WEBENCH® Tools/TPS53355: TPS53355 junction temperature

Hi Jimmy,

The thermal information table on page 6 uses the JEDEC standard board. The application report linked below the table provides more details.

The SOA curves on page 14 in figures 32 and 33 would be measured using the EVM.

Anthony

Hi Jimmy,

The junction temperature calculation in WEBENCH is a relatively simple calculation using a Theta JA of 27.2 °C/W which is actually quite pessimistic. Lower Theta JA can be expected in a real board design. For example, in the default design the TPS53355 has a power dissipation of 1.4W and 30°C ambient temperature. 30°C + 1.4W*27.2°C/W = 68.1°C.

This number is from the JEDEC standard simulation which does not include Airflow with the JEDEC standard layout which is a 4 layer board with a relatively small amount of copper. In a real application, you can expect much better performance than this. For example, if I up the design to 30 A to match the thermal image in the TPS53355 EVM user's guide, WEBENCH estimates a junction temperature of 128.3 °C while the measurement in the user's guide shows 88.6 °C. Assuming the power dissipation in WEBENCH matches the EVM exactly, this means the EVM Theta JA is around (88.6°C-25°C)/3.8W = ~17°C/W.

More details on the JEDEC standard can be found in http://www.ti.com/lit/pdf/SPRA953