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LM556 unused half input termination

Discussion in 'Electronic Basics' started by Rich Grise, May 17, 2007.

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  1. Rich Grise

    Rich Grise Guest

    Crossposted to sci.electronics.design,sci.electronics.basics ;
    followups-to set to sci.electronics.basics.

    I found a 556 in my junque box, and thought it'd be fun to flash an LED or
    something, but I only need one half of it. I know unterminated inputs are
    anathema for digital chips, but what about the spare half of a 556? From
    the schem. on the data sheet,
    http://www.national.com/pf/LM/LM556.html
    http://www.national.com/ds.cgi/LM/LM556.pdf
    it kinda looks like pulling them to either rail might be not too good for
    the chip - what do you guys recommend?

    Thanks!
    Rich
     
  2. D from BC

    D from BC Guest

    I think anything within the datasheet supply rails is allowable to all
    input pins..
    Don't connect the output pin and the open collector to anything.

    In a low current app,look at the datasheet to find out if a L or H to
    the inputs consume more or less current.
    It might be possible to leave all pins loose if the internal op amps
    are not switching to input buzz pick up.. (It's not CMOS.)
    It might consume a tiny bit more current if stuff is switching without
    purpose.

    D from BC
     
  3. John Fields

    John Fields Guest

     
  4. Coleston

    Coleston Guest

    Tie the inputs together and have the output go through a large
    resistor, like 100K to ground. That should do the trick nicely.
     
  5. JeffM

    JeffM Guest

    Only so far as they affect the output.
    Just tie Reset (actually !RESET) low.
     
  6. Rich Grise

    Rich Grise Guest

    Thanks everyone for your answers. Now all I have to do is get up off my
    dead butt and breadboard the thing. :)

    Thanks!
    Rich
     
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