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Unconnected Opamp Pins

Thread starter #1
I am using only 2 out of 4 opamps of a quad opamp. in an application note it is said that the unused pins of opamp shouldn't be left floating. They have given following layout for connection of unused opamp
Source :Texas Instrument
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One thing I don't understand in this is the Half Supply. P.S. I am giving +15 and -15 V supply.
Someone please explain me what half supply here means.
Thanks
 

dknguyen

Well-Known Member
Most Helpful Member
#2
Half supply is halfway between the positive and negative power rails going to the op amp so that neither the lower or upper output stages are pushed in saturation and are at their most balanced. The most "neutral" state of the op-amp, so to speak. In your case that's 0V.
 
Thread starter #4
Half supply is halfway between the positive and negative power rails going to the op amp so that neither the lower or upper output stages are pushed in saturation and are at their most balanced. The most "neutral" state of the op-amp, so to speak. In your case that's 0V.
So if I am giving +15 V and 0 V, then will the half supply be 7.5V? If yes, from where will I generate it?
 

rjenkinsgb

Active Member
#6
If you are using a dual supply, connect the positive input to 0V.

With a single supply, if the opamp is a type that includes ground (= negative supply) as part of its permitted input voltage range you can simply connect the positive inputs to ground / negative supply.

Either way, link output and negative input.

The bias circuits are only needed if you have a single supply and an opamp where the inputs cannot tolerate connection to negative.
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
#8
One of the criteria is to prevent oscillations and the other one is to minimize power consumption.
So a unity gain dual symmetrical supplies OP-amp would not be turning on it's output stage under those conditions.
You can also arrange stuff so that if you needed to make a design change that required a spare OP-amp it would have easy access.
 

unclejed613

Well-Known Member
Most Helpful Member
#9
You can also arrange stuff so that if you needed to make a design change that required a spare OP-amp it would have easy access.
the usual method is to have traces available on the "unused" pins, and a solder blob or jumper between the inverting input and output and either a solder blob or a jumper from the noninverting input to ground or Vcc/2.
 

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