The gate drivers convert the logic level PWM signals to a bipolar signal that can be used to drive the gate of power semiconductors. They also isolate the power section from the control section.
To provide power to the power section (the secondary side) isolated DC/DC converters are used. They provide a continues power of 1W. This power limits the PWM switching speed. The input voltage to the converters is 5V and their output voltages are -9V and +15V. (Used to be -15).
The formular is P=Ug²/Rg*(tr+tf)*fPWM with Ug=24V, Rg=4.7Ohms.
Example. tr=50ns, tf=110ns, fPWM=8.8kHz (SKM400GB126)
-> P=24²/4.7*(50ns+110ns)*8800Hz = 0.17W.
Please note, that this formular is an approximation. In the datasheet, together with the tr/tf times a gate resistor is stated in the conditions. If this gate resistor is less then 4.7Ohm of this driver this means that tr and tf will be a bit higher as well. If in doubt, please measure tr and tf with a scope.
Gate Drive Optocouplers
To transmit the logic level signals to the secondary side, Si8261 gate drive isolaters are used. They provide a peak drive current of 4A.