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With ideal feedback there is a minus 180° phase shift of negative feedback. At the origin there is usually a pole, so the designer is rolling off to gain at the origin. There cannot be infinite gain for infinite frequency, so there is an initial 90° phase shift, and then, the other components in the system that will cause additional phase shift. The amount of phase that is left between an oscillating system with positive feedback, and the negative feedback system is called the phase margin. Now in switching regulators and in the Power Architect software, anything less than 45° would be considered a weak design, and actions should be taken to improve it. With phase margin a good guideline to look at, is if the transit response has no oscillation in it, then that means it is probably better than 52° of phase margin or critically damped.
