The previous equations for thermal resistance due to conduction, convection, and heat radiation are usually summarized into two parameters in the datasheet: the Theta J-A (θJA) is the thermal resistance from the junction to the ambient environment and heat dissipation occurs over multiple thermal paths. The Psi J-T (ΨJT) is the thermal characterization parameter from the junction to the center of the top surface of the package. The ambient temperature (T_A) is the temperature of the air in the vicinity at a position where there is no effect from the component being measured, such as outside the boundary layer of the heat source. The θJA and ΨJT are data at the time of mounting on a JEDEC specified printed circuit board.