Research On Adaptive Slope Compensation Technology Of Valley Current Mode COT Control

In recent years,COT-controlled converters have been widely favored due to their fast transient response,high light-load efficiency,and simple control structure.The research in this dissertation takes valley value current-mode COT-controlled Buck converter as an example to solve the problem that the current-mode COT-controlled converter is prone to stability due to the smaller current sampling ripple when multi-phase parallel or high-current applications are used.This dissertation designs a two-phase independent sampling converter to avoid the ripple cancellation effect and introduces adaptive slope compensation to improve the jitter problem of the sampling inductor current becoming smaller.Based on the 0.18μm BCD process,this dissertation designs a dual-channel independently sampled valley current-mode COT-controlled Buck converter.The independent sampling design avoids the ripple cancellation problem of the pulsedistributed multi-phase power supply.The converter designed in this dissertation adopts dual-channel integration and has a higher power density,and can further expand in parallel according to application requirements.This dissertation completes the chip system architecture design,and introduces the system composition and basic working logic.Then the loop compensation scheme of the converter is given,and then the subcircuit is designed and simulated.Finally,layout the chip layout and perform R3 D simulation on the power MOS to determine the wiring resistance.The simulation results show that the chip supports a maximum load current of 3A for a single channel,and supports a dual-channel parallel connection to 6A output.The converter can be synchronized by an external clock and the maximum operating frequency can reach4 MHz.The chip has good transient response capability.Under 1.8V output,when the load current is stepped from 100 mA to 3A,the overshoot and recovery time of the output voltage are 62 mV and 15μs,respectively.When the load current is stepped from 3A to100 mA,the overshoot and recovery time of the output voltage are 60 mV and 12μs,respectively.The chip has protection functions such as overcurrent and overvoltage.In this dissertation,on the basis of valley current mode COT control Buck converter,an adaptive slope compensation circuit is added to improve the jitter problem when the sampling inductor current becomes smaller.The small signal model shows that the fixed compensation slope will introduce a fixed zero and a movable pole,and there is an overcompensation problem under some operating conditions.This dissertation proposes two adaptive slope compensation schemes for over-compensation.The first method of inductor current falling slope tracking(FST)uses the method of tracking the inductor current falling slope to fix the pole,so that the loop compensation design can be more convenient.And by introducing a transient enhancement circuit to improve the load step response.The simulation results show that the compensation slope can better track the inductor current slope,and the added transient enhancement circuit can further improve the load response.When the load jumps from 3A to 100 mA under 5V output,the output voltage overshoot is reduced by 150 mV,and the recovery time is shortened by 10μs.When the load changes from 100 mA to 3A,the output voltage undershoot is reduced by130 mV,and the recovery time is shortened by 12μs.The second delay slope compensation(DSC)scheme introduces a delay control circuit on the basis of the first scheme to achieve the control waveform without slope.The introduction of slope compensation improves the stability while also improving the loop margin.Under the same compensation network and 5V output voltage conditions,when the load current is stepped from 100 mA to 3A,the output voltage undershoot is reduced by 47 mV,and the recovery time is reduced by9μs;when the load current is stepped from 3A to 100 mA,the output voltage overshoot is reduced by 58 mV,the recovery time is reduced by 12μs.The simulation results of the DSC adaptive slope compensation scheme show that the control method has a faster response speed under the same compensation conditions,and has a larger loop bandwidth and phase margin.