Early Power Estimator User Guide

ID 683272
Date 7/16/2021
Document Table of Contents

3.1.4. Thermal Analysis

The following figure shows the Thermal Analysis section in the Main worksheet, including the junction temperature (TJ), total junction-to-ambient thermal resistance (θJA), and the maximum allowed ambient temperature (TA) values. For details about the values of the thermal parameters not listed in this user guide, click the Details button.

Figure 5. Thermal Analysis Section of the EPE Spreadsheet
Table 5.  Thermal Analysis Section Information
Column Heading Description
Junction Temp, TJ (°C)

The device junction temperature estimation based on supplied thermal parameters.

The junction temperature is determined by dissipating the total thermal power through the top of the chip and through the board (if selected). For detailed calculations, click the Details button.

θJA Junction-Ambient

The junction-to-ambient thermal resistance between the device and ambient air (in °C/W).

Represents the increase in temperature between ambient and junction for every W of additional power dissipation.

Maximum Allowed TA (°C) A guideline for the maximum ambient temperature (in °C) that you can subject the device to without violating the maximum junction temperature, based on the supplied cooling solution and device temperature grade.

You can directly enter or automatically compute the junction temperature based on the information provided. To enter the junction temperature, select User Entered T in the Input Parameters section. To automatically compute the junction temperature, select Auto Computed T in the Input Parameters section.

When automatically computing the junction temperature, the ambient temperature, airflow, heat sink solution, and board thermal model of the device determine the junction temperature in °C. Junction temperature is the estimated operating junction temperature based on your device and thermal conditions.

You can consider the device as a heat source and the junction temperature is the temperature of the device. While the temperature typically varies across the device, to simplify the analysis, you can assume that the temperature of the device is constant regardless of where it is measured.

Power from the device can be dissipated through different paths. Different paths become significant depending on the thermal properties of the system. The significance of power dissipation paths vary depending on whether or not a heat sink is used for the device.