PCB Design Guidelines (HSSI, EMIF, MIPI, True Differential, PDN) User Guide: Agilex™ 5 FPGAs and SoCs

ID 821801
Date 8/29/2025
Public
Document Table of Contents

6.5.5. Power Delivery Recommendation for DDR4 Discrete Configurations

This section describes PDN design guidelines for the memory side in a memory down topology.

The total number of decoupling capacitors is based on single channel. If multiple channels are sharing the same power rail, you must scale the number of decoupling capacitors at memories for all channels accordingly. Use smaller decoupling capacitors in memory PDN design to minimize area, inductance, and resistance on the PDN path.

Table 16.  PDN Design Guidelines for the Memory Side in Discrete TopologyThis table shows the required quantity and capacitance of decoupling capacitors on the memory side.
Memory Configuration Power Domain Decoupling Location Quantity × Value (size)
Device-down 1Rx8 VDDQ/VDD shorted Four near each x8 DRAM device 36 × 1 µF (0402)
Distribute around DRAM devices 9 × 10 µF (0603)
VPP Two near each x8 DRAM device 18 × 1 µF (0402)
Distribute around DRAM devices 5 × 10 µF (0603)
VTT Place near RTT (termination resistors) 16 × 1 µF (0402)
Place near RTT 4 × 10 µF (0603)
Device-down 1Rx16 VDDQ/VDD shorted Four near each x16 DRAM device 18 × 1 µF (0402)
Distribute around DRAM devices 5 × 10 µF (0603)
VPP Two near each x16 DRAM device 10 × 1 µF (0402)
Distribute around DRAM devices 3 × 10 µF (0603)
VTT Place near RTT 8 × 1 µF (0402)
Place near RTT 2 × 10 µF (0603)