VRM transient analysis at fast load change and fast-transient response with LILC

Abstract

The power supplies with lower output voltage, higher output current and extremely fast load current transients impose severe issues to the design of voltage regulation modules (VRMs). In this paper analyze the effect of the parasitic elements of the output filter capacitor, to the output voltage and the load current slew rate of the switching power supply at the fast load transient. We found that the under-shoot of the output voltage in the sudden load change is not varied with the types of output filter capacitor (not depends of ESR, ESL and C). The output voltage drop in recovery is varied remarkably with the ESR of the capacitor and the load current slew rate is greatly varied with the ESL of the capacitor. The comparing three kinds of output filter capacitors; electrolytic, OS-CON and LILC (low-impedance line component), it realized that newly developed LILC significantly improved the transient response of voltage regulator module. The LILC is a newly developed capacitive component with very low impedance even at high frequencies. Simulation and experimental results are presented to verify the analysis.