Input filter interactions in peak-current-mode-controlled buck converter operating in CICM

Peak-current-mode (PCM) control is a widely used method to control switched-mode converters. Most often an input filter is necessary to meet electromagnetic interference requirements. The input filter can cause instability and degradation of input and output dynamics if not properly designed. The input filter design from the output dynamics viewpoint has been addressed in numerous papers, resulting in well-agreed results in the case of direct duty-ratio control. The same methods and criteria have also been applied to PCM control, but the results have turned out to be conflicting. This paper shows that the adverse effect of the input filter on the output performance of a peak-current-controlled buck converter in continuous inductor-current mode is insignificant. The input performance is, however, significantly affected, necessitating the use of proper damping. It is also shown that the instability is caused solely by the instability of the input filter under negative incremental resistance. The methods used are unified in nature, but the results obtained in this study cannot be generalized to be valid for types of converters other than a buck converter.