Investigating the thermal behavior of an automotive electronics unit that meets high temperature requirements

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Dr. Max Gyula
Department of Automation and Applied Informatics

This document describes the basic laws of thermal management through a realword application. Not only for the printed circuit board, but the effect of being in a closed

housing next to a motor is also taken into account. Not thoroughly, but somewhat the

dynamic behaviour is also investigated.

For this purpose the operation of the application, an automotive DC motor driver,

and briefly the characteristics of DC motors are also described.

It is worthy of note, that the thermal behaviour of a system is not only important

if the power is large. Small power applications can also exceed the limits if they do not

have adequate cooling.

The application is extraordinary respecting the operating ambient temperature, it

can also reach 140 °C, meaning more than 150 °C junction temperature for the

semiconductors. On this high temperature some, usually negligible phenomena like the

reverse leakage of Schottky diodes has to be taken into account. Disregarding this topic

could possibly result in permanent damage on the device.

For the measurements made to identify the parameters of the system a method is

described how the inner temperature sensor of a microcontroller can be calibrated to

measure the die temperature during operation with acceptable accuracy.

After identifying the system, the simulation is compared with measurements to

validate the defined model.

Based on the model and mission profile the expected maximum die temperature

is calculated.


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