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Used one OpAmp as Amplifier and another as Comparator in a ADA4891-2ARMZ chip. Can the usage of a OpAmp as a Comparator for this device cause any trouble, wear-out etc.

oleskott
on Mar 21, 2017

AN-849 advise against the usage of a OpAmp as a Comparator and someone mentioned that ”the OpAmp transistors can wear out over time and there is a risk that it may happen too fast” Is this fear reality or not?

In our practical example it’s very convenient to use a part with two OpAmp’s as we need a OpAmp for amplifying the current measurement and a Comparator for detecting passing a threshold level.

Thanks in Advance, Ole.

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  • FormerMember
    0 FormerMember on Mar 21, 2017 9:02 PM over 4 years ago

    Comparators, Op Amps, and InAmps are shown as triangles with two inputs and one output;  they are not the same.

    A comparator is decompensated, has a digital output stage, gets faster w/ overdrive, and usually will allow a wide

    differential voltage on the inputs.  Also, if it's RR output, supply current can be quite high;  see MS-2212

    http://www.analog.com/media/en/technical-documentation/technical-articles/MS-2212.pdf 

    Finally, depending on how the internal current sources are biased, there may be some common circuitry

    for duals and quads, so when one section is in an abnormal condition, it may affect the other section(s).

    In the semiconductor industry, we normally don't test for this or tell you about it.  The only mention I have

    seen is page 9 of the LT1013 data sheet.

    There is a single version of the ADA4891-1.

    Customers can connect our parts any way they want to, but considering the size and reputation of your

    company, I would not put this design in a production system.

    Harry

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  • FormerMember
    0 FormerMember on Mar 21, 2017 9:02 PM over 4 years ago

    Comparators, Op Amps, and InAmps are shown as triangles with two inputs and one output;  they are not the same.

    A comparator is decompensated, has a digital output stage, gets faster w/ overdrive, and usually will allow a wide

    differential voltage on the inputs.  Also, if it's RR output, supply current can be quite high;  see MS-2212

    http://www.analog.com/media/en/technical-documentation/technical-articles/MS-2212.pdf 

    Finally, depending on how the internal current sources are biased, there may be some common circuitry

    for duals and quads, so when one section is in an abnormal condition, it may affect the other section(s).

    In the semiconductor industry, we normally don't test for this or tell you about it.  The only mention I have

    seen is page 9 of the LT1013 data sheet.

    There is a single version of the ADA4891-1.

    Customers can connect our parts any way they want to, but considering the size and reputation of your

    company, I would not put this design in a production system.

    Harry

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