Application of nonlinear optimization to the study of frequency response characteristics of a voltage-mode regulated DC-DC switching converter

Design of a switching power supply regulator loop requires proper assessment of the impact of component value variations upon the loop gain characteristics. Worst-case phase margin is one piece of information a designer can use to assess whether the converter is properly regulated for given component value variations. Small signal models are used to determine the frequency response data needed for determining the converter loop´s phase margin but they do not accurately predict the converter´s dynamic behavior at higher frequencies where the phase margin is to be determined. In this paper, we propose a novel approach to finding the worst case phase margin of a DC-DC converter. This approach instead of a model uses the steady-state analysis capabilities of the software tool SUPRA coupled with fast Fourier analysis in order to obtain more reliable frequency response characteristics. The complexity of determining the loop gain frequency response is reduced using a two-stage approach. The open-loop control-to-output frequency response is determined through the steady-state analysis method and the frequency response of the regulator is determined analytically. The search of the combination of component values providing the worst case phase margin is done using optimization