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LM139: Output state when one input up to Vcc

Jeramie Bianchi
Expert 3315 points
Part Number: LM139
Other Parts Discussed in Thread: TLV7011

If I’m holding one input at the midpoint by two identical resistors.  Like two 1k resistors so the reference level input is 3.3/2 = 1.65V and the other input will swing up and down 0v to 3.3v while Vcc=3.3V, can we guarantee across the temperature range that the output will also flip correctly accordingly?

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    TI__Mastermind 49876 points

    Hi Jeramie,

    We can not "guarantee" anything that is violating the datasheet specs. But this is a touchy one because the table notes say it can be done...

    Please see section 2.1 of this appnote...particularly section 2.5

    Application Design Guidelines for LM339/LM393/TL331 Family Comparators

    But 1.65V is also above the +1.3V (Vcc- 2V) over temperature specification, so technically both inputs are above the recommended input range - so the "feature" is not valid since both inputs can be out of range.

    If they move the 1.65 down to <1.3V, then "proper' operation is expected. Though, as the appnote states, many specs such as bias current, offset votlage and prop delay will be compromised when one input is outside the limit.

    So the official answer is to use a R-R input device, such as the TLV7011 family. They can also attenuate the input signals so that they are within the valid input range (a 1V signal is just as good as a 3V signal).