Design Of Buck Converter XD1780 With COT Architecture Based On Ripple Compensation

With the rapid development of science and technology,people rely more and more on electronic equipments.Smart wristbands,smart watches and wearable devices are popular among people.Source is an important part of electronic products and how to use it better becomes the focus of attention.For DC-DC buck converter of switching power supply,the load is very easy to change in different environments,and the change of the load current rate also increases,which requires switching power supply chips needing fast transient responses to load changes.In order to meet these requirements,people begin to study the COT(Constant On Time)control mode,which has a fast transient response.Firstly,this paper introduces the research background and current situation of DC-DC converter,and it describes the basic theory of buck DC-DC converter,which contains the topological structure and the control mode.Then,the overall structure and electrical characteristics of the chip XD1780 are analyzed,and the design and simulation of the key sub modules are given.Finally,the whole chip simulation and analysis are given.This paper adopts the control mode of COT architecture,which does not contain the current sampling module and the error amplifier.In order to get the sampling voltage,two resistors are used to produce the partial voltage.This sampling voltage will be used as a feedback voltage to be compared with a reference level,the result of which will decide whether the new conducting period open or not.So it has a fast transient response.In the COT control mode,it is easy to produce subharmonic oscillation by using cheaper ceramic capacitor as a filter capacitor,which results in instability of the system.Compared with the traditional out-chip ripple compensation,this paper puts forward a kind of on-chip ripple compensation.This structure solves the problem that the output voltage ripple produced by equivalent series resistance of the output capacitor is smaller than the output capacitor produced itself with no extra chip pin case,which increases the stability of the system and improves the performance of the chip.DC-DC buck converter XD1780 is designed using 0.18?m BCD process,and the chip is simulated by Spectre tools under Cadence software in this paper.The simulation results of the system show that the chip has a fast transient response,and the response time is 6.8 ?s.When the output voltage is 1.05 V,the output ripple voltage is 7m V.