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 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.
The following 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.