question on LM393

Discussion in 'General Electronics Chat' started by ayane, Oct 11, 2009.

  1. ayane

    Thread Starter Active Member

    May 3, 2009
    i got a little confused with the lm393 datasheet.

    on page 8 they state the that all input pins of any unused comparators should be connected to the negative supply .

    eg: what if i am using the a single supply hence all the input pins of any unsed comparators should be connected to the ground?..


    heres the link:
  2. hgmjr

    Retired Moderator

    Jan 28, 2005
    That is a legimate solution to the unused inputs pins for the single supply application of the LM393.

  3. rogs

    Active Member

    Aug 28, 2009
    Couple of other points from the data sheet that may not concern you, but can cause havoc if encountered by mistake!

    Top of page 5 : notes 6 and 8.

    If there's any chance of your inputs going negative to the negative supply rail (ground in your case), by more than 300mV, then fit a current limiting series resistor in series with the input (typically 10k- but dependent on the magnitude of the negative going signal. ).
    Without it, you will probably destroy the ic, with a negative input signal.

    Second note - don't forget that your reference input must be at least 1.5V below your positive supply rail. If it's closer, the comparator may behave very strangely (although probably not destroy itself!)
  4. ayane

    Thread Starter Active Member

    May 3, 2009
    thanks noted the important points.