Analyses of the impact of current load change on a current-mode constant on-time buck converter regulator

For recent energy-saving computer power converter products, it´s required to provide a very tightly regulated voltage under very stringent current load change conditions. In this paper, this issue is dealt with for a current-mode constant on-time buck converter. An issue about beat frequency effects analysis is first given using modulation spectrum theory and small-signal frequency-domain model. This analysis provides insight into the complexity of the issue. Then a time-domain approach is used to derive converter output voltage ripple in terms of converter load current excitation. The results are verified in experiments. A mathematical solution is established for estimating the worst-case output ripple voltage due to repetitive large-step AC load current excitation of wide-range frequencies.