Thermal Resistance Explained: thetaJA, thetaJC, psiJT, Power Dissipation, and Derating
Thermal resistance metrics such as thetaJA, thetaJC, and psiJT help estimate semiconductor junction temperature, but each metric has a different purpose. thetaJA is useful for standardized package comparison, thetaJC applies to controlled case or heat-sink paths, and psiJT is often used with measured package-top temperature. Buyers should review thermal data before approving power ICs, regulators, MOSFETs, and package substitutions because identical electrical ratings do not guarantee the same thermal margin.
