OPA333-Q1: Phase Margin Gain Margin

Nishant Gupta

Intellectual 340 points

Part Number: OPA333-Q1
Other Parts Discussed in Thread: TINA-TI, INA333-Q1

Subject: Help Required: Phase Margin and Gain Margin Analysis of Op-Amp Current Source

Hello TI Team,

I am evaluating an op-amp-based voltage-to-current source for my system and would like to verify its stability.

Could you please help me with:

How to measure phase margin and gain margin in TINA-TI, including the correct loop-gain simulation setup and interpretation of the Bode plot.
How to perform the corresponding hardware stability measurement without a Frequency Response Analyzer/Bode plot analyzer. I would like to know a practical method using equipment such as an oscilloscope/function generator.
Please suggest easy-to-understand TI literature/application notes for this analysis.
If possible, could you please provide or modify a TINA-TI simulation file for my exact current-source circuit so I can understand the complete procedure?

My circuit is a voltage-to-current source for a constant-current application. The current-source schematic is attached.

Ron Michallick , you previously helped me with a similar simulation in my earlier E2E post. Ron, could you please help me complete the stability analysis for this updated circuit in this new thread? circuit is same

Thank you for your support.

11 days ago

0 Nishant Gupta 11 days ago

Intellectual 340 points

Hello Amplifier of Vcc 5V I have taken INA333-Q1 ...

0 Nishant Gupta 11 days ago in reply to Nishant Gupta

Intellectual 340 points

0 Nishant Gupta 11 days ago in reply to Nishant Gupta

Intellectual 340 points

Please share TINA TI spice file all stability as well as schematic file. Please do and tell what bandwidth i will get and what best phase margin & Gain Margin i can have. Stability with analysis I need .What best i can do in hardware for this evaluation as input is temperature signla which changes at around 1-4 sec with voltage across Veb of BCY70 PNP transitor is range of 0.5- 1.4V

0 Marek Lis 11 days ago in reply to Nishant Gupta

TI__Guru 74561 points

Nishta,

To answer your question, below is the setup for determining phase and gain margins.

The phase margin is determined at the intersection of AOL and 1/beta by looking at the phase of the Loop Gain (AOL*Beta) at said intersection - it shows 58.6 degrees.

The gain margin is determined by looking at the AOL where phase has shifted by 180 degrees - it shows gain margin of 14.1dB - see below.

For more details and understanding, you NEED to review stability analysis training material under the following link: Precision labs series: Op amps | TI.com section (9).

Having said that, typically one wants to use the reference current in other part of the circuit, and your setup does not seem to allow it - see below on the right how this is usually done, including multiplication of the reference current, by scaling of the size of the mirror transistor.

OPA333 100uA Iref AC Stability.TSC

OPA333 100uA reference current.TSC

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OPA333-Q1: Phase Margin Gain Margin