How to Handle Unused Op Amp Sections?

[N. Thornton]

may use power, depends.

I think it depends on your opamp. I have often used CMOS invertors as
opamps - or should I say in lieu of opamps. With those you need unused
outputs to be 0 or 1, not half way, which eats power.

You could also connect the +input to the output, its just as stable.
LM324s seem happy enough unconnected, though I wouldnt rely on that.


Regards, NT

 

[PaulCsouls]

I have a design where I am using 3 of the four sections of a TL074 Quad Op
Amp. What should I do with the unused pins, especially the inputs, on the
fourth Op Amp to prevent it from causing any problems?
Thanks,

If you don't mind the additional parts, put 1k resistors from each
input to ground and a 1k negative feedback resistor. It makes it easy
to use the amp for prototyping. A cap across the feedback resistor is
nice too. The next project often starts where the last one left off.

Paul

 

[Tom Del Rosso]

In John Woodgate typed:

I read in sci.electronics.design that Tim Dicus <[email protected]>


You are using a different definition of 'ground'.

Ground is ground
the world around
except in England
where it's Earth.

But I've seen it suggested in data sheets to ground only (+) and use
negative feedback to make sure the inputs are equal, I guess to
compensate for Vos.

 

[Tim Dicus]

In John Woodgate typed:

Ground is ground
the world around
except in England
where it's Earth.

But I've seen it suggested in data sheets to ground only (+) and use
negative feedback to make sure the inputs are equal, I guess to
compensate for Vos.

Connecting the non-inverting input to ground is recommended only if using a split supply (V+ and V-).

If one plans to use a single supply (V+ and ground), I would recommend V+/2 on the non-inverting input. Otherwise, the inputs may be
out of common mode range.

I had made a statement earlier in this thread about ground, when I was actually refering to the negative power supply (V-). I was
incorrect to imply they are aleays the same voltage level. In many cases, they are not.

But in this case, they are.

Tim

 

[NCSRadio]

If you don't mind the additional parts, put 1k resistors from each
input to ground and a 1k negative feedback resistor. It makes it easy
to use the amp for prototyping. A cap across the feedback resistor is
nice too. The next project often starts where the last one left off.

Paul

Thanks Paul - I just may do that!

 

[Tom Del Rosso]

In Tim Dicus typed:

Connecting the non-inverting input to ground is recommended only if
using a split supply (V+ and V-).

Right. I assumed a split supply, but I shouldn't have.

 

[Stefan Heinzmann]

I have a design where I am using 3 of the four sections of a TL074 Quad Op
Amp. What should I do with the unused pins, especially the inputs, on the
fourth Op Amp to prevent it from causing any problems?

This might be of interest:

http://pdfserv.maxim-ic.com/en/an/AN1957.pdf

 

[Genome]

I have a design where I am using 3 of the four sections of a TL074 Quad Op
Amp. What should I do with the unused pins, especially the inputs, on the
fourth Op Amp to prevent it from causing any problems?
Thanks,

Use a petrol 'skillsaw' with a diamond tipped blade to remove the offending
quarter. Make sure you get someone else to hold the device whilst doing so.
If you can't find someone silly enough superglue it, legs facing upwards, to
something stable but expensive.

Save the quarter for when you have a circuit which requires a single op-amp.

No Worries

DNA

 

[Carey Fisher]

This might be of interest:

http://pdfserv.maxim-ic.com/en/an/AN1957.pdf

Thanks Stefan. This is just what I need!!

 

[Cornholio]

Tie the inverting input to the output and ground the non-inverting
pin. (Voltage follower config with 0V input)