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Small-Signal Analysis and Design of Constant Frequency V2 Peak Control (1)

Fig. 1. Constant Frequency V2 Peak Control.
Constant frequency V2 peak control is widely researched in literature and used in industry in DC-DC converters due to its simple implementation and fast transient response. However, the effect of the capacitor voltage feedback needs to be clarified for design purposes. This nugget analyzes the small-signal model for constant frequency V2 peak control. There are two pairs of double poles located at ½ fsw in this control structure because of two kinds of feedback information. First, the sidebands of the inductor current information cause a sample-and-hold effect resulting in one pair of double poles located at ½ fsw. Next, the sidebands of the capacitor voltage information cause another pair of double poles located also at ½ fsw. The Instability issue occurs not only in a large duty cycle case, but also in the case with small capacitor time constants.


Fig. 2. Separation of Feedback Infomation.
Fig. 3. Two pairs of double poles caused by current and cap voltage feedback.



Fig. 4. Stability Criterion.
Fig. 5. Design Considerations for different types of capacitors.
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