An accurate power estimation is critical to defining an effective thermal solution and keeping the K26 SOM components below their maximum junction temperature (Tj). When designing the K26 SOM thermal solution, the worst-case power is the starting point for simulation. Once a thermal solution is defined and the Tj is within the limits, the theta JA (ϴJA) of the system can be input back into the PDM for a more accurate estimation of the power requirements for the K26 SOM.
Based on the temperature grade of the commercial temperature grade K26C SOM or the industrial temperature grade K26I SOM, the junction temperature should be forced to the maximum desired operating temperature (often maximum device operating temperature) to get the worst-case power estimation for the K26 SOM. The following example shows the K26C SOM when the Tj is forced to 85°C. The power dissipation of each of the components on the SOM is shown in the Thermal Loading table.
In this example:
- Tj is forced to the maximum allowed for the K26C SOM (85°C)
- Maximum process is selected to get the worst-case static power
- The thermal power of the SOM components
- Total electrical power required on the SOM 5V connector is based on the current estimation
The thermal loading in the PDM matches the components in the SOM thermal model, the thermal power for every component listed should be added. The PCB also has a small amount of power loss to account for an inductor or other ancillary components, this power should be applied to the PCB in the model.
Once a capable thermal solution is designed and validated in thermal simulation, the power estimation can be refined using the simulation results.
- Apply the calculated effective ϴJA of the system in the PDM along with the maximum supported Ta for the product. This is the recommended approach because the power estimation dynamically estimates the anticipated Tj and provides a more accurate estimated power.
The following example shows a TA of 25°C with a ϴJA of 3.9°C/W and the estimate Tj based on the current estimation is 52°C, which is a more accurate total power estimation for the SOM. The total power at 52°C is 8.7W, compared to 9.7W at 85°C in the worst-case estimate.
set_operating_conditions -design_power_budget <Power in Watts>
set_operating_conditions -process maximum
set_operating_conditions -ambient_temp <Max Supported by Application>
set_operating_conditions -thetaja <Increase in Tj for every W dissipated C/W>