Comparison of Small Signal Characteristics in Current Mode Control Schemes for Point-of-Load Buck Converter Applications

Different current mode controls have been widely adopted in commercial pulsewidth modulation controllers for point-of-load (POL) converter applications. To understand the unique properties of various current mode control schemes, and to study the differences between them, this paper investigates and compares four current mode control schemes (peak-current control, valley-current control, constant on-time control, and constant off-time control) for POL power converters and voltage regulator applications. Performance attributes under investigation include high-bandwidth voltage loop design, adaptability to a converter with a wide input voltage range, adaptive voltage positioning design, and audio susceptibility. The pros and cons of these schemes are identified and explained by the unified small signal equivalent circuit model. In terms of dynamic performance, this study provides a current mode control scheme selection criteria and feedback design guidelines. The theoretical analyses are verified by both simulation and experimental results.