If I use XPE or XPA to estimate the power, the total on-chip power is not equal to the sum of all power supplies. Why?
This is due to one or all of the scenarios below:
- The supply power includes both on-chip and off-chip dissipated power and the user did not account for the off-chip power.
- When the process is set to "Maximum" and the minimum startup current exceeds the calculated operating current, then the startup current will be shown in the supply current summary. This means the power calculated from the "Power Supply" numbers is for startup only and the total on-chip power is for normal operation.
- According to "1", supply power should be more than on-chip dissipated power.
However, some designs in ISE Design Suite 12.3 are inconsistent with this. The work-around to solve this problem is to use 13.2 or a higher version of tools.