MOSFET Rds(on) vs Temperature

Formula

Description

MOSFET on-resistance increases significantly with temperature due to decreased carrier mobility in the silicon channel. This positive temperature coefficient is actually beneficial for current sharing when MOSFETs are paralleled, as the hotter device automatically takes less current. However, it means that the room-temperature Rds(on) from the datasheet summary significantly underestimates the actual resistance at operating junction temperatures. A typical silicon MOSFET's Rds(on) approximately doubles from 25°C to 125°C.

Variables

• RDS — Rds(on) at operating temperature (Ω)
• RDS_ref — Rds(on) at reference temperature, usually 25°C (Ω)
• tc — Temperature coefficient (typically 0.004 to 0.008 per °C for Si)
• ΔT — Temperature rise from reference (°C)

Practical Notes

Use the Rds(on) vs temperature graph from the datasheet for accurate values. GaN FETs have a lower temperature coefficient than silicon. SiC MOSFETs have nearly flat Rds(on) vs temperature. Always calculate conduction losses using the hot Rds(on), not the 25°C value. The linearized tc model is an approximation; the actual relationship is slightly nonlinear.