New 200 V eGaN Devices Double the Performance Edge Over the Aging Silicon Power MOSFET.

New 200 V eGaN Devices Double the Performance Edge Over the Aging Silicon Power MOSFET.

8 21, 2020

Efficient Power Conversion (EPC) is doubling the performance distance between the aging silicon power MOSFET and eGaN® transistors with 200 V ratings.  The new fifth-generation devices are about half the size of the prior generation.  This performance boost comes from two main design differences, as shown in figure 1.  On the left is a cross-section of the fourth generation 200 V enhancement-mode GaN-on-Si process.  The cross-section on the right is the fifth-generation structure with reduced distance between gate and source electrodes and an added thick metal layer. These improvements, plus many others not shown, have doubled the performance of the new-generation FETs.

Figure 1: A comparison between the fourth-generation GaN FET cross-section (left) and the fifth-generation device (right).  Note the closer spacing between the gate and drain in the fifth-generation product as well as the addition of a fourth metal layer.

The first two products, EPC2207 and EPC2215, are shown in figure 2 and are compared against the prior generation eGaN FETs.  For example, the EPC2207 is 2.6 mm2 compared with the EPC2010C at 5.8 mm2, yet the EPC2207 has lower RDS(on), lower QG, QGD, and much lower QOSS.

Figure 2:  The fifth-generation products compared against their fourth-generation predecessors.  The power density is approximately double.

To illustrate the significant performance advantage over Si power MOSFETs, figure 3 compares both the fourth generation and fifth generation eGaN FETs against a benchmark silicon device, the IPT111N20NFD from Infineon.  The EPC2215 has 33% lower RDS(on), yet is 15 times smaller in size.  Gate charge (QG) is more than six-time smaller with the new technology, and like all eGaN FETs, there is no reverse recovery charge (QRR) enabling lower distortion class D audio amplifiers as well as more efficient synchronous rectifiers and motor drives.

Figure 3: The fourth and fifth-generation eGaN FETs compared against a benchmark Si power MOSFET.  The fifth-generation doubles the performance gap that was already quite large at the fourth generation.

Additional confirmation of the advantages of the new-generation 200 V eGaN FETs seen in the performance graphs in figure 4.  Shown is a comparison between the Infineon 200 V MOSFET benchmark device, the older-generation EPC2034C, and the fifth-generation EPC2215.  The EPC2215 performs better than the older EPC2034C despite being 60% the size.  The Si MOSFET has a clearly inferior performance.

Figure 4: Efficiency comparison between Infineon IPT111N20NFD, the EPC2034C generation 4 eGaN FET, and EPC2215 generation 5 eGaN FET in a 150 V to 12 V DC-DC buck converter.

With devices as small as these new generation eGaN FETs, a common question is how well they can dissipate heat in operation.  Thanks to the chip-scale packaging, thermal efficiency is much higher than the comparable silicon device in a package.  As an example, in figure 5 is a 4 mm2 eGaN FET showing 4 °C/W thermal resistance with 6 W power in the device.  We show a simulated image for clarity, but the actual capability of the device was experimentally confirmed.

Figure 5: Thermal image from a simulation of a 4 mm2 eGaN FET showing a thermal resistance of 4°C/W.  This performance was experimentally verified.

With the clear superiority of these new 200 V eGaN FETs, one might expect them to be priced at a premium.  However, EPC has priced these state-of-the-art transistors comparable with their aging ancestor, the silicon power MOSFET.

The applications for these leading-edge devices include class D audio, synchronous rectification, solar MPPTs (maximum power point tracker), DC-DC converters (hard-switched and resonant), and multi-level high voltage converters.

In figure 6 is a 2.5 kW, 4-level totem pole PFC using only six EPC2215 devices.  By stacking the 200 V rated eGaN FETs, the input voltage for this PFC can go up to 400 V and, as shown in figure 7, achieve 99.25% efficiency.

Figure 6: Circuit diagram and photo of the 2.5 kW four-level totem-pole power factor correction (PFC) circuit.  This system uses six EPC2215 devices to allow an input voltage as high as 400 V.
Figure 7: Efficiency versus load power for the system in figure 6.  Peak efficiency reaches 99.25% with full-load efficiency above 99%.

EPC’s fifth-generation eGaN FETs achieve higher performance in a smaller, more thermally efficient size, and at a comparable cost.  In addition to the buck converter in figure 4, and the totem pole PFC in figure 6, these new-generation 200 V eGaN FETs are ideal for 49 VOUT synchronous rectification and class d audio applications. The inevitable obsolescence of the aging power MOSFET is becoming more evident every day.