When choosing the input voltage range, the input common mode voltage range (V_ICR) must be taken in to account. If temperature operation is above or below 25°C the V_ICR can range from 0V to V_CC – 1.5V. This limits the input voltage range to as high as V_CC – 1.5V and as low as 0V. Operation outside of this range can yield incorrect comparisons.

Below is a list of input voltage situation and their outcomes:

1. When both IN- and IN+ are both within the common mode range:
   1. If IN- is higher than IN+ and the offset voltage, the output is low and the output transistor is sinking current
   2. If IN- is lower than IN+ and the offset voltage, the output is high impedance and the output transistor is not conducting
2. When IN- is higher than common mode and IN+ is within common mode, the output is low and the output transistor is sinking current
3. 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
4. When IN- and IN+ are both higher than common mode, please see the Both Inputs Above Input Range Behavior section of the LM339 Family Application Note (SNOAA35).