Freewheel duration adjustment circuits for charge-control single-inductor dual-output switching converters

Three freewheel duration adjustment circuits based on the principle of phase-lock loop are proposed to enhance the efficiency of single-inductor dual-output (SI-DO) switching converters. The SI-DO converter works in pseudo-continuous conduction mode and uses charge control with a single-charge successive-discharge scheme. The first circuit defines a constant freewheel time (T_FW); the second uses the ratio of charging and discharging currents to define T_FW/T; and the third adjusts T_FW/T according to the load current. The integrated converter is designed using a 0.35μ CMOS process.