Design Of Buck DC/DC Converter

Single-chip switching power supply management integrated circuits (PSMICs) have many virtues such as high integration level, most cost effective, lowest component count switcher solution, and high performance. As adapted by the demand of portable applications, integrated switching power supp1ies have been widely used in computers, communication systems and consumer electronics, etc. A buck DC-DC converter which can be used in portable electronic products has been designed.The basic principle and system structure in buck DC-DC converter were introduced. And the small-signal models for the switching converters with current-mode PWM control were deduced. Stability and the principle of slope compensation used to improve stability were also discussed. Then a new type buck based on current-mode PWM control was designed. Some advanced techniques, such as synchronous rectifying, soft-switching and pulse width/frequency modulation, were used in the design, which can effectively decrease switching-loss and greatly increase the converter's conversion efficiency.In the practical design, with 0.5μmCMOS process, using tools of Cadence EDA, the main sub-circuits in the system were carefully designed, simulated and analyzed including voltage reference circuit, error amplifier, OSC generator, PWM comparator, Soft activation circuit, pulse width/frequency automatic switching modulation. At last, based on the step-down DC-DC converter with synchronous rectification, curcuit parameters and selection of electronic devices were studied. According to the results of Spectre simulation, the system is stable and the performance specifications required are attained.