A 48-V Wide- $V_{\rm in}$ 9–25-MHz Resonant DC–DC Converter

This paper presents a wide-V
_in
step-down parallel-resonant converter (PRC), comprising an integrated 5-bit capacitor array and a 300-nH resonant coil, placed in parallel to a conventional buck converter. Soft-switching resonant converters are beneficial for high-V
_in
multi-MHz converters to reduce dominant switching losses, enabling higher switching frequencies. The output filter inductor is optimized based on an empirical study of available inductors. The study shows that faster switching significantly reduces not only the inductor value but also volume, price, and even the inductor losses. In addition, unlike conventional resonant concepts, soft-switching control as part of the proposed PRC eliminates input voltage-dependent losses over a wide operating range, resulting in 76.3% peak efficiency. At V
_in
= 48 V, a loss reduction of 35% is achieved compared with the conventional buck converter. Adjusting an integrated capacitor array, and selecting the number of oscillation periods, keeps the switching frequency within a narrow range. This ensures high efficiency across a wide range of V
_in
= 12-48 V, 100-500-mA load, and 5-V output at up to 25-MHz switching frequency. Thanks to the low output current ripple, the output capacitor can be as small as 50 nF.