Origin of Common Source Inductance in Power Device Packages with Kelvin Source Terminal

The kelvin-source packages are becoming popular for high-power ultrafast switching devices to reduce the common source inductance (CSI), which induces the noise voltage in the gating circuit at the transitional change of the drain current and causes false triggering. Despite its importance, however, the actual measurement of CSI has not been reported for kelvin-source packages due to their small inductance values. This paper measured the CSI of typical kelvin-source package TO-247-4L. The result revealed that the CSI of this kelvin-source package ranged 0.2nH–0.7nH, which cannot be neglected at a switching speed greater than 1A/ns. Furthermore, this variation in CSI was found to arise from the magnetic coupling between the bonding wires of power source and gating source, implying that separating the bonding wires can further reduce the CSI.