Research And Design Of A Valley Current Controlled DC/DC BUCK Converter

In recent years,with the electronic science and technology developing rapidly,the portable electric devices,such as intelligent mobile phones,notebook computers and tablet PC,become the daily life necessities and people has higher requirement for their performance.Small size,multi-function and strong performance has become an inevitable trend,and its power supply system directly affects the volume,efficiency,reliability and longevity.Compared with the line regulator power,the switching mode power supply(SMPS)becomes the mainstream power supply products because of its little bulk,high efficiency,low cost and extensive application areas.Served as the core of SMPS,The research of DC/DC converter is becoming a hotspot currently.DC/DC converters are widely used in portable electronic products because they can convert DC voltage flexibly and realize functions such as boost,BUCK,BUCK-boost,and polarity inversion.This paper introduces the background of the research first,and then introduces the theoretical basis of the valley current controlled DC/DC BUCK converter.On this basis,the system architecture and external components selection are discussed and analyzed.Then,based on the HHNEC 0.35?m BCD process,the key modules are designed and simulated.The sub-module circuit includes error amplifier,soft start circuit,current foldback protection circuit,voltage-current conversion circuit,Comparator module and Power Good module.For different sub-module circuit,this paper adopted a number of novel circuit structure to ensure that the circuit has a high performance.For example,the error amplifier adopts asymmetric differential pair as its input terminal based on the Multi-tanh Principle to allow it handle larger voltage swings at its input.Finally,the system performance is simulated by Hspice.The results of simulation show that the performance of the system meets the design requirements.The valley current controlled DC/DC BUCK converter adopts constant on-time modulation,with 5V-28 V wide input voltage and as low as 0.6V output voltage.It means the converter can deliver very low duty factors.Due to the constant on-time and the valley current controlled mode,the error of the previous cycle does not affect the next cycle,so even if the duty ratio is greater than 50%,no sub harmonic oscillation occurs.Therefore,no slope compensation is required.The chip operates at continuous conduction mode for heavy load and forced continuous conduction mode or discontinuous conduction mode for light load to achieve efficiency of up to 93.8%.In addition,the chip also integrates soft-start circuit,current foldback protection,overvoltage protection and undervoltage protection and other protective circuits to improve its reliability.