Modeling of a Constant On-Time Current-Mode Control Scheme with Offset-Correction and Adaptive Voltage Positioning Functions for Voltage Regulators
Date Issued
2012
Date
2012
Author(s)
Chen, Yung-Jen
Abstract
Voltage regulators have been widely used in many computer applications for powering the central processing units (CPU). Converter efficiency has always been a design priority but most emphasis had been placed on the efficiency under the heavy-load conditions until recent years. Considering the fact that most of the DC converters are operating under light-load or standby conditions most of the time, the total energy loss is significant especially considering the number of computers used today.
To meet the challenges described above, constant on-time (COT) control scheme has received much attention by industry recently. COT control scheme features improved light-load efficiency while preserving heavy-load efficiency. There are various of constant on-time control schemes. The focus of the present thesis is on the current-mode COT scheme (COTCM) applied to a buck converter with adaptive voltage positioning (AVP) feature. Current mode control is considered because it features inherent channel current balancing. AVP is considered because that’s the feature imposed by computer chip maker INTEL Corp. for the purpose of energy saving.
In this thesis, the focus of investigation is on the circuit feedback stability and the converter output impedance which is an important consideration to achieve AVP function. A small-signal model is developed based on describing-function approach which is complicated but necessary to uncover the inherent nature of this control scheme. Experimental results will be shown. A comparison with other COT control schemes will also be given.
Subjects
Voltage Regulator (VR)
Adaptive Voltage Position (AVP)
Constant on-time control
Current mode control
Output impedance
Describing Function
Stability criteria
Type
thesis
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