OPA549: Output swings to V+ with a floating input.

Sriman Kamarajugadda

Part Number: OPA549

I am using OPA549 as a voltage follower. I observed the op amp output swings to V+ when the non inverting input terminal is floating. Is this expected?

over 4 years ago

0 kai klaas69 over 4 years ago

Guru 140200 points

Hi Sriman,

yes, that is expected. For the input bias current you must create a path to signal ground, for instance, by the help of a resistor.

Can you show a schematic?

Kai

0 Sriman Kamarajugadda over 4 years ago in reply to kai klaas69

Prodigy 50 points

Hello Kai,

Thanks a lot. I figured I needed a pull down to avoid this; but did not know this is due to the bias current. Would you be able to share a link for a more detailed explanation for the need of a return path for input bias currents?

Here is the circuit.

Amplifiers

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OPA549: Output swings to V+ with a floating input.