Thermal design considerations for voltage regulator modules

With increasing power density being a main goal in VRM designs today, thermal considerations are mounting in importance. A good thermal model of the VRM is therefore necessary to assure its reliability. This paper develops modeling strategies for traces, layers, and components; outlines thermal issues for the PCB and devices; and takes a look at alternate layouts that improve thermal performance without affecting electrical design goals. Effects of airflow, trace representations, and board-to-ambient resistance are addressed since these are the key thermal components. Experimental verification using a 1 MHz 1U non-isolated self-driven VRM is shown to validate the modeling techniques used. These results are then used in conjunction with electrical requirements to develop a PCB trace design guide for VRMs. This guide builds on the outdated IPC-22 21 standard by including more complex conditions bringing it closer to today´s real situations. Accurately determining the optimal trace specifications should improve thermal and electrical performance