THS3491: Phase margin

Takumi Suzuki1

Mastermind 8610 points

Part Number: THS3491
Other Parts Discussed in Thread: TINA-TI

I would like to know the phase margin of THS3491.

As I can not read the value from the datasheet (fig22, 14page) and I am not familiar with current feedback opamp,

let me ask you this question,

Thank you for your support.

Takumi

over 4 years ago

+1 Michael Steffes over 4 years ago

Guru 48395 points

Morning Takumi-san,

Normally, these parts are specified with about 63deg phase margin to give a closed loop Butterworth response. To simulate, follow the step in this article #7 - also, #5 shows some general LG sim info.

https://www.planetanalog.com/stability-issues-for-high-speed-amplifiers-introductory-background-and-improved-analysis-insight-5/

https://www.planetanalog.com/stability-issues-and-resolutions-for-high-speed-current-feedback-op-amps-insight-7/

+1 Michael Steffes over 4 years ago in reply to Michael Steffes

Guru 48395 points

Oh, and I looked to see if I had a THS3491 loop gain sim, yes - here is one - The internal models are slightly different by packages due to package bond wire parasitics, this is a DDA model, Normally you don't do seperate models, but with a part this fast you need to include those effects. The feedback network is set up for a particular app and is overcompensated right now, you adjust it to your needs.

6136.THS3491 DDA 2018 model LG test.TSC

0 Takumi Suzuki1 over 4 years ago in reply to Michael Steffes

Mastermind 8610 points

Hi Michael-san,

Thank you for your kind reply !

Let me study your article.

About the TINA file you gave me, I could not open it, to my regret...

If you have a time, will you tell me something advice.

My TINA-TI version is "9.3.150.328 SF-TI", Japanese version.

Thank you for your support.

Best Regards,

Takumi

+1 Michael Steffes over 4 years ago in reply to Takumi Suzuki1

Guru 48395 points

I had save that LG sim as a V9 file - should have opened for you, here is a V7 version,

5076.THS3491 DDA 2018 model LG test.TSC

0 Takumi Suzuki1 over 4 years ago in reply to Michael Steffes

Mastermind 8610 points

Hi Michael-san,

Thank you for your kindness, I could open the file.

Regards,

Takumi

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THS3491: Phase margin