Paralleling MOSFETs
Using more than one MOSFET side by side in the same switch position in order to increase current capability. The total channel resistance falls in proportion to the parallel connection: two matched MOSFETs halve the resistance and four bring it down to a quarter. Symmetrical layout and separate gate resistors are essential.
The aim of paralleling is both to carry current and to spread the heat. When two 10 mΩ MOSFETs are connected in parallel the equivalent resistance becomes 5 mΩ; at 30 A a single MOSFET produces 9 W while the pair produces 4.5 W in total and this heat is spread over two packages.
However, paralleling does not automatically bring equal sharing. During conduction the sharing is determined by the channel resistances and this behaviour is self-balancing; since the resistance rises with temperature, the device drawing excess current heats up and hands part of the current over to its neighbour.
The real risk is at the switching instant. If the gate signals arrive at different times, the MOSFET that turns on first carries the whole current alone for a while. That is why each MOSFET is given its own gate resistor, the gate tracks are routed with equal length and the source connections are joined at a common point. On the user side this means the following: a paralleled power stage provides higher current than a single-device one, and the quality of the layout determines whether that capability can really be used.
The context in which this term is used: DC motor and driver fault diagnosis matrix