Nvidia Jetson Nano Product Design Manual page 32

Parameter
Trace Spacing (Stripline/Microstrip)
To plane and capacitor pad
To unrelated high-speed signals
Length/Skew
Trace loss characteristic @ 2.5 GHz
Breakout region (max length)
Max trace length/delay
Max PCB via distance from the BGA
PCB within pair (intra-pair) skew
Within pair (intra-pair) matching between subsequent
discontinuities
Differential pair uncoupled length
Via
Via placement
Max # of vias
Max via stub length
Routing signals over antipads
AC Cap
Value
Location (max length to adjacent discontinuity)
Voiding
General: See Chapter 15 for guidelines related to serpentine routing, routing over voids and noise coupling
Notes:
1. The PCIe spec. has 40-60Ω absolute min/max trace impedance, which can be used instead of the 50Ω, ± 15%.
2. If routing in the same layer is necessary, route group TX and RX separately without mixing RX/TX routes and keep distance between nearest TX/RX trace
and RX to other signals 3x RX-RX separation.
3. Longer trace lengths may be possible if the total trace loss is equal to or better than the target. If the loss is greater, the max trace lengths will need to
be reduced.
4. Do length matching before via transitions to different layers or any discontinuity to minimize common mode conversion.
NVIDIA Jetso n Nano
Requirement
pair – pair 3x / 4x
3x / 4x
3x / 4x
< 0.7
41.9
5.5 (880)
41.9
0.15 (0.5)
0.15 (0.5)
41.9
Place GND vias as symmetrically as possible to data pair vias. GND via distance should be placed
less than 1x the diff pair via pitch
PTH vias 2 for TX traces and 2 for RX trace
Micro-vias No requirement
0.4
Not allowed
Min/Max 0.075 / 0.2
8
Voiding the plane directly under the pad 3-4
mils larger than the pad size is
recommended.
USB and PCI Express
Units Notes
Dielectric See Note 2
The following max length is derived based on this
dB/in
characteristic. See Note 3
Minimum width and spacing. 4x or wider
ps
dielectric height spacing is preferred
in (ps)
ps Max distance from BGA ball to first PCB via.
Do trace length matching before hitting
mm (ps)
discontinuities
mm (ps)
ps
mm Longer via stubs would require review
Only required for TX pair when routed to
uF
connector
mm Discontinuity such as edge finger, component pad
See Figure 6-8
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