When choosing the input voltage range, the input common mode voltage range (VICR) must be taken in to account. If temperature operation is above or below 25°C the VICR can range from 0 V to VCC– 2.0 V. This limits the input voltage range to as high as VCC– 2.0 V and as low as 0 V. Operation outside of this range can yield incorrect comparisons.
Below is a list of input voltage situation and their 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