A Study on Loop Gain Measurement Method Using Output Impedance in DC-DC Buck Converter

Nobukazu TSUKIJI  Yasunori KOBORI  Haruo KOBAYASHI  

Publication
IEICE TRANSACTIONS on Communications   Vol.E101-B   No.9   pp.1940-1948
Publication Date: 2018/09/01
Online ISSN: 1745-1345
DOI: 10.1587/transcom.2017EBP3358
Type of Manuscript: PAPER
Category: Energy in Electronics Communications
Keyword: 
loop gain measurement,  stability evaluation,  stability of negative feedback system,  phase margin,  dc-dc buck converter,  

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Summary: 
We propose a method to derive the loop gain from the open-loop and closed-loop output impedances in a dc-dc buck converter with voltage mode and current mode controls. This enables the loop gain to be measured without injecting a signal into the feedback loop, i.e. without breaking the feedback loop; hence the proposed method can be applied to the control circuits implemented on an IC. Our simulation and experiment show that the loop gain determined by the proposed method closely matches that yielded by the conventional method, which has to break the feedback loop. These results confirm that the proposed method can accurately estimate the phase margin.