Low-power Error Amplifier Design Based On Current Mode BUCK Switching Power Supply

Switching power supply has many advantages,such as wide voltage range,miniaturization,high efficiency and so on,so it is widely used in various electronic products in many fields.Especially in recent years,due to the wide application of the portable electronic devices,the design of switching power supply is facing many new challenges,and the performance requirements for the stability and low power consumption have become more important.As the core circuit of the switching power supply,the gain and bandwidth characteristics of the error amplifier directly affect the dynamic characteristics of the whole system,such as load adjustment and response speed.Therefore,the design of high performance and low power consumption error amplifier plays a crucial role in switching power supply circuits.In this paper,a low power error amplifier is designed based on 0.5?m BCD technology for current-mode controlled BUCK switching power supply.The main contents of this paper are as follows:Firstly,some concepts,development history,domestic and foreign development status and future direction of the switch power supply are briefly introduced.Secondly,the structure and working principle of BUCK type circuit,voltage mode and current mode are analyzed.Thirdly,on the basis of the theoretical analysis,the design of the error amplifier circuit is completed according to the design requirements of the system,and a concrete transistor-level circuit structure that accords with the design index is proposed.And the error amplifier core circuit,clamp circuit,bias circuit,soft start function circuit,the internal and external compensation circuit and hysteresis comparator are analyzed in detail.Fourthly,several important indexes of the error amplifier are simulated by Cadence Spectre simulation software.Fifthly,some problems in layout design are analyzed and the circuit layout of the low power error amplifier is drawn based on 0.5?m BCD process.Sixthly,Summarizes all the work and some deficiencies of the paper.Circuit performance was simulated at different process corners,the simulation results show that the open loop gain of the error amplifier is 56.35dB~59.89dB,the unit gain bandwidth is 8.62MH_Z~13.56MH_Z,the phase margin is 52.4°~74.5°,the settling time is 29.7ns~44.5ns,the slew rate is around 3V/?s~3.38V/?s,the common-mode suppression ratio is 94.21dB~127dB,the power supply voltage rejection ratio is60.28dB~67.23dB,and the power consumption is 48.18?W~53.46?W with 3.3V power supply.And the performance of the proposed circuit is consistent with the system requirements.In the whole design process,the error amplifier circuit designed has the following characteristics:1.In the process of designing the error amplifier,some input tubes are designed to work in the sub-threshold region,and the low power consumption of the circuit is realized.2.Two compensation structures,which are internal compensation and external compensation,are designed.In practical application,suitable compensation structure can be chosen according to the requirement of system stability of different equipment.Under normal conditions,the internal compensation can satisfy the stability requirement of the system,and the internal compensation can save the area relative to the external compensation.Therefore,the internal compensation is preferred.However,when the system stability and gain of the system are higher,the internal compensation can't meet the requirements.At this time,the external compensation structure is used.