The Role Of Compensating Feedback Network With Feedforward Capacitor In The Switching Power Supply

With the rapid development of Information Technology, low power DC/DC converter is used widely in computer and communication applications. In order to meet demands for faster and more efficient data processing in these applications, it will require aggressive power management. That is to say, it will require special power supply to provide lower voltages with higher currents and fast transient capabilities, whilst high power density, high efficiency, and high reliability are also desired.For almost Linear and Switch Power Management IC, the negative feedback loop is their heart which keeps the output voltage stable going with the change of input voltage and load. DC/DC converter with internal compensation decrease the external components as less as possible to save the time of design and debug for the designer. However, the simplification confines the designer's capability to optimize the transient response. Fortunately, a feedforward capacitor is still recommended to optimize the loop response. This article not just provides the guideline to select the right feedforward capacitor, but also try to achieve a more adequate bandwidth and phase margin to improve loop stability through measure the transient response of DC/DC converter and use the appropriate feedfoward capacitor.Generally speaking, the switch frequency is constant and the sampled signal are input voltage, output voltage, output current, inductor voltage, inductor peak current which can constitute the single loop or multi feedback loop to keep the system stable. At the same time, they can make something accessory function like over current protection, resistance to slant magnetic and average the current true. In this article, the analysis is focused on the voltage loop control and current loop control for the step-down and step-up converters and the common feature are internal compensation, adjustable output voltage. The feedforward capacitor will be fixed at the divider resistance in order to serve the theory with practice.This content includes the develop process for each of control mode and the role of feedforward capacitor play in them, basic operating principle, detailed circuit schematics and waveform with their application point. Simulation will help to understand them. At last, abundant bench test will verify the calculate and measurment.