86
Memory Controller
Table 44.
Control Signals Routing Guidelines
Parameter
Routing Guideline
Reference Plane
Route over unbroken ground plane is preferred.
(Refer to Table for alternatives if this is not feasible).
Preferred Topology
Micro-strip only for Un-buffered memory
configurations
Either Micro-strip or Stripline for Buffered DIMMs and
lightly loaded Un-buffered DIMMs (i.e. single bank or
dual bank w/ less than or equal to 36pF input
capacitance).
Breakout Trace WIdth and Spacing
5 mils x 5 mils acceptable through pin field and
terminations
Trace Impedance
•
45 ohms Motherboard/Add-in card impedance
•
50 ohms Motherboard/Add-in Card Impedance
Strip Line Trace Spacing (edge to edge)
•
Spacing within group 12 mils minimum
•
5 mils acceptable through pin field and
terminations
•
> 20 mils from the Clock/DQ/DQS groups
Series Resistor Rs
No series termination required
Parallel Resistor Rp
51.1 +/- 5% ohms
OR
Split termination of 100 ohms +/- 5% terminated to
2.5V and 100 ohms +/- 5% terminated to ground
Place Vtt terminations in a Vtt island after the DIMM
Package Trace Length:
Breakout Trace Length (TL1):
Lead-in to Connector Trace Length (TL2):
Parallel Termination Route Length (TL3):
See
for package net length report and
≤
0.5”
2.0” to 9.0”
0.15” to 0.5”
Length Matching Requirements:
The package lengths from Die to Ball provided in
must be accounted for when length matching
For total capacitive loads greater than 36pF, all
ADD/CMD/CTRL trace lengths must be 2.0” to 3.0”
shorter than M_CK’s trace length
For total capacitive loads less than or equal to 36pF,
all ADD/CMD/CTRL trace lengths must be 1.0” to 3.0”
shorter than M_CK’s trace length
Routing Guideline 1
Route these signals on the same layer as the M_CKs.
Routing Guideline 2
Minimize layer changes (two vias or less)
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