An Experimental Comparison of Galvanically Isolated DC-DC Converters: Isolation Technology and Integration Approach

Egidio Ragonese,Nunzio Spina,Alessandro Parisi,Giuseppe Palmisano

doi:10.3390/electronics10101186

Egidio Ragonese, Nunzio Spina + Show 2 more

Open Access

https://doi.org/10.3390/electronics10101186

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Journal: Electronics	Publication Date: May 15, 2021
Citations: 14	License type: CC BY 4.0

Affiliation: University of Catania, STMicroelectronics (Italy)

Abstract

This paper reviews state-of-the-art approaches for galvanically isolated DC-DC converters based on radio frequency (RF) micro-transformer coupling. Isolation technology, integration level and fabrication issues are analyzed to highlight the pros and cons of fully integrated (i.e., two chips) and multichip systems-in-package (SiP) implementations. Specifically, two different basic isolation technologies are compared, which exploit thick-oxide integrated and polyimide standalone transformers, respectively. To this aim, previously available results achieved on a fully integrated isolation technology (i.e., thick-oxide integrated transformer) are compared with the experimental performance of a DC-DC converter for 20-V gate driver applications, specifically designed and implemented by exploiting a stand-alone polyimide transformer. The comparison highlights that similar performance in terms of power efficiency can be achieved at lower output power levels (i.e., about 200 mW), while the fully integrated approach is more effective at higher power levels with a better power density. On the other hand, the stand-alone polyimide transformer approach allows higher technology flexibility for the active circuitry while being less expensive and suitable for reinforced isolation.

Highlights

Safety rules for equipment operated by human beings, along with severe reliability requirements for electronics in harsh environments, call for galvanic isolation in several application fields, even at very low power levels, as summarized in Figure 1a [1]
The most efficient solution is the D-class oscillator with cross-coupled transistors working as power switches (Figure 3a), which boosts the drain voltages above the supply voltage, V DD [12,13]. This solution requires the cross-coupled pair to be implemented with special transistors with very high breakdown for drain voltage, such as the laterally diffused transistors (LDMOS) that are usually integrated into the bipolar-CMOS-DMOS
A crucial role in the performance of a galvanically isolated DC-DC converter is played by the isolation transformer, whose characteristics affect system power efficiency and maximum isolation rating, as well as the integration level and overall costs

Summary

Introduction

Safety rules for equipment operated by human beings, along with severe reliability requirements for electronics in harsh environments, call for galvanic isolation in several application fields, even at very low power levels, as summarized in Figure 1a [1]. Power levels from a few tens of mW to about 1 W can be transferred across the galvanic barrier by means of magnetic coupling. To this aim, micro-transformer devices are currently used, which exploit a dielectric layer between two stacked spiral windings to withstand an isolation voltage of several kilovolts [2,3]. Formance isolated output power and efficiency), integration level, design fl and fabrication costs in order to highlight the pros and cons of the two approach The paper is organized as follows.

Galvanically

Galvanically Isolated DC-DC Conversion

Isolation Technology

Integrated Isolation Transformers

ExperimentalAn

Experimental Comparison

Conclusions