Environment Tab - 2020.2 English

Review the different user-editable selections in the Environment tab. Make sure the process, voltage and environment data closely match your expected environment. These settings have a significant influence on the total estimated power. The user-editable selections in the Environment tab are:

Device Settings

Temp grade

Select the appropriate grade for the device (typically Commercial or Industrial). Some devices may have different device static power specifications depending on this setting. Setting this properly will also allow for the proper display of junction temperature limits for the chosen device.

Process

For the purposes of a worst-case analysis, the recommended process setting is Maximum. The default setting of Typical will give a closer picture to what would be measured statistically, but changing the setting to Maximum will modify the power specification to worst-case values.

Environment Settings

Output Load (pF)

The board and other external capacitance driven by the outputs in the I/O ports.

Junction temperature (°C)

Specify a value to force the device junction temperature to a specific value. For worst-case analysis, force this value using user override check-box to TJ (Max) based on the temperature grade of the part.

Ambient temperature (°C)

Specify the maximum possible temperature expected inside the enclosure that will house the device design. This, along with airflow and other thermal dissipation paths (for example, the heatsink), will allow an accurate calculation of Junction Temperature which in turn allows more accurate calculation of the device static power.

Effective ΘJA (°C/W)

Specify the value for custom ΘJA which is generally derived from thermal modeling. Ambient Temperature and Effective θJA are to be set if the values are derived from thermal simulations for better accuracy in estimation.

Airflow (LFM)

The airflow across the chip is measured in Linear Feet per Minute (LFM). LFM can be calculated from the fan output in CFM (Cubic Feet per Minute) divided by the cross sectional area through which the air passes. Specific placement of the device and/or fan may have an effect on the effective air movement across the device and thus the thermal dissipation. Note that the default for this parameter is 250 LFM. If you plan to operate the device without active air flow (still air operation) then the 250 LFM default has to be changed to 0 LFM.

Heat sink (if available)

If a heatsink is used and more detailed thermal dissipation information is not available, choose an appropriate profile for the type of heatsink used. This, along with other entered parameters, will be used to help calculate an effective ΘJB, resulting in a more accurate junction temperature and quiescent power calculation. Note that some types of sockets may act as heatsinks, depending on the design and construction of the socket.

Board selection and Number of board layers (if available)

Selecting an approximate size and stack of the board will help calculate the effective ΘJB by taking into account the thermal conductivity of the board itself.

ΘJB

In the event more accurate thermal modeling of the board and system is available, ΘJB (printed circuit board thermal resistance) should be used to specify the amount of heat dissipation expected from the device.