Research And Design Of BUCK Converter Loop With Fast Transient Response

With the rapid development of consumer electronic products and integrated circuit industry,power management has been popularized from the original special industry to people's daily life.Among various power management chips,switching power chips have been widely used to supply power for various electronic systems due to their advantages of high efficiency,small size and high reliability.The current mode controlled BUCK converter has become one of the most widely used switching power supply chips due to its advantages such as wide input voltage range,simple compensation mode and better transient response characteristics.This paper based on the current mode control BUCK converter,starting from the modeling of small signal loop,derive the transfer functions of the internal current loop and the voltage loop of the current mode BUCK in detail,and clarify the influence of the loop quality factor on the double poles at half of the switching frequency,as well as the relationship between the slope compensation and the loop quality factor.At the meantime,the gain margin of the current mode loop is used as the upper limit of the design Q value,and the phase margin of the loop is used as the lower limit of the design Q value to obtain the theoretical optimal loop quality factor.In addition,simplis software is used to verify the correctness and predictability of the theoretical analysis,so as to provide theoretical guidance for the design of the adaptive slope compensation circuit.In order to designing a high-performance BUCK converter,this paper starting from the system-level design of the chip,makes clear the selection of the chip's power MOS,off-chip capacitor,inductor,DCR sampling network,frequency compensation network and soft start capacitor step by step.Then this paper also details the key sub circuit design principles and design rules of the fast transient response BUCK converter,which are fixed slope compensation and oscillator circuit,adaptive slope compensation circuit for achieving the optimal Q value control and fast transient response,and I_error transient error correction circuit for correcting the transient error of the chip which is caused by too small input/output voltage difference.In this paper,cadence software was used to build the sub-circuit and loop of the fast transient response BUCK converter,the system's logic,output voltage ripple,linear regulation,load regulation,load transient response time,system transfer efficiency and other key parameters were verified by the integrated circuit simulation.Finally,highprecision power supply,electronic load,oscilloscope and other testing tools have been used to verify the function and performance of BUCK chip.