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 V. This limits the input voltage range to as high as VCC– 2 V
and as low as 0 V. Operation outside of this range can yield incorrect comparisons.
The following list
describes the outcomes of some input voltage situations.
- 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