When considering the power estimation of a design, understanding the efficiency of the thermal solution is crucial. The lower the junction temperature, the lower the static power of a design.
Xilinx recommends using lidless packaging if it is available for your device. Lidless packaging offers a more efficient thermal solution and allows direct contact with the heat source, removing a thermal interface material (TIM) layer. Xilinx lidded and lidless parts have the same handling and manufacturing requirements. The following figure compares the heat sink application for a lidded and lidless device.
- Junction Temperature Tj
- You can override this setting to a desired junction temperature to match your thermal simulation. If you are not running a thermal simulation, set the junction temperature to the worst case.
- Effective ΘJA
- Describes the thermal efficiency of a thermal solution, the units are measured in degrees Celsius per watt (°C/W). For example, an ΘJA of 2.1°C/W means that for every watt dissipated in the device, the junction temperature increases by 2.1°C. For a 10W design, the increase is 21°C above the ambient temperature.
The following figure shows the recommended flow for thermal validation.
After the junction temperature is within specification and sufficient margin is considered, the thermal solution is considered effective.
# Standard Constraints:
set_operating_conditions -process Maximum
set_operating_conditions -design_power_budget <value>
#If thermal simulation completed
set_operating_conditions -ambient_temp <value>
set_operating_conditions -thetaja <value>
#Else if no thermal simulation completed
set_operating_conditions -junction_temp <value>