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Thermal-Resistance of DC/DC Converters with Power MOSFETs

Autor / Redakteur: Peter Miller, Rich Nowakowski * / Dipl.-Ing. (FH) Thomas Kuther

Since operating temperature contributes to the performance and reliable life span of semiconductor devices, conducting thermal analysis on power devices is an important part of the design process.

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Figure 1. TPS543C20 40-A thermal image at 0.9-V output with 12-V input, at 25°C ambient
Figure 1. TPS543C20 40-A thermal image at 0.9-V output with 12-V input, at 25°C ambient
(Source: Texas Instruments)

Understanding thermal information from a DC/DC converter data sheet is a critical component of thermal analysis. The data sheets for most modern power devices provide thermal-resistance tables and thermal images (Figure 1) to help designers with their thermal analysis. However, understanding the information in the data sheet is not always direct or easy.

This article presents assumptions that analog designers may make for thermal analysis. The analysis for each assumption is followed with insights to decipher the actual thermal information in the data sheet. The device used for analysis is a high-current DC/DC converter capable of delivering 20 A to 30 A of output current at a low output voltage from a 12-V input.