Multiple power supplies are required to power a device and must be provided in a specific sequence. Consider the use of power monitoring or sequencing circuitry to provide the correct power-on sequence to the device as well as any additional active components on the board. More complex environments might benefit from the use of a microcontroller or system and power management bus such as SMBUS or PMBUS to control the power and reset process. Specific details of rail consolidation, sequencing, and other details necessary for proper power delivery design can be found in the Power Design tab of the Power Design Manager (PDM) tool (download at www.xilinx.com/power).
The separate sources provide the required power for the different device resources. This allows different resources to work at different voltage levels for increased performance or signal strength, while preserving a high immunity to noise and parasitic effects.