Power Distribution System - 2020.2 English

Versal ACAP Board System Design Methodology Guide (UG1506)

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2020.2 English

Board designers are faced with a unique task when designing a power distribution system (PDS) for a Xilinx® device. Most other large, dense integrated circuits (such as large microprocessors) come with very specific bypass capacitor requirements. Because these devices are designed only to implement specific tasks in their hardened silicon architecture, their power supply demands are fixed and fluctuate typically within a certain range.

Xilinx devices do not share this property. Devices can implement an almost infinite number of applications at user-determined frequencies, and in multiple clock domains.

For this reason, it is critical that you understand the power requirements of the design, which you can assess by completing a power estimation using the Xilinx Power Estimator (XPE). Also refer to the PCB Design Guide for your device to fully understand the PDS placement and generic decoupling requirements prior to a power estimation.

Note: In XPE for Versal™ ACAP, you can select the preferred power supply consolidation and generate user-specific decoupling requirements based on the power estimation.

Key factors to consider during PDS design include:

  • Selecting the right voltage regulators to meet the noise and current requirements based on power estimation. For more information, see this link in the Versal ACAP System Integration and Validation Methodology Guide (UG1388).
    Note: To enable and simplify your power design, Xilinx partners with key power vendors to design, build, document, and test reference designs that meet all power requirements. For information, see the Power Delivery Solutions tab on the Power page of the Xilinx website.
  • Consolidating power. In the Xilinx Power Estimator (XPE), you can select between Full Power Management or Minimum Power Rails using the Solution selection on the Power Design sheet.
    Power Tip: Xilinx recommends adding a shunt resistor to allow the power on each rail to be monitored. Alternatively, you can use a PMBus-enabled regulator or current monitoring integrated circuit (IC).
  • Setting up the XADC power supply (Vrefp and Vrefn pins).
  • Running power distribution network (PDN) simulation.

    Use the recommended number of decoupling capacitors shown in the XPE Power Design sheet. These numbers are based on initial assumptions for step load per rail. However, you can edit the numbers to reflect your individual design to get more accurate requirements. Running PDN simulations can help to confirm the exact amount of decoupling capacitors required to guarantee power supplies that are within the recommended operating range.

    Note: Be sure to follow the capacitor placement shown in the Versal ACAP PCB Design User Guide (UG863).
Power Tip: Xilinx provides S-parameter models for every device, which you can access from the Power Design sheet in XPE.

For more information on PDN simulation, see Simulating FPGA Power Integrity Using S-Parameter Models (WP411).

Power Tip: Xilinx recommends simulating your power supply design using the SIMPLIS simulator in SIMetrix/SIMPLIS to ensure your design is within the Xilinx recommended operating conditions. The majority of power vendors provide a limited version of SIMPLIS and supply the models to allow you to run this simulation. SIMPLIS is a third-party software used for transient and AC analysis of voltage regulators.