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V 2 control is a popular control architecture in point-of-load Buck converters due to its simplicity and fast transient response. V 2 control with ceramic capacitor has instability issue. This paper reviews the existing solutions and their limitations are studied. A solution using output capacitor current ramp to stabilize the control loop is proposed. The analog capacitor current sensing method based on impedance match is used in the implementation of lossless current sensing. A small signal equivalent circuit is proposed for the analysis of the proposed control method. The proposed solution is superior to existing compensation methods for the excellent transient response for a wide range of duty cycle. The effectiveness of the concept and implementation are verified by experimental results.

V 2 control has advantages of simple implementation and fast transient response and is widely used in industry for Point-of-Load applications. This control scheme is elegant when output capacitors with large RC time constant are employed, such as OSCON capacitors. However, in most cases using capacitors with small RC time constant, such as ceramic capacitors, instability problem will occur. Previous modeling methods including sampled-data modeling, discrete-time analysis, time-domain analysis and describing function are all very mathematical and difficult to apply for practical engineers as little physical insight can be extracted. Up to now, no equivalent circuit model is proposed which is able to predict instability issue and serve as a useful design tool for V 2 control. This paper proposes a unified equivalent circuit model which is applicable to all types of capacitors by considering the effect of capacitor voltage ripple. The equivalent circuit provides physical insight of V 2 control as a non-ideal voltage source, a dual concept of previous non-ideal current source for current mode control. The equivalent circuit model is a simple yet accurate, complete model and is very helpful for design purpose. Optimal design guidelines for point-of-load applications are provided. The proposed equivalent circuit model is applicable to both variable frequency modulation and constant frequency modulation. The equivalent circuit model and design guidelines are verified with Simplis simulation and experimental results.Index Terms---Equivalent circuit model, V 2 control, ripplebased control, enhanced V 2 control and optimal design guidelines. d vo Driver iL RCo Co RL Ls Pulse Width Modulator vc V ref Hv Vin + -

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