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5.4.3. Power Delivery Recommendation for DDR4 Discrete Configurations
This section describes PDN design guidelines for the memory side in memory down topology.
The total number of decoupling capacitors is based on single channel; if multiple channels are sharing the same power rail, the number of decoupling capacitors at memories for all channels should be scaled accordingly. You can use smaller decoupling capacitors in memory PDN design to minimize area, inductance, and resistance on the PDN path.
The following 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 | 4 near each x8 DRAM device | 36 × 1 uF (0402) |
Distribute around DRAM devices | 9 × 10 uF (0603) | ||
VPP | 2 near each x8 DRAM device | 18 × 1 uF (0402) | |
Distribute around DRAM devices | 5 × 10 uF (0603) | ||
VTT | Place near Rtt (termination resistors) | 16 × 1 uF (0402) | |
Place near Rtt (termination resistors) | 4 × 10 uF (0603) | ||
Device-down 1Rx16 | VDDQ/VDD shorted | 4 near each x16 DRAM device | 18 × 1 uF (0402) |
Distribute around DRAM devices | 5 × 10 uF (0603) | ||
VPP | 2 near each x16 DRAM device | 10 × 1 uF (0402) | |
Distribute around DRAM devices | 3 × 10 uF (0603) | ||
VTT | Place near Rtt (termination resistors) | 8 × 1 uF (0402) | |
Place near Rtt (termination resistors) | 2 × 10 uF (0603) |