12.6 90% Peak efficiency single-inductor-multiple-output DC-DC buck converter with output independent gate drive control

Single-inductor multiple-output (SIMO) DC-DC buck converters, which possess the advantage of compact size, are commonly implemented in portable electronics like mobile phones and tablets. However, their power efficiency is degraded considerably, as illustrated in Fig. 12.6.1, when multiple outputs are requested in a wide range, such as 1.2 to 3.3V for tablets. The use of P-MOSFET [1][2] and N-MOSFET [3] switches results in low efficiency of 64 and 70% at outputs of 1.2 and 3.3V, respectively, because of low gate driving voltages and large on-resistance. This implies that conventional usage of P-MOSFET and N-MOSFET switches is inappropriate in SIMO converters [1-3]. This paper presents a SIMO converter with output-independent gate drive (OIGD) control for all N-MOSFET switches. One of the salient features is that OIGD control achieves output-voltage-independent characteristics on efficiency and keeps peak efficiency of 90% over the range of 1.2 to 3.3V for tablets. The other salient feature is that a low-power deadtime overstress recycling (DOR) technique retrieves 95% of energy loss during deadtime and releases the overstress problem simultaneously.