SIMO DC-DC Converter with Low-Complexity Hybrid Comparator-Charge Control

A hybrid control method using a comparator and a charge control method is proposed for a single-inductor multiple-output (SIMO) DC-DC converter. SIMO DC-DC converters have the weaknesses relating to cross-regulation, as all the output channels share the energy stored in a single inductor. Although multiple control methods such as Time-Multiplexing Control (TMC) and Ordered Power Distributing Control (OPDC) have been proposed to prevent cross-regulation or to improve load capability, effective use of limited resources appears to have not yet been achieved. This paper introduces a hybrid control topology that (1) utilizes comparator-based regulations for most outputs and (2) uses a new charge control loop method for the last output to reduce cross-regulation with low hardware complexity. In addition, the proposed scheme efficiently reuses the system's redundant energy by adaptively controlling the freewheeling switch that opens the path to the input battery to store the surplus energy resources again. The proposed SIMO DC-DC converter was designed and validated with a 0.18 mu m 3.3 V CMOS process. The converter has four regulated outputs of 0.9, 1.2, 1.5, and 2.2 V, and as a result of the simulation, it was found that the cross-regulation was estimated to be 0.4 mV/mA when the output current changes by ~200 mA. In addition, estimated peak power conversion efficiency of 88.5% was achieved at a total output power of 405 mW.