GaN and its challenges
GaN power transistors (labelled “GaN” in figure) are the latest and fastest power devices to emerge on the market. GaN devices won the Google Littlebox Challenge, because their sub-10ns switching speed permits converters to be made smaller with higher efficiencies than silicon or SiC power transistors. This high speed, however, causes voltage and current overshoots, which lower the power rating of converters, and oscillations which are a source of EMI.
Active gate driver for GaN
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We have developed an integrated, 10 GHz active gate driver for GaN FETs. It is the first chip to output an arbitrary waveform during the short time in which a GaN FET switches. The chip does this by actively changing the gate current every 100 ps during switching. By carefully selecting this gate current profile, voltage and current overshoots and oscillations in the GaN FETs can be reduced or even eliminated.
The driver has a powerful output stage that can deliver pulses exceeding 10 A, and has an output resistance range from 64 Ω down to less than 0.1 Ω. It can drive 400 V bridge-legs.
References
H. C. P. Dymond, J. Wang, D. Liu, J. Dalton, N. McNeill, D. Pamunuwa, S. J. Hollis, B. H. Stark, “A 6.7-GHz Active Gate Driver for GaN FETs to Combat Overshoot, Ringing, and EMI”, IEEE Transactions on Power Electronics, Vol. 33, Issue 1, pp.581-594, 2018.
D. Liu, S. J. Hollis, H. C. P. Dymond, N. McNeill and B. H. Stark, "Design of 370-ps Delay Floating-Voltage Level Shifters With 30-V/ns Power Supply Slew Tolerance," in IEEE Transactions on Circuits and Systems II: Express Briefs, vol. 63, no. 7, pp. 688-692, July 2016.