Common source inductance (CSI) of power devices and the impacts on synchronous buck converters

Common Source Inductance (CSI) is the inductance shared by the main current loop and the gate drive loop in a synchronous buck converter. Any voltage induced on CSI will change the effective gate-source voltage of the FET and has significant impacts on converter performance. This paper will explore and verify the impacts of High Side (HS) CSI on converter switch node ringing and power loss. New equations will be proposed to provide more accurate power loss estimations and help converter designs. Power MOSFET example with advanced package will be given to demonstrate converter efficiency improvement brought by minimized HS CSI. The paper will also discuss Low Side (LS) FET CSI effects on converter performance.