Free-air vs. Ambient Temperature

Years ago when components were more primitive, all electronic equipment had blower fans to keep the internal components cool. These fans tended to be standard and to put out a certain PSI of airflow. The temperature under these fans was called operating free-air temperature. In those days, almost all TI parts were characterized using airflow equivalent to the blower-motor output. Operating ambient temperature is measured in still air. With the advent of more modern components, the blower motor was in most cases no longer needed. IEEE and JEDEC finally made operating free-air temperature and ambient temperature synonymous. Because TI had always used the term operating free-air temperature, it was by tradition the one used on data sheets.