28 AC/DC DC/DC https://www.analog.com/ Issue 3 2025 Power Electronics Europe www.power-mag.com FETs have slow turn-on/off characteristics (in the tens of ns). Therefore, the dead time is set longer to prevent shoot through. The LT8390A has a set 25ns dead time, which is a shorter dead time compared to many synchronous controllers on the market. While this is suitable for high frequency, high power MOSFET control, it is still too long for GaNFETs. GaNFETs can turn on extremely quickly (in the ones of ns). Therefore, to mitigate additional conduction losses during the dead time, it is recommended to add a catch Schottky diode in antiparallel with the synchronous GaNFET to divert the conduction to a less lossy pathway. D1 and D2 in Figure 2 show which FET to place the Schottky diodes across. D1 is placed across the synchronous buck side FET, and D2 is across the synchronous boost side FET. For a simple buck converter, only D1 is required. For a simple boost, use D2. Higher Power with Higher Frequency The LT8390A has a switching frequency up to 2MHz. GaNFETs have significantly lower switching losses compared to Si MOSFETs, enabling similar power losses at higher switching frequencies and voltages. The EVAL-LT8390A-AZ GaNFET board demonstrates the efficiency and compact size advantages of using GaNFETs by setting the switching frequency to 2MHz. With an output of 24V, the GaNFETs can produce 120W of power at room temperature. The board size is comparable to the previous LT8390A evaluation board: the DC2598A, which uses silicon MOSFETs and provides a 12VOUT with 48W power. Figure 3 shows the maximum power capability of a 2MHz GaN buck-boost, while Figure 4 compares the efficiency of both boards. Even at higher voltages, and 2.5? output power, the GaNFET board produces better efficiency than the Si MOSFET board. The utilisation of GaNFETs allows operation at higher voltages and power with a similar board area. Conclusion If there are no DC-to-DC controllers that specifically have GaNFET driving capabilities, it is still possible to drive them effectively. Even using a controller originally meant to drive Si MOSFETs, the EVALLT8390A-AZ can easily outpower and achieve higher efficiency in a similar board area. Table 1 shows a wide selection of recommended controllers for driving GaNFETs. For even higher power requirements, such as paralleled buckboost GaNFET control, please contact the factory. By researching a controller that offers a 5V gate driver and incorporating additional external protection circuit components, it is possible to drive GaNFETs safely and explore more options in power conversion design. Analog Devices: www.analog.com About the Author Kevin Thai is an applications manager with Analog Devices in San Jose, California. He works in the IPS Power Products Group and oversees the isolated flyback and protection product lines along with other boost, buck-boost, and GaN controller products. He received his B.S. degree in electrical engineering from Cal Poly, San Luis Obispo, in 2017, and M.S. degree in electrical engineering from University of California, Los Angeles, in 2018. !"#$%&'(&)*+,-+)*&*-.,/-$$%/0&*-12",3#$%&43,5&6"789!0& $ b*%"BB*')*)$ 9&:$ 6"'08">>*8+$ $ ="?">"-A$ I&E$ ('?30`$ J30?30$ Z">0&-*$ $ G#,0%1,'-$ ;8*D3*'%A$ ! "#$!%#&'!&'#()*'+! $ $ $ $ P=6SQTU$ $ $ $ 53&>$ 23%4$9&:$ %"'08">>*8$ $ $ $ $ RUUZ$ $ $ $ $ RUU4!N$0"$WI!N$ ►$ GB&80$2""0+08&?$ ►$ G?>,0$-&0*$)8,7*$ ►$ GB&80$'*&8/N*8"$ )*&)$0,B*$ ►$ O)c3+0&2>*$S'+$0"$$ [U'+$)*&)$0,B*$ $ $ $ $ P=6SQTR$ $ $ $ \3%4$9&:$ %"'08">>*8$ $ $ $ $ RUUZ$ $ $ $ $ RUU4!N$0"$WI!N$ ►$ GB&80$2""0+08&?$ ►$ G?>,0$-&0*$)8,7*$ ►$ GB&80$'*&8/N*8"$ )*&)$0,B*$ ►$ O)c3+0&2>*$ S'+$0"$[U'+$ $ )*&)$0,B*$ $ $ $ $ P=Q.RQ$ $ $ $ $ !&>@/28,)-*$ 9&:$-&0*$ )8,7*8$ $ $ $ $ RUUZ$ $ $ $ $ d?$0"$RUI!N$ ►$ P"#$?8"?&-&0,"'$ )*>&A$ ►$ ;&+0$&')$?"#*8@3>$$ -&0*$)8,7*$ ►$ G?>,0$-&0*$)8,7*$ ►$ GB&80$2""0+08&?$ ►$ 9&0*$)8,7*$"7*8/$ 7">0&-*$>"%4"30$ $ P=QWTU`$ P=QWTUO`$ P=QWTX$ $ ./+#,0%1$ 23%4/2""+0$ %"'08">>*8$ $ $ [UZ$ P=QWTU`P=QWTX]$ RYU4!N$0"$ [YU4!N$ P=QWTUO]$[UU4!N$ 0"$XI!N$ ►$ G,$IJG;<=$ %"'08">>*8$#,01$ YZ$-&0*$)8,7*8$ $ P=QWTR`$ P=QWTRO`$ P=QWTR5$ $ ./+#,0%1$ 23%4/2""+0$ P<5$)8,7*8$ %"'08">>*8$ [UZ$ P=QWTR`P=QWTR5]$ RYU4!N$0"$ [YU4!N$ P=QWTRO]$[UU4!N$ 0"$XI!N$ ►$ G,$IJG;<=$ %"'08">>*8$#,01$ YZ$-&0*$)8,7*8$ To receive your own copy of Power Electronics Europe subscribe today at: www.power-mag.com
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