By adding another lead to the source to take the majoirty of the current, the Kelvin package avoids gate ringing and false triggering which would otherwise require slowing of switching speeds to manage the large common source inductance of 3-leaded packages. The 4-leaded Kelvin connection packages offer maximum operating temperatures of 175°C with half the typical switching losses.
"We are seeing lots of new applications emerging fro 650V and 1200V and the big one we see is onboard chargers and that demands power density. One of the features we bring is being gate drive compatible with IGBTs and silicon MOSFEts which really helps people working on these problems right now," said Anup Bhalla, VP Engineering at UnitedSiC. "Then we run into the problem that the older packages such as the 3 lead are very inductive and you have problems with ringing etc and to deal with these we take fast devices and slow them down."
"Using the kelvin lead for the gate loop avoids false triggering. You have to work on layout and EMI but at least this way you can actually acheive the higher speeds," he said. "It provides an additional connection to the top of source metal – the 40 or 50A flowing has to flow through the source wires. If all of that is part of the gate driving loop there’s huge spikes. What we do with the additional lead is bypass this and make a direct connection to the source metal so all the high current is flowing the central lead so that the Kelvin lead only carries a small amount of the gate current so all the big voltage drops are not seen by the gate drive circuit."
The parts are aimed at designers of Totem Pole PFC stages, LLC and Phase Shifted Full Bridge converters, used in EV chargers, telecom and server power applications for speeds up to 500kHz.