Rthja
RthJA, or thermal resistance junction-to-ambient, is a parameter used in electronics to describe how much the junction temperature of a semiconductor device rises for each watt of power dissipated when the device is in ambient conditions. It represents the overall heat path from the semiconductor die through the package and into the surrounding air, including any mounting surfaces, printed circuit board copper, heatsinks, and air movement.
RthJA is typically specified in device datasheets for a given package and mounting condition, usually under
RthJA is related to other thermal resistances. It can be viewed as the sum of junction-to-case resistance
Design use: to estimate the junction temperature Tj from ambient temperature Ta and device power P, Tj