Impact of Kelvin-Source Resistors on Current Sharing and Failure Detection in Multichip Power Modules

The use of a kelvin-source (sometimes referred to as an auxiliary-source) terminal is becoming common in fast switching semiconductors such as Silicon Carbide MOSFETs. The kelvin-source terminal decouples the path of the load current from the path of the control current, leading to improved switching characteristics. However, in multiple paralleled chips, kelvin-source connections sometimes lead to load current imbalances among the bondwires of each paralleled chip. A simple method to prevent this is to introduce kelvin-source resistors. This paper investigates the sizing of kelvin-source resistors and their subsequent impact on current balancing. This investigation has primarily been conducted in the context of using the kelvin-source resistor as a failure detection sensor. We find that a kelvin-source resistor of 0.5Ω to 1Ω is adequate for current balancing purposes, however for dual purpose use as a failure sensor, a value of 2Ω or more may be recommended.