TA Operating Free Air Temperature

TA Operating Free-Air Temperature

JEDEC – no definition offered

TI – The range of operating temperatures over which the logic element is specified.

In digital-system design, consideration must be given to thermal management of components. The small size of packages makes this more critical. The Figure below shows the high-effect (high-K) thermal resistance for the 5-, 14-, 16-, and 20- pin packages for various rates of airflow calculated in accordance with JESD51-7.

The thermal resistances in the Figure can be used to approximate typical and maximum virtual junction temperatures. In general, the junction temperature for any device can be calculated using the following equation:

TJ = RqJA × PT + TA


TJ = virtual junction temperature (C)

RqJA = thermal resistance, junction to free air (C/W)

Pt = thermal resistance, junction to free air (W)

TA = free-air temperature (C)


This tutorial is based on the Understanding and Interpreting Standard Logic Data Sheets application report (SZZA036).  To download the full PDF version of this application report, please use the following URL:  http://www.ti.com/lit/szza036