OPA2991: OPA-x991 output impedance at DC

James Wilson2

Part Number: OPA2991
Other Parts Discussed in Thread: TINA-TI

Is there a figure available for the open-loop output impedance of the OPA-x991 at DC? The datasheet has a figure at 1 MHz and a chart that goes from 100 - 40 MHz. The chart for another part, OPA-192, goes down to DC and the result is different than the 1 MHz figure, so I would not assume to extend the line on the OPA-x991 chart. My design goal is to buffer a DC voltage divider reference at < 0.1 ohm source resistance.

over 3 years ago

0 Ron Michallick over 3 years ago

TI__Guru*** 139826 points

James,

In your case, a closed loop Zo is the parameter in question. Basically dVos / dIOUT which is best in unity gain. What is the range for output current needed?

0 James Wilson2 over 3 years ago in reply to Ron Michallick

Prodigy 30 points

I'm not sure I follow you. I'm using the same reasoning explained in the INA-849 datasheet for using a buffered voltage divider as the reference input: that the output impedance is the open-loop Zo reduced by Aol. They use an OPA-192 which has data for both going down to DC, but 100 Hz is the lowest I see in the OPA-x991 datasheet.

As it would be connected to the input network of another op amp, output current for the voltage reference would be ideally near zero, with small signal variation that must be at low impedance for the INA-849 to have good CMRR.