The Design Of Digital DC-DC Power Converter With GaN Power Devices

With the booming development of new energy vehicles,electric and intelligent vehicles,the use of on-board electronics is seeing an explosive increment.High efficiency and high reliability power converter is becoming an integral part for the future automotive.This paper utilized GaN power power devices and implemented digital control mode to achieve a 40/5V automotive BUCK converter design.For high conversion ratio BUCK converter,this paper implemented a high reliability digital loop control and designed a high efficiency GaN driver to achieve high conversion ratio and high efficiency.To get accurate transfer function of openloop BUCK topology,the average-modelling method is firstly adopted to analyze the large signal,and a small-signal modelling method is employed from discrete time domain.At the same time,the delay and quantization factor in the control loop are considered to obtain a digital open-loop z-domain transfer function which is close to the real situation.With the help of the simulation compensation method,the s-domain transfer function is obtained by bilinear transformation method and complete the corresponding loop compensation.Subsequently,the discrete compensation function could be acquired and is realized by PID digital filter structure.For high-efficiency GaN driver,three crucial technologies: constant current bootstrap control scheme,nanosecond dead-time control,and high-speed level shifter are employed to achieve stable bootstrap voltage,optimal dead-time delay,and lower-delay driver.The designed driver ensures the stable operation of the GaN devices,and achieve high conversion efficiency.Based on the GaN driver chip independently designed in this project,a 40 V to5V digital control Buck converter is constructed.When the switching frequency is400 k Hz and the load current is converted from 100 m A to 500 m A,the output voltage has an 50 mv overshoot.Besides,the converter has a peak efficiency of 97.37% when the input voltage is 12 V,the output voltage is 5V,and the load current is 0.8A;when the input voltage is 24 V and the load current is 0.9A,the peak efficiency is 96.75%;when the input voltage is 40 V and the load current is 0.9A,the peak efficiency is94.26%.The measured results show that the high-side bootstrap voltage ripple voltage is less than 240 m V,the drive channel delay is less than 30 ns,and the dead time is well controlled.Simulation and measured results show that digital control and GaN power converters behaves high efficiency and high reliability and is suitable for high conversion ratio power supply products.