A high-efficiency transformer-in-package isolated DC-DC converter using glass-based fan-out wafer-level packaging

A transformer-in-package (TiP) isolated direct current–direct current (DC-DC) converter using glass-based fan-out wafer-level packaging (FOWLP) is proposed. By using 3-layer redistribution layers (RDLs), both the transformer and interconnections are built without an additional transformer chip, and the converter only has 2 dies: a transmitter (TX) chip and a receiver (RX) chip. The proposed solution results in a significant reduction in the cost and makes major improvements in the form factor and power density. Moreover, the transformer built by the RDLs achieves a high quality factor (Q) and high coupling factor (k), and the efficiency of the converter is thus improved. The TX and RX chips were implemented in a 0.18 µm Biopolar CMOS DMOS (BCD) process and embedded in a compact package with a size of 5 mm × 5 mm. With an output capacitance of 10 µF, the converter achieves a peak efficiency of 46.5% at 0.3 W output power and a maximum delivery power of 1.25 W, achieving a maximum power density of 50 mW/mm².