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LM556 unused half input termination

R

Rich Grise

Jan 1, 1970
0
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
 
D

D from BC

Jan 1, 1970
0
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

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
 
J

John Fields

Jan 1, 1970
0
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?
 
C

Coleston

Jan 1, 1970
0
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.htmlhttp://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

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

JeffM

Jan 1, 1970
0
Rich said:
I found a 556 in my junque box[...]
I know unterminated inputs are anathema for digital chips,
Only so far as they affect the output.
but what about the spare half of a 556?
From the schem. on the data sheet[...]it kinda looks
like pulling them to either rail might be not too good for the chip
Just tie Reset (actually !RESET) low.
 
R

Rich Grise

Jan 1, 1970
0
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 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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