Design Of DC-DC Buck Converter Based On Improved Voltage Mode COT Control

In recent years,with the development of smart phones,wearable devices,IOT and other portable electronic devices,the research and commercialization of supporting power management products have become a hot spot.At present,portable devices are developing in the direction of miniature and low power consumption,so it has a wide range of application scenarios to design a DC-DC Buck converter for portable electronic products.This paper mainly studies the control mode of Buck DC-DC converter,and introduces the loop stability of voltage mode,current mode,voltage mode COT,current mode COT and V²COT.Then,according to the application requirements of the power management chip of portable electronic products,the architecture of voltage mode COT is selected.This architecture has the characteristics of simple structure,unaffected by oscillator frequency,good transient response,and high light-load efficiency.Based on this,an internal compensation scheme of improved voltage mode COT is proposed in this paper.The scheme uses type II compensation to generate a main pole and a zero of the system.At the same time,the virtual inductor current technology is used to filter the switching node V_SW of the DC-DC converter,and a triangular wave with the same slope as the inductor current is generated.One end of the main comparator of the system is compared with the output of the error amplifier,and a zero point of the system power stage is compensated.Then through the modeling,the design of the peripheral circuit and the compensation circuit,the feasibility of the scheme is verified in the Simplis software.The Simplis simulation results show that the improved voltage mode COT has good stability,and the device parameters have a large adjustment range.The performance is less affected by the equivalent series resistance on the output capacitor,and capacitors with small equivalent series resistance such as ceramic capacitors can be used.In this paper,the 0.13μm BCD technology is used to tape out the DC-DC converter of the improved voltage mode COT.The input voltage of the chip is 3.7-5.5V,the output voltage is 3.3V,the maximum load current is 600m A,and the operating frequency under the CCM steady state is 1.5MHz,the chip can remain stable under heavy load CCM and light load DCM,the startup time is 0.94ms,the linear regulation is 0.03%/V,the load regulation is 0.001%/m A,and the overshoot and undershoot of the load transient response are 48m V and 69m V respectively,meanwhile the output voltage do not oscillate during the process of returning to the steady state,and the stability is good.Finally,by comparing with the same type of chips,it shows that the improved voltage mode COT internal compensation scheme adopted in this paper has good stability,simple design,small chip area of the main loop,simple peripheral devices,and good application value.