCC– 2.0V. This limits the input voltage range to as high as VCC– 2.0V and as low as 0V. Operation outside of this range can yield incorrect comparisons.
The following is a list of input voltage situation and the outcomes:
- When both IN- and IN+ are both within the common-mode range:
- If IN- is higher than IN+ and the offset voltage, the output is low and the output transistor is sinking current
- If IN- is lower than IN+ and the offset voltage, the output is high impedance and the output transistor is not conducting
- When IN- is higher than common-mode and IN+ is within common-mode, the output is low and the output transistor is sinking current
- When IN+ is higher than common-mode and IN- is within common-mode, the output is high impedance and the output transistor is not conducting
- When IN- and IN+ are both higher than common-mode, see Section 2 of Application Design Guidelines for LM339, LM393, TL331 Family Comparators Including the New B-versions.