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LM339 description and what to do with unused gates.


The input voltage range on 1 or both inputs is from -0.3 V to 36 V, independent of the supply voltage.
Input common mode range -0.3 V to VCC-1.5 V.
As long one input is within the common mode range, the output will have the correct state.
If an input is driven below -0.3 V, the current must be limited to < 50 mA.
The comparator should return to normal operation when the excess input current is removed, but I have seen some latch up.
The output can be driven to 36 V, independent of the supply voltage.
The output remains hi-z until the supply voltage reaches 1.5 V to 2 V ( at least on the one I tested ).
An unused comparators should be connected with both inputs on VCC and the output on GND for minimum supply current.

Table 1: Supply current for all valid connections. The 3 other comparators have both inputs and output on GND.
IN+ levelIN- levelOutput stateOutput connected toSupply current, 5VSupply current, 30V
GNDGNDUnknownFloat0.743 mA0.869 mA
GNDGNDUnknownGND0.743 mA0.872 mA
GNDVCCGNDFloat0.741 mA0.866 mA
GNDVCCGNDGND0.741 mA0.868 mA
VCCGNDHi-zFloat0.74 mA0.866 mA
VCCGNDHi-zGND0.74 mA0.866 mA
VCCGNDHi-zVCC0.74 mA0.863 mA
VCCVCCUnknownFloat0.685 mA0.799 mA
VCCVCCUnknownGND0.685 mA0.798 mA

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