TABLE OF CONTENTS This example is presented courtesy of the University of Maryland, CALCE from a 1999 paper: "Stress Balancing: A Method for Use of Electronic Parts Outside the Manufacturer Specified Temperature Range."
The Fairchild MM74HC244 is used here as an example to illustrate the stress balancing process for a hypothetical system. The maximum application ambient temperature is 85 C and the minimum application ambient temperature is ?40 C. The MM74HC244 is an octal 3-state buffer, which is typically used to buffer a bus before connecting to input or output devices. It is a CMOS logic device rated for ?40 oC to 85 C ambient temperature, and is available in a plastic dual-in-line package. The data sheet recommends operation at a supply voltage ( V CC) of 2, 4.5 or 6V. Absolute maximum rating for power dissipation at 65 C is 600mW, with a derating factor of ?12mW/ C above 65 C. This means that the maximum power dissipation of the device at 85 C (maximum operating temperature limit) is 360mW. For this example, assume that the digital logic levels of the system are 4.4 V (minimum) for high and 0.1V (maximum) for low. From the data sheet, this requires V CC=6V.
The system ambient temperature range is ?40 to +85 C, however it is assumed that a 15 C temperature rise occurs from ambient outside the equipment to ambient temperature near the device, due to internal heating effects while the equipment is operating. This results...
