Based on the end-application design and operational profile, the IDD12, IDD18, and IDDIO currents could vary. Systems that exceed the recommended maximum power dissipation in the end product may require additional thermal enhancements. Ambient temperature (TA) varies with the end application and product design. The critical factor that affects reliability and functionality is TJ, the junction temperature, not the ambient temperature. Hence, care should be taken to keep TJ within the specified limits. Tcase should be measured to estimate the operating junction temperature TJ. Tcase is normally measured at the center of the package top-side surface. For more details about thermal metrics and definitions, see Semiconductor and IC Package Thermal Metrics.