The reference design of Figure 2 was built and tested, and efficiency was measured at various operating points. Figure 4 depicts test results while operating this reference design, and also compares the efficiency at 300 kHz to a similar referenced design using a 100V Silicon MOSFET.
Figure 4. GaN delivers the highest efficiency and operates easily at 2 MHz
Figure 4 clearly shows that at 300 kHz, the efficiency of GaN is substantially higher than very highly rated 100V silicon MOSFETs. This is due to the better FOM figures, the lack of Qrr losses, and the significantly lower gate drive losses. With a 48V system using 100V devices, GaN transistors should be used for the highest efficiency.
The efficiency testing was started at 300 kHz using a 10 µH Coilcraft inductor, part number SER2918H-103. The frequency was then adjusted to 1 MHz, and a 2 µH Coilcraft inductor approximately five times smaller was used. This demonstrates that a higher density DC-DC converter can be designed that still reaches very high efficiency values. Finally, the unit was tested at 2 MHz, again resulting in a very highly efficient, stable design.
The final analysis
48V datacentres and communications systems will require DC-DC converter designers to learn how to maximize efficiency using 100V transistors. GaN E-HEMT transistors, when compared to Silicon MOSFETs at 100V and even at 40V, offer a significant improvement in FOM and gate drive performance, allowing designers to achieve high frequency, high power density designs at very high efficiency levels.
Di Chen is Applications Engineering Manager and Jason Xu is an Applications Engineer, at Canadian company GaN Systems .