High performance CMOS integrated PWM/PFM dual-mode DC-DC buck converter

Abstract

This paper presents a dual-mode CMOS integrated DC-DC buck converter for portable application. The proposed dual-mode buck converter is designed to be controlled by PFM (pulse frequency modulation) and PWM (pulse width modulation) modes. The converter for the application of wide current range and high power efficiency is used to generate the voltage of 0.5–3.0 V with the battery source of 3.3–5.0 V which has the load current range of 30–200 mA. PFM control is applied to obtain high power efficiency when the load-current is low under 50 mA, while PWM is designed to be operated in the higher range of load-current. A ring-type VCO (voltage-controlled oscillator) is used in PFM circuit and provides a variable frequency to correspond to the output current. In PWM control circuit, the combination of sensing current and ramp signal are applied in feedback circuit of converter. The proposed dual-mode DC-DC buck converter is integrated with 0.18 μm CMOS process. Simulation result shows that the converter provides the well-regulated line and load regulations with power efficiency of 80–90%.