Design Of A Buck DC/DC Chip With Synchronous Constant On Time Control

With the rapid development of electronic technology, power management has been applied in many fields such as automobile, network communications, industrial applications,computer and so on. It has greatly promoted the innovation and research of power supply.With the increasing requirements of people on the performance of electronic products, high efficiency, high load current and high integration are the main development direction of power management chip. Switch mode current loop DC/DC converter has advantages of high conversion efficiency, high load carrying capacity, high integration degree, fast transient response and so on,the application prospect is very broad.In this paper, the current loop synchronous buck DC/DC converter is used as the research object, and the high efficiency and fast transient response is analyzed. Based on the guarantee system voltage loop and current loop stability, a synchronous high voltage current loop constant on time control buck DC/DC converter is designed.The converter has a wide input range of 850 k Hz, the typical operating frequency of 4.5V-26 V, the highest10 A, the output current of 12 A, and the chip can be connected in parallel to provide maximum 20 A output current. The output voltage range of the chip is 0.6V-5V, with 1.2%of the output voltage regulator, and in the same time to ensure the stability of the system, to achieve the ultra fast transient response, the dynamic load step is the maximum of the maximum of only 25μs.The chip uses a synchronous logic control to provide FCCM and DCM two kinds of light load control mode, to improve the efficiency of the chip, the maximum chip efficiency of 94%.The chip provides programmable soft start function,input over current protection, input under voltage protection, output over-voltage protection, over temperature protection, short circuit protection function, in order to ensure that the chip can work safely and reliably in bad environment.Chip characteristics for the synchronous current loop constant on time control. Synchronous zero crossing detection technology and light load DCM mode, to further improve the chip conversion efficiency.Constant on time control with the valley current mode sampling, to overcome the traditional current loop constant frequency control the defects of the slope compensation technology needs, improve the chip transient response speed and chip load capability.At first, the paper introduces the research background and research significance and the power management chip are briefly introduced, then system elaborated the basic principle of the buck DC/DC converter, detailed analysis and the current loop of Buck DC/DC converter, the stability and chip peripheral devices selection, chip steady conversion efficiency, then introduces the chip XD1576 the system design of index are extremely electric properties, and a detailed analysis of the chip of several key modules,the chip was given at the end of the whole simulation waveform, and has carried on the analysis.Chip XD1576 adopting Hua Hong BCD350 GE process model, based on the cadence software platform, using the Spectre simulation software of the chip of each sub module are design and simulation, and the overall function of the chip under different temperature different process corners of the simulation and verification. The XD1576 chip has been taped out.