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LM293A: Common mode input voltage problem

Part Number: LM293A
Other Parts Discussed in Thread: LM293, TLV3401, LMC6772

Dear all:

       The schematic diagram is as follows:

Question 1:Our products are all powered by a single power source (i.e., 5V, GND).Should the parameter "common mode input voltage" be considered in the LM293 comparator circuit?

Question 2:Because of the specification

Should the comparator input voltage meet this requirement (Vin+, Vin- less than 3V)?

  • Hello Timsen,

    Yes. You must always observe the common mode limits.

    For the LM293, the input voltage should be less than 3.5V at room temperature, and 3V over temperature. We recommend the 3V limit.

    The first stage, U5A, is at the biggest risk. Both the input and reference voltage exceed the limit and has the possibility of an incorrect output.

    So they need to either change the threshold levels, or, switch to a rail-to-rail input device such as the TLV3401 or LMC6772.