Converter With External Clock Synchronization Research And Design Of High Current Buck DC/DC

With the rapid development of electricity and electronic technology, DC/DC converter has been applied widely in many electronic equipments and developed in the direction of high efficiency, high frequency and low-power dissipation. Based on the project"Design technique research of mixed-signal IC for single chip"of Key Lab of High-Speed Circuit Design and EMC, Ministry of Education of Xidian University, a high current Buck DC/DC converter with external clock synchronization function is designed.This paper introduces the basic principle of Buck DC/DC converter and studies the control mode. By using the peak current PWM control mode, the transient response ability of the variation of supply voltage and load is improved. Applying a phase-lock loop to the chip realizes the function of synchronizing the switching frequency with the frequency of external clock signal, which is helpful to reduce the interference from other power supplies in the distributed power system. Designing a circuit of pin mutiplexing, external clock signal enters the chip by enable pin which saves a pin for the chip. It improves the convert efficiency and saves the area of PCB by the application of synchronous rectification technique.In addition, many protection circuits are integrated in the chip, such as under voltage protection, over temperature protection, current limit protection, zero crossing detection and so on.Based on 0.35μm 20V BCD process, the whole chip and its sub-modules have been designed and simulated by Cadence. The simulation result indicates that the switch current can achieve 7A, the efficiency is up to 94%, synchronous frequency range is from 300KHz to 2MHz, which meet the design requirements.