Control of high-step down voltage converters for voltage regulator modules

New technologies are requiring high step-down conversion voltages. A possible solution to this problem is to use several buck converters connected in cascade; however, a complex control circuitry is required. An alternative solution is to use an n-stage positive output cascade buck converter with a single active switch. This class of converters is suitable for VRM applications where low voltages and high currents are required. A controller design methodology for this class of converters is developed using average current-mode control. The proposed scheme employs the inductor current of the input stage and the capacitor voltage of the output stage; therefore, the full benefits of current-mode control are maintained. Experimental results are given for a 80 W switching regulator where the robustness of the proposed controller is tested under changes on the output load.