The TPS629xx-Q1 has an extended junction temperature of 165°C versus the 125°C of the TPS621x0A-Q1. This allows the device to operate at a higher output current while still maintaining a junction temperature within the recommended range. The main two factors that play a role in determining junction temperature are efficiency and thermal resistance. Using the TPS6290x-Q1 as an example, the efficiency under a 1 MHz switching frequency, 12-V input, 1.2-V output, and 3-A load current is 83%. After subtracting the inductor power loss, the IC power loss is 468 mW, and multiplying by the junction-to-ambient thermal resistance (R_ΘJA) gives a temperature rise of approximately 34°C. With this amount of temperature rise, the ambient temperature can be as high as 130°C while staying within the 165°C recommended operating junction temperature.

In comparison, the TPS621x0A-Q1 has a lower efficiency and lower operating junction temperature. For this device the ambient temperature must stay below 100°C for the junction temperature to remain under the 125°C recommended operating junction temperature.