Improving light load efficiency in a series capacitor buck converter by uneven phase interleaving

This paper introduces a technique to improve light load efficiency in a two-phase, series capacitor buck converter. A unique aspect of the series capacitor buck topology is that if conventional, even phase interleaving is used in discontinuous current mode (DCM), negative inductor current can be generated in one of the phases. The negative current increases power loss and creates an unwanted offset in the series capacitor voltage. Uneven phase interleaving avoids this by overlapping the high side switch on-time of one phase with the positive, decreasing current interval of the other phase. Experimental results from a 12 V input, 1.8 V output hardware prototype demonstrate that this simple technique increases light load efficiency by up to 13 percentage points and reduces power loss by up to 42% as compared to forced continuous conduction mode and conventional, frequency modulated DCM.