Research And Design Of Asymmetric Power Distribution Constant Current And Constant Voltage Converter

The rapid development of high power demand for portable mobile devices,modularization and miniaturization are becoming more and more common,and the requirements for power management chips are getting stricter.It is difficult to meet the demand with a single power input in some high power output occasions.It is necessary to parallel the converters to perform asymmetric power distribution on different inputs.Modules in parallel Parallel working of module can improve the output power and the fault tolerance of power systems,and avoid too much current stress on a single converter.The constant current and constant voltage converter not only can realize the output power distribution easily,but also has the advantages of strong load capacity,large input and output range,simple stability design,which has a broad market prospect and application range.The research object of this paper is the constant current and constant voltage buck converter controlled by average current mode Firstly,the topology of Buck DC-DC converter is introduced,analyzes the key variables in CCM,BCM and DCM modes.The advantages and disadvantages of voltage mode control PWM and current mode control PWM are compared,and the average current mode control method is analyzed.The traditional average current mode control uses a current detection amplifier and a current regulation amplifier.The circuit structure and compensation network are complex.In this paper,a current error amplifier and an inductor current programming buffer are used to achieve average current mode control.This mode’s loop compensation is simple and output power is controled precisely.Using the state space averaging method and the switching element averaging method to obtain the small signal transfer function of the converter main circuit,after that,the loop stability is analyzed in combination with the control loop model.The asymmetric power distribution principle of parallel system is derived from the adjustable current limiting function of a single converter.Design and simulation verification of the main modules,including: bandgap voltage reference,current error amplifier,oscillator,inductor current programming buffer and protection circuit.This paper is based on the 0.35μm BCD process and is simulated using Cadence software.The results show that the converter can be started within 1.25 ms under no-load conditions and started within 1.8ms under heavy-load conditions;The constant current and constant voltage function of the converter is normal;The converter can achieve asymmetric power distribution when working in parallel;the conversion efficiency of the converter can reach up to 93%.According to the layout design rules,the circuit layout,wiring,DRC and LVS,and finally the chip layout design is completed.