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Universal Serial Bus (USB) Interface—Intel
12.2.2.2
USB 2.0 Trace Length Pair Matching
USB 2.0 signal pair traces must be trace length matched. The maximum trace length
mismatch within a USB 2.0 signal pair must be no greater than 60 mils.
12.2.2.3
USB 2.0 Trace Length Guidelines
Use the following trace length guidelines.
Table 63.
USB 2.0 Trace Length Guidelines
Topology
Back Panel
Front Panel
Notes:
1.
The numbers in
a. An approximate 1:1 trade-off can be assumed for the motherboard trace length vs. the daughter
card trace length (e.g., trade 1 inch of daughter card trace length for 1 inch of motherboard trace
length).
b. The trace length on front panel daughter card has a maximum trace length of 2 inches.
c. USB twisted-pair shielded cable as specified in the USB 2.0 Specification was used.
2.
For front panel solutions, signal matching is considered from EP80579 to the front panel header.
12.2.3
USB_RBIASp/USB_RBIASn Connection
Intel recommends designers short the USB_RBIASp and the USB_RBIASn pins at the
package and then route to one end of a 22.6 Ω ±1% resistor to ground. Place the
resistor within 0.50 inch of EP80579. Avoid routing next to clock pins. The following are
the general recommendation for the USB_RBIAS:
• Route on top layer (recommended, not required).
• 50 Ω+/-15% single ended impedance/impedance defines trace width.
• Signals must be Ground referenced.
• Spacing requirements may be reduced to 4mil through the pin/via field.
Figure 114. USB_RBIASp/USB_RBIASn Connection
®
Intel
EP80579 Integrated Processor Product Line
Order Number: 320068-005US
®
EP80579 Integrated Processor Product Line
Motherboard
Motherboard
Cable
Trace Length
Trace Length
Length
Microstrip
(inches)
(inches)
N/A
2–11
6
7
7.5
6
9
5
10.5
4
11
N/A
12
2
Table 63
are based on the following simulation assumptions:
EP80579
USB_RBIASp
USB_RBIASn
Card
Trace
Stripline
Length
(inches)
(inches)
2–10
N/A
7
1.5–2
6
1.5–2
Keep the maximum mismatch within
4
1.5–2
data pairs to less than 60 mils. This
3
1.5–2
2
1.5–2
N/A
1.5–2
22.6 Ω ± 1%
Signal
Matching
is over the entire routing space.
May 2010
169
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