Optimized phase positioning for minimizing input filter requirements in single-input multiple-output DC-DC switch-mode power supplies

An input filter is usually required in a power supply system in order to comply with regulations, reduce EMI, and ensure that input transients are properly handled. In systems with a single input power supply and multiple output converters, the phase positioning of the converters affects the input current/voltage ripple as well as the magnitude of the input harmonics. Optimizing the phase positioning of each converter can reduce the required size of the input filter capacitor, in turn reducing cost and physical dimensions. An algorithm is presented for selecting the optimal phase positioning based on each converter parameters and operating conditions. This method is verified using the Exar´s XRP7724 4-channel controller and 4 buck converters.