XPE reports that a total current on VCCINT of at least 0.4A is required during startup for the Spartan-6 XC6SLX16 -2C production device when calculated for maximum process. 0.48A is the current required on the VCCINT supply during startup for the Spartan-6 XC6SLX45 -2C production devices. If this value exceeds the value calculated from the power estimators based on utilization and dynamic operating current, a warning message is shown that "Maximum startup current exceeds total estimated ICCINT." Other densities, speed grades, and operating conditions do not have this same requirement, and can have a much lower VCCINT total current requirement, especially for low-speed, low-utilization designs.
Use the Xilinx Power Estimator tool to estimate maximum current requirements for your specific device and conditions.