It is a good practice to specify the power and supply current budget for your design before generating the power report. The design power budget is the power budget for the entire device while the current budget is specified per power supply or power rail. To specify supply current budget, use the commands mentioned in Power Rail Creation and Management section. To specify power budget, use the commands mentioned in the following recommendation:
- Minimum recommended constraints
- These
constraints will ensure the power estimation checks, the power budget,
and uses the worst-case maximum process for static power
analysis.
set_operating_conditions -design_power_budget <Power in Watts>set_operating_conditions -process maximum - Additional recommended constraints
- These constraints will define the thermal solution and based on this,
Report Power will estimate the Junction Temperature and therefore the
static power more
accurately.
set_operating_conditions -ambient_temp <max Ambient requested for application is Celsius>set_operating_conditions -thetaja <the rise in junction temperature for every watt dissipated, obtained from thermal simulation, C/W>
While running Report Power, the design power and the individual power supply current are compared with this power and supply current budgets. The power report includes the power budget margin. It displays the positive margin if the design power is less than the power budget or a red negative margin, if design power exceeds power budget. If you have not provided a power budget, the report displays N/A for the margin. The following figure shows the power report when you do not specify any design power budget:
The following figure shows the power report when the design power budget is specified as 4 Watts and power margin is positive. It also displays the power margin in a negative state when the design power budget is specified as 2 Watts.
The supply current budget for each power supply is displayed in the Power Supply section. For each supply, Report Power displays positive margin when the supply current is less than the specified budget and a negative margin appears in red when supply current exceeds the specified current budget. If the current budget is not specified for any supply, then Report Power displays the current budget as unspecified and margin as N/A for that supply rail as shown in the following figure:
