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LM4562: Oscillation possibility

Katsuya Sato
Prodigy 95 points

Part Number: LM4562

Hi, Experts,

I will use LM4562 as a voltage follower as proposed at the next thread I asked the question in.
This is used for a circuit [next image] with up to 20MHz AC input/output, and I simulated to confirm whether or not oscillation occurs.

Thread:
https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/1270592/searching-operational-amplifer-meeting--24v-input-output/4814583#4814583

The circuit [LM4562_Test.TSC] it used at:

About oscillation, I have two questions.

Q1:
I simulated for the circuit to check loop gain: [LM4562_LoopGain1.TSC]. Dose the oscillation not occur?

Q2:

Is the following correct for the condition of no oscillation?
"The loop gain is less than 0 dB when the phase turns 180 degrees."

Thanks,


Katsuya

LM4562_LoopGain1.TSCLM4562_Test.TSC

  • 0
    TI__Mastermind 22260 points

    Hi Katsuya,

    I was able to run a stability simulation with the circuit you attached, and the circuit is stable with a phase margin of around 74 degrees. I attached the file below. As to your second question, the condition where instability occurs is when the loop gain is 0dB and the phase between the inputs are 180 degrees out of phase and therefore have a phase margin of 0 degrees. We have a great video set that covers many useful topics relating to op amps that is worth looking into as it has plenty of examples and tips. The set can be found here, and the topic about stability can be found halfway down the page.

    Best Regards,

    Ignacio