LM556 unused half input termination
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Posted by Rich Grise on May 17, 2007, 12:42 pm
Please log in for more thread options 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 | ||||||||||||||||
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Posted by D from BC on May 17, 2007, 1:27 pm
Please log in for more thread options 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 | ||||||||||||||||
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Posted by John Fields on May 17, 2007, 1:47 pm
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wrote: >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? --- It's bipolar so no big deal, but if I wanted to nail everything down I'd run THRESHOLD and RESET low, TRIGGER high, and let the rest of it float. -- JF | ||||||||||||||||
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Posted by Coleston on May 17, 2007, 2:08 pm
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> Crossposted to sci.electronics.design,sci.electronics.basics ;
sheet,http://www.national.com/pf/LM/LM556.htmlhttp://www.national.com/ds.cgi/LM/LM556.pdf
> 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 > it kinda looks like pulling them to either rail might be not too good for
> the chip - what do you guys recommend? > > Thanks! > Rich Tie the inputs together and have the output go through a large resistor, like 100K to ground. That should do the trick nicely. | ||||||||||||||||
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Posted by JeffM on May 17, 2007, 2:24 pm
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Rich Grise wrote: >I found a 556 in my junque box[...]
Only so far as they affect the output.
>I know unterminated inputs are anathema for digital chips, > >but what about the spare half of a 556?
Just tie Reset (actually !RESET) low.
>From the schem. on the data sheet[...]it kinda looks >like pulling them to either rail might be not too good for the chip > | ||||||||||||||||
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>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