| Power supply technology is one of the important components of modern information technology.As one of the high and new technologies that modern society generally attaches great importance to and vigorously develops,there is broad development space and market prospects for power supply technology.DC-DC converter is an important branch of power supply,which is widely used in telecommunications and consumer electronics.Research on the high efficiency,low power consumption,high reliability and low cost of DC-DC converters is becoming a hot spot.In this paper,two working modes of continuous conduction and discontinuous conduction of BUCK type DC-DC converter are analyzed.Based on synchronous rectifier technology and PWM modulation,a Buck DC-DC converter with high efficiency under different load conditions is proposed.The circuit design of a highefficiency current mode step-down converter is completed with Cadence software platform and NEC 0.35m 40V BCD process.Input power voltage range is 9-22V,output voltage is 5.2V,maximum load current is 2.5A,and working temperature range is-40～120℃.Six key sub-circuit modules including reference voltage circuit,comparator,error amplifier,oscillator,under-voltage detection and slope compensation are analyzed and simulated.Based on the stability characteristics of Zener diode,the pre-voltage circuit is designed to increase the input range of power supply voltage.In the input voltage range of 9～22V,the pre-regulator circuit provides stable working voltage to the bandgap reference circuit and the linear regulator circuit,and the power rejection ratio(PSRR)of the bandgap reference source is improved.A temperatureindependent output reference voltage is generated by the temperature characteristics of the base-emitter voltage of the triode in the band-gap reference circuit,and the stability of the reference voltage is ensured by the linear voltage regulator with Miller compensation for frequency compensation.In order to meet the requirements of high resolution system and wide range of differential gain,a PWM fast comparator composed of two-stage differential op-amp with the characteristics of noise reduction and drive chain is designed.The gain error amplifier with a folded cascode structure is designed to the recovery potential speed and system transient response rate.An oscillator circuit is designed to provide the clock cycle signal to the converter based on two comparators comparing the reference voltage and the reference voltage of the capacitor.The voltage comparator is used to compare the reference voltage and the sampling voltage of the three sampling resistors and detect the input supply voltage to ensure the converter works in the continuous conduction mode(CCM).The undervoltage detection circuit is designed to ensure the stability of the circuit.A slope compensation circuit with a fixed slope is designed to eliminate the sub-slope oscillation caused by the current control mode,and the stability and conversion efficiency of DC-DC converter are guaranteed.The whole circuit simulation platform was built.the functional simulation and verification of the DC-DC converter overall circuit such as startup,shutdown,steadystate output is completed.It works normally and stably.The input voltage is 9V～22V,the output voltage is 5.2V,the maximum load current is 2.5A,and the maximum conversion efficiency is 92.6%when the load is 0.75A.The overall layout design of the converter is designed.The layout area is 2900um x 2700pm.The results show that the conversion efficiency of the DC-DC converter designed in this paper is high,and there is practical application significance in the fields of electronic equipment,mobile communications,etc. |
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