Advantech EVA-X4300, User Manual

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EVA-X4300 System Design Guide 22
7. The common-mode choke used ( if really necessary ) on the DP and DM lines
must be placed as close as possible to the USB connector and must have
Z
com
< 8 Ω @ 100 MHz and Z
diff
< 300 Ω @ 100 MHz.
8. The analog power pins of EVA-X4300, AVDD0/1/2/3 and AVDDPLL0/1, need to
be properly filtered for USB performance.
9. It is recommended to connect the analog ground pins of EVA-X4300, AVSS0/1/
2/3 and AVSSPLL0/1, to an isolated (quiet) analog ground plane, which is con-
nected to the digital ground plane with a single “Bridge” or Ferrite Bead. Please
refer to section 2.4 for more details.
10. Place the external resistors of REXT0/1, pin U26 & P26, as close to the EVA-
X4300 as possible. And connect another ends of these external resistors to the
isolated analog ground plane described above.
11. Do not run any high-speed signal close to the external resistors of REXT0/1 to
keep from interference and coupling.
12. Provide a good path from the USB connector shell to the chassis ground.
13. Maintain the maximum possible distance between Hi-Speed USB differential
pairs, high-speed or lows-peed clock, and non-periodic signals. The minimum
recommended distances are as follows:
!
20 mils between the DP and DM traces and low-speed non-periodic signal
traces.
! 50 mils between the DP and DM traces and clock/high-speed periodic signal
traces.
!
20 mils between two pairs of the DP and DM traces.
14. USB data lines must be routed as “ critical signals ”. Locate the USB connector
close to EVA-X4300. The DP and DM signals in a pair must be routed in parallel
to each other. Do not route these traces near high frequency signals. Guard
ground traces on each side of the signal pair can minimize the induced common
mode noise.
15. Ferrite beads and decoupling capacitor placed on VBUS are for EMI purposes,
thus these components should be placed close to the USB connectors. A value
of about 150 µF/10 V for the decoupling capacitor is recommended on each
port.