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LM119: LM119

Jorge Vega
Prodigy 80 points
Part Number: LM119
Other Parts Discussed in Thread: LM111

Hello, I am using a quad channel LM119 with one not being used.  Can you advise the proper way to wire the comparator that is not being used. LM119 is an open collector comparator.

1. Can the spare comparator be wired as shown in the image 1 (what problems may the comparator have if wired like this?)

2. Can the comparator be wired as in image 2 (what problems may the comparator have if wired like this?)?

5226.Comparator.pdf

Thank you,

Jorge Vega

  • 0
    TI__Guru 53816 points

    Hello Jorge,

    The inputs should be held within the specified legal voltage range, which is 0.5V above V- to 2V below V+. You did not mention the intended supply voltages (split supplies?).

    Both images would violate the negative input range.. You also should not separate the inputs by more than 10V.

    I have not verified it, but pinching off the input stage by pulling it outside the valid range could possibly disturb the shared internal biasing with the used channel.

    So I would recommend tying the inputs to some voltage points that are within the legal range, but separated by more than 10mV to prevent chatter. Could you possibly borrow the reference voltage for the used channel?

    I would also use 1k resistors instead of zero ohms in case there are any transients.

    If you just need a single channel with the "floating" output, the LM111 has similar functionality, but is slightly slower.

  • 0
    TI__Genius 13550 points

    Hi Jorge,

    I would like to know why you are using a dual comparator if only one channel is used? The LM111 has the same operating temperature range as the LM119 and a similar supply range.

    As far as the two of the provided configurations, I would like to know your supplies so I can determine the input common mode voltage range.

    Kind Regards,

    Joe

    All information in this correspondence and in any related correspondence is provided “as is” and “with all faults”, and is subject to TI’s Important Notice (www.ti.com/.../important-notice.shtml)

  • 0
    Prodigy 80 points

    Hi Paul, thank you for your reply.  Your name sounded familiar and it was from a Bob Pease (RIP) video I had seen.  Luck you to have met him!.  Thanks again for taking my question.

    Back to the comparator.  I am using a single ended supply 0V to 10V.  From your reply and from the D/S I see that the the inputs need to be at 1V away from the ground and 2V away from the voltage rail.  I am reading the line item circled in red in the image below.  the record above the circled item, shows that for a split supply, the inputs need to be 2V away from either positive or negative rail.  which is it 2V or 1V or perhaps I misread the D/S.

    The pdf below shows how I am wiring the comparator's unused channel.  I am using the other three comparators without issues.

    Many thanks, Jorge Vega NGC

    The PDF:

    Comparator1.pdf

    (https://www.ti.com/lit/ds/symlink/lm119.pdf?ts=1632244816025&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLM119)

  • 0 in reply to Joe Vanacore
    Prodigy 80 points

    Hi Joe,

    We are using 3 channels out of 4.  The question is about the unused channel.   The supply voltages are 0V to 10V, so single ended supply.  Many thanks!

    Jorge

  • 0 in reply to Jorge Vega
    TI__Guru 53816 points

    Hi Jorge,

    Yes, Bob was quite a character. I was lucky to have worked for and with him.

    Yes. The line you highlighted is for a single 5V supply. Input range is 1 to 3V on a 5V supply. Since the devices of this era were designed for split supplies and in mostly mid-supply zero crossing applications, sensing to the rails was not required.

    So you will need to keep the input signal within +1V to +8V on a single 10V supply to prevent reversals or increased prop delay. I'm not really sure why the original authors had the split supplies be 2V from each rail, and single at 1V from V-. Stay 2V away if you are concerned...but I don't think there should be an issue at 1V.

    The unused comparator circuit looks fine.

  • 0 in reply to Paul Grohe
    Prodigy 80 points

    Thanks for your help!