OPA197: Closed-loop output impedance over frequency

KKF

Part Number: OPA197
Other Parts Discussed in Thread: TINA-TI

Hi,

Do you have a curve showing OPA197 output impedance over frequency at closed loop gain of 1, 10 and 100?
Or a formula to calculate the closed-loop output impedance from the open-loop output impedance curve in the DS?

Thanks a lot in advance and best regards,

over 4 years ago

0 kai klaas69 over 4 years ago

Guru 140200 points

Hi KF,

the easiest way would be to do it in TINA-TI :-)

Kai

0 KKF over 4 years ago

TI__Expert 4385 points

Hi Kai,
Is there a link or guideline I can share with customer how to do it in TINA?

Thanks,
KF

0 Michael Steffes over 4 years ago in reply to KKF

Guru 48395 points

Just drive a current source into the output and measure the voltage, here is gain of 1 - dBohms plot,

can't paste in snip now, that has changed since yesterday, how do I put in a picture now.

+1 Raymond Zhang1 over 4 years ago in reply to KKF

TI__Guru 63151 points

Hello KF,

Please see that attached Op amps - Trust but Verify pdf. The transformation from open-loop output impedance (Zo) to closed-loop output impedance (Zol) is covered in the slides.

Note that the OPA197 Zo is quite flat over a wide frequency range and thus, its Zol will be quite flat over frequency as well.

6740.Op_amps_Trust_but_Verify.pdf

Regards, Thomas

Precision Amplifiers Applications Engineering

0 Michael Steffes over 4 years ago in reply to Raymond Zhang1

Guru 48395 points

I have it simulating, just can't paste the picture - the closed loop Zo is the open loop Zol divided by the 1 + LG term. It is show straight line rising 20dB/dec just like it should with the LG rolling off 20dB/dec