Understanding Op Amp Dynamic Response In A Type-2 Compensator (Part 2): The Two Poles

Focus:

Part 1 of this article showed the impact of the operational amplifier open-loop gain on the response of a type-2 compensator. Pushing the analysis further, a closer look at the magnitude and phase response of an op amp reveals the presence of two poles—one low frequency and one high frequency. This second part shows how to determine the transfer function of the type-2 compensator accounting for these poles and how they distort the response of the filter, especially the phase characteristics of the compensator. Fortunately, these distortions can be minimized by appropriate selection of the op amp and this article presents a method for doing so. Finally, the more-complete transfer function for the type-2 compensator is applied in a design example consisting of a high-frequency, current-mode-controlled buck converter.

What you’ll learn:

• How to understand the impact of an op amp’s two poles on the response of power supply compensation circuits
• How to derive a transfer function for a type 2 compensator that accounts for the open-loop gain and two poles of the op amp
• How to design a type 2 compensator for high bandwidth applications

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Author & Publication:

Christophe Basso, ON Semiconductor, Toulouse, France, How2Power Today, Feb 17 2017

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