Issue link: https://resources.mouser.com/i/1505196
16 \ VISHAY Industry 4.0 and Beyond T oday, a hot topic in power electronics is the design-in of gallium nitride (GaN) and silicon carbide (SiC) MOSFETs to increase efficiency and reliability by reducing power losses and operating temperatures. These new wideband materials provide hardware engineers with the opportunity to design smaller power supplies and inverters for all kinds of market segments, from industrial and medical to telecom and automotive. For predictable operation, these switches require the right driver and, of course, the right gate resistor. Driving a gate requires operating over low voltages from -8V to +18V. To charge a gate with 1nC to 1300nC—with rise times of several 10ns range cause peak current loads of mA up double-digit A range at frequencies from 10kHz to 1MHz. Due to this variation in parameters, a wide range of styles, resistive materials, and components sizes need to be considered. The common base of all gate resistors is a resistance value range between 1W and 100W. Electronic switches show variances in turn-on and turn-off times. To avoid the failure of high- and low-side switches, a separate gate resistor helps to compensate for these differences in switching behaviors. Separate gate resistors can be placed as surface-mount or through- hole devices on the driver PCB, or integrated directly inside the power module close to the gate. As a general rule, we recommend selecting an on-gate resistor value that's twice the time of the off-gate resistor. The off-gate resistance value is important in avoiding parasitic turn-on when the voltage at the drain—or in the case of IGBTs, the collector—rises up. The voltage change drives a current through the parasitic capacitance and off-gate resistor. When the voltage drop of the off-gate resistor and driver is higher than the threshold voltage of the switch, the low-side switch will turn on and cause a short. Due to high peak current and frequencies, the resistor's film temperature needs to be kept as low as possible, as higher temperatures can cause resistance values to drift higher over time. And unfortunately, what seems to work in the lab might end in disaster after only a hundred hours of operation in the field. To avoid these catastrophic failures, stable resistor materials like thin film or metal film (e.g., NiCr or TaN) should be considered. Electronic Switches: Driving a Gate Requires the Right Resistor