An Isolated DC-DC Converter With Full-Duplex Communication Using a Single Pair of Transformers

This article presents a 200-MHz isolated dc-dc converter for simultaneous power and full-duplex data transfer using a single pair of transformers, for the applications of low-cost galvanic isolation. The converter operates at high frequencies using a self-oscillating topology and implements a full-duplex 4-frequency-shift keying (FSK) communication through primary-side capacitance modulation and secondary-side 1X/2X rectification. We propose an adaptive bias circuit to address the sub-harmonic oscillation issue and to minimize the power MOSFET<sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small>-resistance. The primary and secondary-side chips are fabricated in 0.18-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula> m bipolar-CMOS-DMOS (BCD) process with a 12.9-mm2 PCB transformer pair. The overall circuit achieves a 37% peak efficiency with a maximum output power of 750 mW. It transfers 54-/18-Mb/s full-duplex data with a bit error rate (BER) below 10-6.