Thermal Design
How to compare thermal resistance, operating temperature, junction temperature, ambient limits, heat sinking, airflow, and derating curves.
Back to Engineering FAQsView Engineering GuidesAmbient temperature describes the surrounding environment, while junction temperature describes the internal semiconductor or heat-generating region. A device can meet ambient limits and still exceed junction limits if power dissipation and thermal path are not managed.
Only when the package, board condition, mounting, airflow, measurement standard, and heat path are equivalent. Theta JA, theta JC, case-to-sink resistance, and thermal conductivity describe different parts of the thermal model.
A derating curve should be treated as condition-dependent source evidence. Extract headline limits carefully, preserve the curve condition, and avoid treating a single point as a universal rating.
