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LM139-N: Input voltage

Part Number: LM139-N
Other Parts Discussed in Thread: LM139, LM339

Hi Team,

Can you please help us regarding our customer's inquiry below.

I have a technical question regarding the LM139 which is a very old part. Please see attached. Can you explain what this means because normally BOTH inputs should stay within the common mode range - both top and bottom of the range. I am concerned mainly with the TOP end of the range (VCC-1.5). I am putting 9VDC on the POSITIVE pin of one of the comparators and 5VDC on the MINUS of the same comparator - the VCC supply voltage is 8.5VDC.

Regards,

Danilo

  • The application note Application Design Guidelines for LM339, LM393, TL331 Family Comparators explains the internal circuitry; section 2.5 says:

    A nice feature of the LM339 family (and ONLY applies to the LM339 family devices listed in Table 1-2) is that only one input needs to be within the valid input voltage range for a valid output. The other input can be above the input voltage range or, even above VCC and the output will be in the expected state.
    […]
    While this is a nice feature, it does come at a cost. When operating outside the specified input voltage limits, performance deteriorates and will no longer meet the data sheet specifications. Critical specifications such as offset voltage, bias current and propagation delay will be adversely affected. TI still recommends to stay within the data sheet input voltage range specifications.

  • Hi Danilo,

    Please take a look at the application note referenced in Clemens's comment. Adding on to it, this feature is expected behavior but not warrantied, so operating outside the input voltage limits is still at their own risk. We highly recommend having both inputs within the common mode range if possible.

    Thanks for the question!

    Chi

  • Hi Clemens and Chi,

    Thank you very much for this information.

    Regards,

    Danilo