Recent advancements in packaging and lead frame technology allow very small packages with excellent thermal dissipation performance. The TPS84620 datasheet shows the junction to ambient thermal resistance under natural convection (no airflow) to indicate how well the package removes heat from inside. The TPS84620 can easily provide the full rated 6A output current at 85ºC ambient temperature. The junction to ambient thermal resistance of the package is 13°C/W.  In the example shown, approximately 20W are delivered and the junction temperature is measured at 58.9ºC.  Therefore, under the conditions shown, the temperature rise is 30º. If the ambient temperature is 85ºC, the junction temperature would be about 118ºC, which is well below the 125ºC rating. A lower package thermal resistance increases the long term reliability of the TPS84620. Thermal pads on the bottom side of the device and a metal lead frame help direct heat to the circuit board. Allowing for adequate copper on the circuit board with vias connecting the power planes to internal circuit board layers is important to achieve good thermal results.