Comparative studies of common fix-frequency controls for reference tracking and enhancement by end-point prediction

Authors:
Patrick Y. Wu;Philip K. T. Mok
Affiliations:
ViXS Systems Hong Kong Limited, Shatin, Hong Kong and Department of Electronic and Computer Engineering, The Hong Kong University of Science and Technology, Kowloon, Hong Kong;Department of Electronic and Computer Engineering, The Hong Kong University of Science and Technology, Kowloon, Hong Kong
Venue:
IEEE Transactions on Circuits and Systems Part I: Regular Papers
Year:
2010

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Embedded power supply for low-power DSP

IEEE Transactions on Very Large Scale Integration (VLSI) Systems - Special issue on low power electronics and design

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Abstract

This paper analyzes the dynamics of reference tracking in switched-mode power converters in terms of both large-signal and small-signal perspectives. Common control schemes, namely, voltage mode, current mode, and V2-control, are compared for their performance in reference tracking. For small-signal analysis, loop gains and reference-to-output transfer functions are analytically derived and verified by the proposed Matlab-based frequency response simulator. In the case of multiple-loop control like V2-control, different loop gains are clarified for their application in load transient or reference tracking. Practical circuit-level design considerations are given to current-mode control for achieving fast reference tracking, while end-point prediction (EPP) is used to improve V2-control, which is inherently slow in reference tracking. The effect of EPP on transfer function is then explained in details. A V2-controlled buck converter with EPP is fabricated. The measured reference-tracking response shows ten times improvement in tracking speed and verifies the effectiveness of EPP in V2-control.