Grounding unused opamps in duals and quads

[Robin]

Why?

[Mike Burgundy]

to avoid any weird effects that *may* occur. It's very likely nothing will happen if you don't, but it is possible that "floating" opamps cause problems like oscillation etc.

[smoguzbenjamin]

It stabilises the opamp.

[The Tone God]

Mr. Murphy and M. Nature have a habit of showing up when you don't want them to. Its a "better safe then sorry" policy that any good designer would adopt.

Andrew

[Robin]

Ok, thanks for the replies.
I guess I was looking for more specifics than "it stablizes the opamp". Take the LM324 (please); the datasheet shows bias circuitry common to all amps, but so what (if no signal is involved)? I 'm guessing capacitive crosstalk wouldn't be an issue.
I agree that it's probably good preventative practice to ground unused opamps on a PCB. I just get frustrated when I'm breadboarding a simple single opamp circuit and all I have handy is a dual. Should be no big deal to leave it hanging in a prototype, yes?

Rob

[Paul Perry (Frostwave)]

On a breadboard, there is no problem leaving an unused op amp section floating.

[Brian Marshall]

what parts do you ground???  I always ground the non inverting input usually through a resistor (i read somewhere a long time ago to do that dont remeber where) and tie the inverting and output together, but dont send it anywhere.

[puretube]

if input not grounded, and output floating, the opamp shows almost infinite open-loop-gain: amplifies the smallest stray signal it picks up to (almost) rail-to-rail "volume". This can cause (HF) oscillation for that particular unused opamp, which can go stray into the rest of the circuit.