74
2.7.3 USB2.0 Trace Length Guidelines
Figure 21
: Topology for USB2.0
Table 23
: USB2.0 Trace Length Guidelines
Parameter
Main Route Guidelines
Notes
Signal Group
USB[3:0]+, USB[3:0]-
Differential Impedance Target
85 Ω ±10%
Single End
55Ω ±10%
Spacing between pairs-to-pairs
(inter-pair) (s)
7H
(MS) and
5H
(DS)
1
Spacing between differential
pairs and high-speed periodic
signals
Min. 50 mils
Spacing between differential
pairs and low-speed non
periodic signals
7H
(MS) and
5H
(DS)
1
LA
Please see the SOM-5992 Layout Checklist
LB
Carrier Board Length
Max length of LA+LB
16”
Length matching
Differential pairs (intra-pair): Max.
±2 mils
Reference Plane
GND referencing preferred
Spacing from edge of plane
Min. 40mils
Carrier Board Via Usage
Try to minimize number of vias
Notes:
1.
H is height above reference plane.
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