1 Introduction

Peak current mode (PCM) control is widely used in buck converters due to the advantages such as good dynamic performance and easy compensation. By using internal compensation with PCM control, the TPS62933 device further reduces the customer-application BOM, which helps to reduce the solution size and design complexity. For common applications, components are selected based on the recommended table and design applications are quickly implemented⁽¹⁾. Methods for choosing output capacitors in applications with large output capacitors are detailed in Stability Analysis and Design of Internally-Compensated Peak Current Mode TPS62933 - Part I: How to Select the Output Capacitor.

However, from the results derived in Part I: How to Select the Output Capacitor, the maximum output capacitance value under the stability constraint is inversely proportional to the output voltage, which makes it difficult to select a large capacitance in high output voltage applications. This difficulty leads to the contradiction between voltage ripple, voltage noise, and a stable design. This document first explains the root cause of the contradiction based on theoretical analysis. Then the effects of feedforward capacitor C_ff on the loop are introduced. With a pair of introduced zero and pole in the loop, the phase margin can be improved for stability, which enlarges the range of output capacitance selection in high output voltage applications.