OPA726: OPA726 - does enable pin put the output in a high-impedance state

Hi Kevin,

if the datasheet doesn't explicitely say that the output becomes high ohmic, then I would not rely on it. Keep in mind, that the shutdown feature of OPA726 is mainly to reduce the supply current and not to support multiplexing applications.

Kai

Hi Kevin,

The datasheet is unclear on the device behavior in shutdown although typically shutdown does mean high impedance output pin. We have some samples of this device in our lab, let me put one on the bench and test it to see how it behaves in shutdown. If you could give me a day or two to get back to you on this, that would be appreciated.

Best,
Paul

Thanks Kai, I would assume the same thing, but am also looking for a solution that will put the output in high-impedance for my design.

Hi Paul, that would be a great help if you could see how it acts in shutdown mode. Let me know when you have some answers. In my application, I'm focused on a +-5V application, but any insight would be a help. I hope to hear from you in a few days.
Thanks!

Hi Paul,

Do you have any information on the output reaction of the OPA726 when in disabled mode with an active AC signal being driven from another chip? Is the output still very high impedance or does it become reactive?

Thanks,
Kevin

Hi Kevin,

I did not test this impedance across frequency but the output impedance will almost certainly become reactive. We model this as a parallel capacitor and resistor and for newer devices is specified. For example, the TLV9062:

ZSHDN: Output impedance during shutdown: 10GΩ || 2pF

These shutdown impedance pretty quickly roll off into the 100s of kilo-ohms region. What frequency are you thinking might be driven into the output pin when shutdown?

-Paul

Hi Paul,
We'd be expecting 1KHz to 100KHz range being seen at the output - likely across the +-5V range (what the rails would be).
Thanks again,
Kevin

Hi Kevin,

don't forget the components in the feedback loop... Can you show a schematic?

Kai

Hi Kai,
I am aware of the feedback and output impedance of the design. I'm just concerned about the output characteristics of the op-amp in shutdown mode.

Thanks Paul,
I think I'm confident to move forward. I appreciate all you help and insight.