AN4191 datasheet(4/20 Pages) STMICROELECTRONICS

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Brief introduction to Power MOSFET intrinsic gate resistance

AN4191

4/20

Doc ID 023815 Rev 1

Brief introduction to Power MOSFET intrinsic gate

resistance

Power MOSFETs are 3-pin voltage-controlled devices: with a suitable voltage applied

between gate and source, higher than the Power MOSFET threshold voltage, a current

flows through the device channel between drain and source.

Figure 1.

Power MOSFET symbol, typical circuit and device structure

Figure 1 represents the Power MOSFET symbol, a typical circuit used for characterization

tests and the device structure. The gate-source junction in the silicon is isolated by the oxide

layer (gate oxide) and the drain-source current Id flows only if Vgs > Vth is applied. Generally,

even though the oxide layer is present in the gate-source structure, a leakage current flows

through it. In other words, the gate-source structure can be represented for simplicity as a

highly capacitive impedance; the real part of the impedance is the intrinsic Rg of the

MOSFET.

The intrinsic gate resistance is an equivalent electrical resistance due to many device

structure contributions (oxide, P-body, gate finger distributions…). The Rg value is a critical

parameter that deeply impacts the device’s switching performance, together with the power

conversion efficiency and device thermal management. The higher the Rg, the larger the

device’s switching and gate drive losses, and consequently, the higher the working

temperature of the MOSFET. In this case, there is the need for additional cooling

components (i.e. heatsinks). Figure 2 shows a simple representation of the internal

parameters of a device.

AM16408v1

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