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Riso with Dual Feedback Op Amp Stability

Riso with Dual Feedback Op Amp Stability. Collin Wells Tim Green Precision Linear Analog Applications November 21, 2013. Riso with Dual FB Topology (OPA330 Example). Zo Test. Zo Test. Modified Aol. Zo and CL. Modified Aol will have Complex Poles with sharp phase shifts anywhere CL

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Riso with Dual Feedback Op Amp Stability

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  1. Riso with Dual FeedbackOp Amp Stability Collin Wells Tim Green Precision Linear Analog Applications November 21, 2013

  2. Riso with Dual FB Topology (OPA330 Example)

  3. Zo Test

  4. Zo Test

  5. Modified Aol

  6. Zo and CL Modified Aol will have Complex Poles with sharp phase shifts anywhere CL Crosses Zo in Zo “Inductive” region.

  7. Modified Aol with CL

  8. Modified Aol with CL

  9. Zo, CL, Riso CL CL CL Riso=400ohms, CL=1uF Series Combination - Highest Z wins - Intersects Zo as Resistive Impedance CL CL Riso Riso Riso Riso Riso Riso

  10. Modified Aol with CL=1uF, Riso=400ohms

  11. Modified Aol with CL=1uF, Riso=400ohms • Note: • Modified Aol looks like an Aol with a second pole around 1kHz and a zero at about 20kHz • No abrupt phase shifts and minimum phase is 29.488 degrees away from 180 degree total phase shift • Modified Aol UGBW=56.5kHz with phase margin at 72.33 degrees

  12. FB#1 with CL=1uF, Riso=400ohms

  13. FB#1 with CL=1uF, Riso=400ohms FB#2 fz2 Net 1/Beta Lowest FB Wins! New fcl • Note: • At fcl, where loop gain goes to zero, there is a 40dB/decade rate-of-closure indicating INSTABILITY for FB#1 alone • We will add FB#2 s shown for a Net 1/Beta which will be stable at new fcl

  14. FB#2 with CL=1uF, Riso=400ohms, RF=100k, CF=82nF

  15. FB#2 with CL=1uF, Riso=400ohms, RF=100k, CF=82nF

  16. Loop Gain for CL=1uF, Riso=400ohms Final Compensation

  17. Loop Gain for CL=1uF, Riso=400ohms Final Compensation Phase Margin

  18. Riso with Dual Feedback curves

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