Cot Controlled Buck Converter
ABSTRACT
The effect of equivalent series resistance (ESR) of an output capacitor on the performance of a constant -on-time(COT)-controlled buck converter is studied and a pulse bursting phenomenon is revealed. It indicates that the ESR of the output capacitor is one of the key factors causing pulse bursting phenomenon in COT-controlled buck converters, and the critical ESR is derived via. It is pointed out that , when the ESR of the output capacitor is smaller than the critical ESR ,pulse bursting phenomenon occurs, otherwise it disappears. Simulation results are provided to verify the theoretical analysis results.
INTRODUCTION
The control techniques of switching dc-dc converters can be generally divided into the following three ways. 1) Constant –frequency control ,such as pulsewidth –modulation-based voltage-mode control and current- mode control 2) Variable-frequency control ,such as output-voltage-ripple-based control like constant-on-time (COT) control or constant-off-time control 3) Hybrid control
To improve the transient performance and to simplify the controller design of switching dc-dc converters, COT control has attracted much attention recently.COT control is simple to implement and easy to design, without an error amplifier and its corresponding compensation network.
In this paper , pulse bursting phenomenon of a COT-controlled buck converter is revealed via both time and s-domain analysis, the ESR of the output capacitor for the pulse bursting phenomenon is obtained. Simulation results are provided to verify the theoretical analysis.
PULSE BURSTING PHENOMENON A) Review of COT Control
COT controller consisting of a comparator, an Reset-Set(RS) trigger, and an ON timer.
From the wave forms, once the output voltage Vo decreases to the reference voltage Vref , the RS trigger will be triggered to turn on the power switch S to increase Vo, after the preset COT interval Ton , the RS trigger will be reset
The effect of equivalent series resistance (ESR) of an output capacitor on the performance of a constant -on-time(COT)-controlled buck converter is studied and a pulse bursting phenomenon is revealed. It indicates that the ESR of the output capacitor is one of the key factors causing pulse bursting phenomenon in COT-controlled buck converters, and the critical ESR is derived via. It is pointed out that , when the ESR of the output capacitor is smaller than the critical ESR ,pulse bursting phenomenon occurs, otherwise it disappears. Simulation results are provided to verify the theoretical analysis results.
INTRODUCTION
The control techniques of switching dc-dc converters can be generally divided into the following three ways. 1) Constant –frequency control ,such as pulsewidth –modulation-based voltage-mode control and current- mode control 2) Variable-frequency control ,such as output-voltage-ripple-based control like constant-on-time (COT) control or constant-off-time control 3) Hybrid control
To improve the transient performance and to simplify the controller design of switching dc-dc converters, COT control has attracted much attention recently.COT control is simple to implement and easy to design, without an error amplifier and its corresponding compensation network.
In this paper , pulse bursting phenomenon of a COT-controlled buck converter is revealed via both time and s-domain analysis, the ESR of the output capacitor for the pulse bursting phenomenon is obtained. Simulation results are provided to verify the theoretical analysis.
PULSE BURSTING PHENOMENON A) Review of COT Control
COT controller consisting of a comparator, an Reset-Set(RS) trigger, and an ON timer.
From the wave forms, once the output voltage Vo decreases to the reference voltage Vref , the RS trigger will be triggered to turn on the power switch S to increase Vo, after the preset COT interval Ton , the RS trigger will be reset
References: 1] E.Figueres ,G.Garcera,J.M.Benavent,M.Pascual,and J.A.Martinez,”Adaptive two- loop voltage mode control of dc-dc switching converters,”IEEE Trans.Ind.Electron.,vol.53,no.1,pp.239-253,Feb.2006. 2]Y-S Lai and C-A Yeh,” Predictive digital- controlled converter with peak-current-mode control and leading edge modulation,” IEEE Trans.Ind.Electron.,vol.56,no.6,pp.1854-1863,jun 2009. 3]Analysis of pulse bursting phenomenon in COT controlled buck converter, IEEE Trans.Ind.Electron,vol58 ,No 12,.dec 2011