Hi all,

The OPA337 datasheet states that :

The OPA337 series is unity-gain stable. The OPA338 series is optimized for gains greater than or equal to 5.

Can the OPA337 be used for gains greater than 5, or just as a unity gain IC ?
I am planning to implement an amplifier with a variable gain from 1 to 10. Since it can be set to unity gain (A = 1), I was opting for a unity gain stable op-amp. But are they good for gains greater than 1 ?

 

Yes, you can use this op amp. It is important not to exceed the load capacity.

 

Just because it's guaranteed stable down to a gain of one doesn't mean they revoked the stability at higher gains.

 

Unity gain has more chance of oscillating over a higher gain as the feedback signal is the largest.

 

The more feedback, the higher the chance of oscillating.
So if the op amp is (non-inverting) unity-gain stable, with a feedback gain of 1, then it will be stable at higher gains, where the feedback gain is less than 1.

 

Unity gain is most problematic as the feedback is greatest.

Higher gains are more stable.

(don't snooze before hitting send or someone will beat you to your point.)

 

(don't snooze before hitting send or someone will beat you to your point.)

Sorry. I was in the kitchen making coffee. What were you saying?

 

Thanks for the replies. Is greater feedback/more feedback referring to higher gain? I cannot really understand when the OPA337 (a unity gain stable op-amp) gets unstable. How can I know that the op-amp will work correctly with gain varying from 1 to 10?

 

I cannot really understand when the OPA337 (a unity gain stable op-amp) gets unstable.

It doesn't get unstable for any gain equal to or greater than one.

How can I know that the op-amp will work correctly with gain varying from 1 to 10?

1) We just told you it would.
2) The datasheet told you it is stable down to a gain of one volt per volt.
That means it is stable for all gains equal to or greater than one.

 

Read a good op amp book because this subject is much deeper than this forum can go into.