Wireless charging is increasingly popular in smartwatch applications due to its seamless user experience and premium product design. However, the heat generated during wireless charging can be a safety concern. This paper presents a detailed loss model of the smartwatch wireless charging system, which includes not only the WLC circuitry loss but also the metallic material losses around the system. Two system optimizations are proposed in this paper for the smartwatch application to improve the charging and thermal performance: 1) a magnet optimized solution that reduces the metallic material loss in the smartwatch; 2) a Vrect optimized solution that shifts heat from the Rx coil to the Tx side, reducing the hot spot temperature. Both theoretical analysis and experimental results using a form factor device validate the effectiveness of these optimizations.
