Analysis of AC Loading Effects on the Output Voltage Ripple of a Current-Mode Constant On-Time Buck Regulator
Date Issued
2014
Date
2014
Author(s)
Yen, Ming-Chuan
Abstract
In recent years, there have been two technical trends for the DC converters for
powering computer central process units (CPUs). One of the trends is to push up
conversion efficiency not only for the heavy-load condition but also for the light- load
condition. The other trend is to interleave multi-channel converter to achieve high load
current at low voltage output. For the reasons, current-mode (C.M) constant on-time
(COT) control scheme has been widely adopted by industry in recent year.
For CPU power converter applications, the average output voltage is usually
required to provide adaptive voltage position (AVP) feature. The ripple voltage
magnitude must also be keep within tight range, usually in the range of 30 mV, when the
CPU load current is changing with time. To emulate the CPU current, a large
square-wave load current ranging from several kilohertz to megahertz is usually
imposed on the DC converter and tests the output voltage ripple voltage. The focus of
the thesis is to investigate the AC loading effects on output ripple voltage.
In this thesis, a qualitative analysis of the issue is first given using duty-cycle
VI
modulation spectrum theory. This analysis provides insight into the complexity of the
issue. Then a quantitative analysis based on a time-domain approach is used to derive
converter output voltage ripple in terms of the converter load current excitation. A
solution is established for estimating the worst-case output ripple voltage due to
repetitive large-step AC load current excitation of wide-range frequencies. The results
are verified experimentally. A parametric sensitivity analysis for a practical converter is
also provided to give an idea about the sensitivity of each parameter variation on the
overall ripple magnitude. The analytical results obtained, although complicated, are
useful to the designers.
Subjects
電壓調節器
適應性電壓定位
固定導通時間控制
電流模式
輸出電壓漣波
時域方法
調變頻譜理論
Type
thesis
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