A proper gate control is crucial for system performance. This is valid for all power switches, and it is valid for gallium
nitride (GaN)
comprises both common enhancement-mode (normally-off) concepts. They utilize a p-doped gate to shift the
threshold voltage from the inherently negative value (normally-on) to a positive value. Depending on the realization of
the gate contact, the resulting devices are either r
exclusively used in high-voltage applications (up to 700 V), SGTs cover a broader voltage range from 100 to 700 V.
Essentially, the gate drive considerations discussed in this document are valid for all voltage classes.
All GaN switches are characterized by low terminal capacitances, and this results in a gate charge that is almost an
order of magnitude lower than that of their silicon counterparts. Thus the driving capability of standard MOSFET
drivers is usually more than sufficient for driving GaN transistors. However, there is a parameter typical for
enhancement-mode (e-GaN) switches that significantly influences gate drive concepts. It is the low threshold voltage of
the p-GaN gate, typically only slightly above +1 V. This has severe consequences:
a relatively small gate current for switch-off at zero gate voltage
an increased sensitivity with respect to cross-conduction in half-bridge applications
Both these effects can be mitigated by using a negative gate drive voltage. But there are also drawbacks associated
with this measure, as a negative gate drive causes an increased voltage-drop in reverse (third quadrant) operation and
thus higher conduction losses during dead-time. The optimum gate drive thus always depends on basic application
conditions (hard/soft-switching, power class, switching voltage, frequency, etc.).
This whitepaper gives a compact overview of the recommended gate drive concepts for both GIT and SGT product
families. A versatile standard drive (RC interface) can be easily adapted to both technologies. The document also
provides basic gate drive dimensioning guidelines and some typical application examples.
This whitepaper gives a compact overview of the recommended gate drive concepts for both GIT and SGT product families, and also provides basic gate drive dimensioning guidelines and some typical application examples.