
Hardware Design Guide
69
IXP28XX Network Processor
QDR SRAM
Figure 31
illustrates the routing for QDR D signal trace width/spacing.
Table 22
lists the QDR D stack-up signal cross-section details.
Table 21.
QDR D Signal Group Routing Guidelines
Parameter
Routing Guideline
Signal Group
D
Topology
Daisy Chain or Matched-T topology
Reference Plane
Ground
Characteristic Trace Impedance
50
Ω
±10%
RTT
50
Ω
±1%
Nominal Trace Width
5 mils
Nominal Trace Separation
8 - 15 mils
Group Spacing
Isolation from all other signals is 20 mils.
Trace length P
1
+A to SRAMs
1.
P refers to the package length.
Should be matched to K-Clk trace length minus 0.5 inches.
Maximum = 11.0 inches
Trace length B
As short as possible.
Maximum = 0.4 inches
Trace length C
Maximum = 0.5 inches
Trace length D
As short as possible; Maximum = 1.0 inch
Maximum via count per signal
As small as possible; Maximum = 7 vias
Length tuning method
All D signals matched within ±25 mils, where length includes
package length compensation (P+A)
Figure 31.
QDR D Signal Trace Width/Spacing Routing
B3992-01
20 mil or larger
Prepreg
S
W
W
Other
Signals
POWER or GND Plane
POWER or GND Plane
T
d2
T
d1
T
signal
DATA
Signal
DATA
Signal
D2
D1
Table 22.
QDR D Stack-up Signal Cross-section Details
Parameter
QDR
Signal
Trace
Width (W)
[mils]
Trace
Thickness
(Tsignal)
[mils]
Trace
Spacing
(S) [mils]
D1
Thickness
(TD1)
[mils]
D2
Thickness
(Td2)
[mils]
Er(D1) Er(D2)
Spacing
between
signal
groups
[mils]
Value
D
5
0.5
8 - 15
5.0
5.7
3.5
3.8
20 - 25
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