What is the difference between SiC FETs with kelvin source (4-Lead device), and SiC FETs without kelvin source (3-Lead device)? What are the benefits of kelvin source (KS)?
For 4L device, driver GND is connected to the KS, and power GND is connected to S; but for 3L device, both driver GND and power GND are connected to S. Compared to 3L device, 4L device separates driver signal and power loop by KS. Between KS and S pin is the package internal common source inductance. This inductance will generate voltage that counteracts the gate drive signal and cause VGS spike when device is switching (high di/dt occurs). This voltage ringing will be reflected in the gate drive loop if only power source S pin is used as for the 3L device. For the 4L device the gate drive loop is returned through KS pin and KS pin is isolated from the S pin so that the common source inductance voltage will not be reflected into gate loop and therefore achieve much cleaner gate-source waveforms and faster switching speed.
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