Power Estimation

Kria K26 SOM Thermal Design Guide (UG1090)

Document ID
Release Date
1.0 English
The K26 SOM power estimation is done using two tools. The Power Design Manager (PDM) tool provides early power estimation. After implementation, the output from the Vivado Power Report (as described in Vivado Design Suite User Guide: Power Analysis and Optimization (UG907)) ensures the implemented design is within the SOM and carrier card constraints. Vivado Power Report only provides the power estimation for the Zynq UltraScale+ MPSoC, you must estimate the power consumption of the other peripherals on the SOM using the values found in the Thermal Loading table.
Power Tip: When designing a SOM carrier card, the PDM lists the required 5V and VCCO current requirements, which is critical for a thorough estimation. The same estimation also generates the thermal loading information needed for thermal simulation. Either your Vitis or Vivado design should be appropriately constrained for power based on the results of the estimation and thermal analysis.

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.

Figure 1. Recommended Thermal Validation Flow

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.

Figure 2. Example Showing Thermal Loading

In this example:

  1. Tj is forced to the maximum allowed for the K26C SOM (85°C)
  2. Maximum process is selected to get the worst-case static power
  3. The thermal power of the SOM components
  4. 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.

Thermal Tip: The SOM thermal model supports both the Siemens Flotherm and Ansys Icepack EDA tools. For thermal modeling assistance, the following Thermal Partners are available.

Once a capable thermal solution is designed and validated in thermal simulation, the power estimation can be refined using the simulation results.

  1. 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.
Thermal Tip: ϴJA is a measure of how the junction temperature (Tj) will increase above the ambient temperature (TA) for every watt of power dissipated (Pd) in the device, the units are °C/W. ϴJA is calculated using the following equation: ϴJA = (Tj – TA)/ PD.

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.

Use the results of your initial estimation and thermal simulations to constrain a Vitis or Vivado design to keep the power of the deployed application within the required power limits. As a minimum, use the following constraints to report power for a correct analysis of the SOM power and to accurately assess static and dynamic power:
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>
Power Tip: To get the complete SOM power estimation from a currently implemented design, load the XPE file from the report power into the PDM to estimate the power required for the other components on the SOM.
Note: For further power estimation design resources, consult the Power Design Manager User Guide (UG1556).