Design And Implementation Of A Low Voltage And High Current BUCK Converter

The BUCK DC-DC converter is important in the area of switching power supply because of its unique step-down advantages and performance advantages.With the rapid development of various communication equipment,digital signal processors,base stations,microprocessors and portable electronic products,the power management chips is required by individuals.The increasing integration makes more functional modules integrated on the same chip.To meet the product requirements,the chip needs lower supply voltage and higher output current,making the design of low-voltage high-current BUCK converter a research hotspot.Based on the application requirements of low input voltage and high output current,and the research of switching power supply theory,a proposed BUCK DC/DC converter is designed in this paper.Considering that the load current in the application is relatively stable and the load current jump is rarely performance,the voltage mode is selected as the control mode of the system.The mode has strong anti-noise ability,relatively simple loop,and high stability.Since the load current is as high as 20 A,the power transistors is designed in the off-chip.In addition,due to the low input voltage,the loop gain is reduced,and the control accuracy of the system is affected.To solve these problems,several internal modules are designed to improve loop gain and accuracy.The bandgap reference which adopts a high-order temperature compensation strategy to ensure the accuracy and reliability is designed in this paper.In order to keep the switching frequency stable,the oscillator circuit designed in this paper utilizes a constant current source charging method and the internal improved structure to achieve precise frequency control.Besides,the PWM comparator and the error amplifier in the chip achieve high performance by the conduction structure.Moreover,a digitally controlled soft-start circuit that can perform a hiccup mode discharge when the chip is overcurrent and continue to charge quickly at the end of the overcurrent to reduce the delay time is designed,to futher improve system performance.Based on the 0.35?m BCD process,the simulation software is used to verify the performance of the bandgap reference circuit,oscillator circuit,error amplifier circuit,PWM comparator circuit and soft start circuit.Finally,the ripple of output voltage and inductor current,load transient response,soft start,and system operating efficiency are verified and analyzed.The simulation results show that the system can operate in the low input voltage range of 2.25~5.5V,the output voltage can be as low as 0.7V,and the maximum load current can reach 20 A.Besides,the the maximum efficiency can reach 97.52% under full load conditions.