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    What to do with Unused comparator OpAmps?

    Hello guys!

    I am wondering about how I should connect unused Comparator OpAmps. According to the page number 32 of the next litterature (Bruce Trump):

    https://granasat.ugr.es/wp-content/u...01/slyt701.pdf

    Unused general purpose OpAmps should be connected as ground followers...

    But how should i connect dedicated unused comparator OpAmp like the TLV1704AIPW?

    Thanks in advance!

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    Re: What to do with Unused comparator OpAmps?

    Hi,

    I'd set the inputs with resistive dividers to obtain a high impedance output and in that way not have the device sinking current for nothing/wasting energy pointlessly.

    Nice comparator with no phase reversal, by the way, thanks for bringing it to my attention.

    - - - Updated - - -

    Hi,

    Just saw that the TI pdf is about op amps, not comparators - while it's a delightful conversation topic (where does an op amp end and a comparator truly begin, is a comparator just an uncompensated op amp?, etc.) you are not using an op amp I think.

    Look at the picture on page 32: op amp voltage follower (internally with some push-pull output stage or other). Now look at any old comparator schematic or typical application and spot the big difference: pull-up resistor (on an open collector output). Op amps are analog and linear input and output (hopefully) whereas the comparator is an analog linear input with a "cheapo" NPN inverter digital output.

    All that waffle to explain why I think the ground voltage follower is not a good idea for an unused comparator.


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    Re: What to do with Unused comparator OpAmps?

    Hi,

    I am wondering about how I should connect unused Comparator OpAmps.
    There us no "comparator Opamp".
    It's either a comparator or an Opamp. You should treat them differently.

    An Opamp output is not designed to touch the supply rails, thus bias the noniverting input to supply/2 and connect output to inverting input.
    A comparator output is not designed to stay somewhere inbetween supply rail, thus use a three resistor string between the supply rails an connect the intermediate nodes to the inputs. Don't feedback the output.

    Klaus
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    Re: What to do with Unused comparator OpAmps?

    I doubt that TLV170x quiescent current will change much with input voltage. Biasing the inputs to +/- power supply should work as well.


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    Re: What to do with Unused comparator OpAmps?

    Great! everyhing is clear now. I would tie with a series 10k resistor the Vin(+) to Vcc and the Vin(-) to -Vcc and the output floating. Greetings



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    Re: What to do with Unused comparator OpAmps?

    Hi,

    Great! everyhing is clear now. I would tie with a series 10k resistor the Vin(+) to Vcc and the Vin(-) to -Vcc and the output floating. Greetings
    Iīm not sure if every comparator can handle
    * V_in+ tied to VCC
    * and V_in- tied to -Vcc
    Thus the "three resistor solution" is a solution that will work for every comparator:
    10k - 100R - 10k

    Usually on should avoid "floating" signals, even floating outputs.
    The risk for a floating comparator output causing problems is low...
    Comparators with push-pull-output donīt suffer from floating output.

    For Open_collector / open_drain output comparator is recommend:
    * make "V_in+ < V_in-" then the output is LOW, not floating.
    * for "V_in+ > V_in-" a pullup or pulldown at the ouptut prevents from floating..

    Klaus
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    Re: What to do with Unused comparator OpAmps?

    Iīm not sure if every comparator can handle
    I'm sure some don't. But the question was about TLV170x.



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    Re: What to do with Unused comparator OpAmps?

    Hi KlausST,

    when you mean three resistor solution is this kind of solution:

    Click image for larger version. 

Name:	solution.png 
Views:	5 
Size:	13.6 KB 
ID:	147133


    thanks



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    Re: What to do with Unused comparator OpAmps?

    Hi,

    Yes, if +15V and GND are the supplies for the comparator.
    For open drain/ open emitter I recommend to interchange the inputs to get a low driven output.

    Klaus
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