This paper designed a buck DC-DC converter chip based on SMIC 0.35μm BCD process,which is mainly used in high-power and wide-input power management systems.In this paper,the peak current type PWM control method was used to provide excelle nt load regulation characteristics and resistance to input power disturbance;slope comp ensation was added to the output of the current sampling to eliminate the sub-harmonic oscil lation caused by the peak current mode;this paper designed a high-gain,wide-bandwidth volt age feedback error amplifier to provide large load regulation and load transient response cap ability;the PWM controller with high unity gain bandwidth was designed to meet the requireme nts of high switching frequency operation and improve the conversion efficiency.In add ition,this design added a series of protection modules to maintain the normal operation of the chip.The simulation results show that:this design stably outputs 5.5V voltage within the input voltage range of 10-40V,the switching frequency is 330kHz,the rated output current is 1.5A,and the conversion efficiency in the input range is above 80%.The conversion effici ency up to 90% in typical application.