On-Chip PLL-Based Methods for Synchronizing Active Switches Across the Isolation Boundary in Dc-Dc Converters

摘要

Digital isolators are widely used in isolated power converters for transmitting high-frequency gating pulses. Opto-isolators generally suffer from low reliability, while emerging RF based isolators are expensive and power-hungry. In this work, two Phase-Locked-Loop (PLL) based synchronization schemes are introduced and demonstrated to operate a bidirectional Dual-Active-Bridge (DAB) dc-dc converter. The proposed Digital Isolator Sensing (DIS) scheme utilizes a miniature air-core pulse transformer for synchronization and data communication, while the Power Transformer Sensing (PTS) scheme eliminates the need for any digital isolator for synchronization by using the power transformer. The application of DIS scheme can be extended to any topology that requires active switches on both sides of the isolation boundary, whereas the PTS scheme is designed for the DAB converter. In both schemes, the reference clock is generated on the secondary-side controller, and sensed indirectly on the primary-side. A PLL with a 100 MHz delay line, precise 12-bit phase-shift control module, and high-frequency transceiver are implemented on-chip in a 0.18μm 80V BCD process, and are used to control an off-chip DAB power stage.