ID 683174
Date 6/22/2022
Public

## 2.1.3. Environmental Conditions

The main environmental parameters affecting junction temperature are operating temperature and the cooling solution. Operating temperature primarily affects device static power consumption. Higher junction temperatures result in higher static power consumption. The device thermal power and cooling solution that you use must keep the device junction temperature within the maximum operating range for the device.

The following table lists the environmental conditions that influence power consumption.

Table 7.  Environmental Conditions that Affect Power Consumption
Environmental Condition Description
Airflow Measures how quickly the device replaces heated air from the vicinity of the device with air at ambient temperature.

You can either specify airflow as “still air” when you are not using a fan, or as the linear feet per minute rating of the fan in the system. Higher airflow decreases thermal resistance.

Heat Sink and Thermal Compound A heat sink allows more efficient heat transfer from the device to the surrounding area because of its large surface area exposed to the air. The thermal compound that interfaces the heat sink to the device also influences the rate of heat dissipation. The case-to-ambient thermal resistance (θCA) parameter describes the cooling capacity of the heat sink and thermal compound employed at a given airflow. Larger heat sinks and more effective thermal compounds reduce θCA.
Junction Temperature The junction temperature of a device is equal to:
TJunction=TAmbient+PThermal·θJA
in which θJA is the total thermal resistance from the device transistors to the environment, in degrees Celsius per watt. The value θJA is equal to the sum of the junction-to-case (package) thermal resistance (θJC), and the case-to-ambient thermal resistance (θCA) of the cooling solution.
Board Thermal Model The junction-to-board thermal resistance (θJB) is the thermal resistance of the path through the board, in degrees Celsius per watt. To compute junction temperature, you can use this board thermal model along with the board temperature, the top-of-chip θJA and ambient temperatures.