Output capacitor comparison for low voltage high current applications

The digital IC such as microprocessor requires low voltage, high current as well as very tight transient regulation. This imposes strict requirement for the power supply-typically a step down PWM converters with single phase or multiphase. The output capacitors play an important role in the transient response. Many types of capacitors are available in the market such as aluminum electrolytic, tantalum, POSCAP, OSCON cap, Specialty polymer, as well as large value of multilayer ceramic capacitors. This paper derives a basic equation to calculate the minimum number of capacitors in order to meet the transient requirement. Based on this information, a compromise between cost and performance can be decided by engineers.