Table 1. Comparing switching performance of Silicon and GaN transistors
Table 1 shows that a 100V MOSFET increases the FOM by a factor of 2.3 and the gate drive power by a factor of 2.4 compared to the 40V MOSFETs. However, the 100V GaN E-HEMT transistor, having exceptionally good switching performance, offers a FOM even lower than the 40V MOSFET. This allows DC-DC converter architects to reach the high efficiency and high frequency requirements of 48V high-density communications processing boards.
Design of GaN 48V to 12V DC-DC converter
In order to compare the actual performance of GaN technology to silicon technology, the 48V to 12V DC-DC converter shown in Figure 2, using GaN transistors, was created. For this test, the GS61008P from GaN Systems in Canada was used. The electrical characteristics of this device allows for both high frequency and high efficiency. The embedded packaging technique known as GaNPX results in very low package inductance, and a very low inductive loop overall, which reduces noise, losses and improves efficiency.
Figure 2. 48V to 12V DC-DC converter using GaN transistors. [Editor’s note; this diagram is abridged to focus on the current path from the input voltage lines: a more complete version showing the output configuration is at; gansystems.com/evaluationboards/GS61008P-EVBBK-REVC-Schematics.pdf]
Thermally, this converter uses no heat sink. The GS61008P has a very low thermal impedance of 0.55 °C/W, allowing cool operation. As recommended by GaN Systems, there are vias used underneath each of the two devices to help conduct heat to the ground plane. At an operating current of 10A, at 25°C and with 500 linear feet per minute (LFM) airflow, the top and bottom device junction temperatures are 43°C and 42°C respectively.
The GS61008P GaN E-HEMT transistor operates best with a gate voltage of 0V (OFF) to 6V (ON). One specific feature of GaN Systems’ technology, with regards to