When x1 (single) memory (DDR4) device (x1
(single), 16-bit) is used, the recommendation is to follow point-to-point topology
(connections).
Summary of point-to-point topology
implementation:
- For differential clock DDR0_CK0,
DDR0_CK0_n, AC termination x2 R in series (value = Zo − Single-ended impedance) and a
filter capacitor 0.01μF or value recommended by the memory manufacturer connected to the
center of two resistors and DDR PHY IO supply VDDS_DDR is recommended.
- VREFCA (VDDS_DDR/2) is the reference
voltage used for control, command, and address inputs to the memory (DDR4) devices. When
VTT terminations and VTT termination LDO is not used, VREFCA is derived from VDDS_DDR
using a resistor divider (two resistors (1kΩ, ±1%, recommended value) connected across
VDDS_DDR and VSS) with a filter capacitor (0.1μF, recommended value) connected in
parallel to the resistors. An additional decoupling capacitor is recommended near to the
VREFCA pin (close to memory (DDR4) device).
- External VTT terminations for address
and control signals are optional.
When VTT terminations are used for the
address and control signals when x1 DDR4 is used, use a Sink or Source DDR Termination
Regulator (LDO) to generate the required VTT supply.
When x2 (two) memory (DDR4) devices (x2
(two), 8-bit) are used, the recommendation is to follow Fly-by topology (connections).
Summary of Fly-by topology
implementation:
- External VTT terminations for address,
control, and clock signals are recommended.
- Sink or Source DDR Termination
Regulator (LDO) is recommended to generate the VTT supply.
- The Sink or Source DDR Termination
Regulator (LDO) is used to generate the reference voltage VREFCA (VDDS_DDR/2).
- The recommendation is to add decoupling
capacitors for the reference voltage.