AN4671 datasheet(11/17 Pages) STMICROELECTRONICS

11 / 17 page

AN4671

How to minimize switching losses

DocID027654 Rev 1

11/17

2.5

Gate drive current requirements

The gate current needed to turn a MOSFET on or off can be easily calculated using the

gate charge, which can be directly read from the relevant datasheet.

The SCT30N120 total gate charge (Qg) is typically 106 nC at VDD = 800 V, ID = 20 A,

VGS = -2 to 20 V.

The image below shows the total amount of charge measured as the integral of the gate

current during turn-on.

Figure 10: SCT30N120 gate charge (turn-on at VDD=800 V, ID=20 A, Tj=25 °C)

The relatively small total gate charge that the driver must source and sink for any switching

cycle is due to the SiC MOSFET having the lowest Figure-of-Merit Rds(on)*Qg of all 1200 V

switches.

Inadequate driver current capability during sourcing and sinking will compromise the

excellent switching performance of the SiC MOSFET because, as mentioned above, the

switching energy strongly decreases with gate resistance.

For maximum switching speed, the driver must be able to source or sink the gate peak

current measured at Rg = 1

Ω, V

GS-on = +20 V and VGS-off = -2 V (see Figure 2).

The following turn-on and turn-off commutation images clearly show the driver sourcing

and sinking requirements when driving the SCT30N120.

AN4671 Datasheet(PDF) 11 Page - STMicroelectronics