18.5 ZVS Flyback-Converter ICs Optimizing USB Power Delivery for Fast-Charging Mobile Devices to Achieve 93.5% Efficiency

• Main Authors: Chang, Wei-Hsu, Lin, Kun-Yu, Lee, Chun-Ching, Lo, Li-Di, Lin, Jenn-Yu, Yang, Ta-Yung
• Format: Conference Proceeding
• Language: English
• Subjects: Buck converters; Integrated circuits; Pins; Pulse transformers; Transceivers; Universal Serial Bus; Zero voltage switching
• ISSN: 2376-8606
• DOI: 10.1109/ISSCC19947.2020.9062996

USB power delivery (PD) supporting up to 100W (20V/5A) is becoming a popular standard as a charging solution for mobile devices [1]. Moreover, the extended specification includes programmable power supply (PPS) which is suitable for fast charging mobile devices by allowing the power source to dynamically adjust the constant voltage (CV) and constant current (CC) output from 3 to 21V with 20mV and 1 to 5A with 50mA resolution, respectively. To meet such a wide range and fine resolution output voltage and current regulation, the flyback converter with the secondary-side-regulation (SSR) control scheme providing the direct output voltage and current feedback is adopted [2]. Conventionally, an opto-coupler is used to feedback the compensation signal from the secondary side (SS) to the primary side (PS) of the power transformer. To avoid drawbacks of the opto-coupler, such as current transfer ratio (CTR) variation with temperature/aging and the lower frequency bandwidth, the magnetic feedback with a small pulse transformer is utilized to replace the opto-coupler. To improve the power conversion efficiency higher than the quasi-resonance (QR) flyback approach [3] while not increasing the number of components and the cost, for example by using GaN devices or active clamp circuit [4]-[6], a technique to achieve zero-voltage switching (ZVS) at the PS switch by auxiliary turn-on of the synchronous rectifier (SR) at the SS is used [7]. The commercially available USB PD flyback converter solutions use an external USB PD controller IC and external shunt-regulator-based loop compensation. To reduce the number of external components and make the power adaptor more compact, the proposed IC further integrates the USB PD controller and the CV/CC loop compensator with the internal programmableproportional-integral compensator (IPPIC).