Workbench Study Concerning the Highest Reliability Outcome for PoL Converters with Different Output Capacitor Technologies

Abstract

The last decade’s studies show that the PoL (point-of-load) converter’s output capacitor is an important component for reliability, implying that its careful selection may determine the overall converter’s failure rate and lifetime. PoL converters are commonly found in many electronic systems, usually as part of the Intermediate Bus Architecture (IBA). Their important requirements are a stable output voltage at load current variation, good temperature stability, a low output ripple voltage, high efficiency, and reliability. If the electronic system is portable, a small footprint and low volume are also important considerations. These were recently well accomplished with eGaN (enhancement gallium nitride) transistor technology, whose VUFoM (vertical unipolar figure of merit) is 1.48 compared to 1.00 for silicon. This ensures a higher converter power density (watts/area). This paper reviews the most-used capacitor technologies, highlighting the reliability of these components as part of the converter’s output filter by presenting original data related to their best performance. The test was set up with EPC’s eGaN FET transistor, which was enclosed within a 9059/30 V evaluation board with a 12 V input and 1.2 V output. Different output capacitor technologies were evaluated, and reliability was calculated based on measurements of the ripple of the output voltage and thermal scanning.

Keywords

• DC–DC converter
• eGaN
• PoL
• polymer electrolytic capacitor
• reliability
• ripple