Design Of Constant On-time Control BUCK Converter With PLL Synchronization

The power management chip is a key module in electronic devices,and its performance directly determines the quality of electronic devices.Switching power supplies are becoming more and more popular due to their low power consumption,high efficiency,wide application range,and high integration.Constant On Time(COT)control Buck converter has the advantages of good transient response performance and high light load efficiency,which is favored by designers.However,the COT control Buck converter has the shortcomings of switching frequency is subject to working conditions.In this paper,a constant on-time controlled Buck converter based on Phase Locked Loop(PLL)synchronization is designed.Aiming at the problem that the switching frequency of COT control Buck converter is subject to working conditions,the COT control Buck is modeled and analyzed,and the compensation scheme of the system loop is designed.After that,the phase-locked loop of frequency regulation and the phaselocked loop of clock synchronization are designed.The former phase-locked loop can lock the switching frequency of the system to a reference clock frequency,so that the switching frequency of the Buck converter is stable when working stably,thus solving the problems in the conventional COT control.Meanwhile,the bandwidth of the phaselocked loop is designed about one quarter of the loop bandwidth of the Buck converter,which ensures the high transient response speed of the COT control when the transient step,so that the output voltage of the Buck converter can be quickly recovered.It will not be slowed down by the phase-locked loop.The second PLL can synchronize the internal reference clock frequency with the external input clock frequency,which makes it possible to parallelize multiple power chips.It greatly increases the flexibility of power supply schemes and eliminates the Frequency Beating Interference in complex power supply systems.The circuit in this paper is designed based on the 0.35?m BCD process and is simulated and verified under Spectre.The simulation results show that the clock synchronous phase-locked loop can synchronize the internal clock signal with the external clock,and the frequency-controlled phase-locked loop can stably control the switching frequency.And during the load current step 0A to 4A,the output voltage has a maximum overshoot of 83 mV and a recovery time of up to 42?s.During the change of input voltage from 4V to 14 V,the linear adjustment rate of the chip is 0.015%/V.During the change of load current 0A to 4A,the load regulation rate is 0.18%,which meets the design specifications.The test results show that the Buck converter designed in this paper has normal functions,realizes phase-locked loop synchronization function and precision output.In order to improve the load current of the converter,a constant on-time controlled Buck converter controller based on Phase Locked Loop(PLL)modulation is designed,using DCR current sensing mode.The input voltage ranges from 6V to 18 V and the output voltage ranges from 0.6V to 10 V.The level shift circuit and the floating voltage generating circuit are added to DCR current sensing circuit.In order to ensure the correctness of current sensing in wide output voltage range,current sampling circuit has a bandwidth of 9.35 MHz,a gain of 15.4 dB and a common mode input voltage range of 0V~10V.