Genesys GL3520 - Differential Pairs Trace

USB 3.0 Hub Design Guide
© 2015 Genesys Logic, Inc. - All rights reserved. Page 7
GLI Confidential
2.2 PCB Layer and Material
2.2.1 4-Layer PCB
Four (4) layers and FR4 PCB are recommended to use. Besides, the traces of differential signals must be
entirely routed over ground plane.
PCB Layer
Trace Net Name
Top
SS Differential Pair Trace (Hub IC should be placed in the same layer)
Inner 1
GND
Inner 2
POWER,GND
Bottom
HS Difference Pair , Control Signal
2.2.2 2-Layer PCB
PCB Layer
Trace Net Name
Top
SS Differential Pair Trace (Hub IC should be placed in the same layer)
Bottom
HS Difference Pair , Control Signal
2.3 Differential Pairs Trace
2.3.1 Differential Pair Impedance
The differential impedance requirement must be 90 Ohm ± 10 % and trace width / spacing may be different
by PCB material characteristic base on PCB Vendor suggest.
2.3.2 Differential Trace
Keep the trace length of SS TX/RX or HS D+/D- from USB connector to chip as short as possible. And the
differential pairs trace routing must be symmetrical. USB 3.0 & USB 2.0 differential trace MUST use different
layer to avoid cross routing. Make the differential signal trace GND plane via holes as more as possible to keep
GND plane solid with adjacent GND layer.
2.3.3 Differential Trace Length Preliminary Guidelines
Differential Pairs
Signal Referencing
Trace Mismatch Tolerance
Maximum Total Length
USB 3.0
SSTXP/N, SSRXP/N
Ground
≦5mil
9 inches
USB 2.0
DP/DM
Ground
≦50mil
9 inches