Marvell ARMADA 88F6810 Hardware Design Manual page 138

88F6810, 88F6820 and 88F6828
Hardware Design Guide
Table 45: Routing Constraints when Configured as a Device (Continued)
Par a meter
Opposite direction near-end crosstalk
Opposite direction lane separation
(micro-strip with GND shield)
Same direction far-end crosstalk
Same direction lane separation
(micro-strip with GND shield)
USB3-other crosstalk
TL1+TL2+TL3+TL4, TL6 inner pair skew
R1
TL[x] differential impedance
TL[x] common mode impedance
Common mode choke parameters
ESD diodes parasitic capacitance
C1
NOTES:
1. Target impedance should be 90 ohm differential; any mismatch should be taken as a part of the loss.
2. Derived from the loss value by calculation with 0.5 dB/inch @ Fbaud/2 when using a common mode
choke with 1dB loss and ESD protection diodes with 0.3pF parasitic capacitance with no stubs on the
USB traces.
3. In the USB routing, it is essential to avoid capacitive discontinuities and via through-hole long stubs.
Via stubs can occur on vias or on the USB connector pins. For further information refer to the
Section 2, Generic Guidelines for SERDES Interfaces, on page
4. Discontinuities, such as capacitive type, can cause significant insertion loss degradation, causing the
assumption, taken as loss per inch, to be smaller than actual.
5. The maximal allowed trace length can vary according to the material and geometrical characteristics.
6. Common mode choke and ESD protection diodes are optional. When used, it is essential to choose
devices that are designed for USB 3.0 and to consider the effect on the impedance, crosstalk, and loss
parameters. It is recommended to use devices that do not create a stub on the USB traces.
7. The allowed crosstalk is highly dependent on the aggressor's waveform (rise time and swing). The
recommended crosstalk value should account for all common aggressor types. The recommended
separation value is for an aggressor of the same type of interface.
8. Rx summary crosstalk should include all possible aggressors, assuming Rx sensitivity is compliant
with the USB 3.0 specifications.
9. The crosstalk is calculated for max[(Fbaud/2),(0.35/Trise)] of the aggressor interface.
10. The separation is calculated assuming the same type of SERDES and typical board layer stack-up.
Make certain to verify that the crosstalk limitation is met in each specific system.
11. The separation value is calculated for a single-ended impedance of 47 ohm, a differential impedance
of 90 ohm, micro-strip trace length coupled along the entire end-to-end path, and a dielectric loss
coefficient of 0.027. If the loss coefficient is lower, a higher separation may be required.
12. For GND shield guidelines refer to device Board Recommendations section.
13. Skew parameters should include package traces lengths. Refer to the device hardware specifications
for specific package trace length information.
14. Use R1 and R2 to divide the Vbus actual voltage to the Vbus control MPP operating voltage. Refer to
the device hardware specifications for the allowed voltage on the specific MPP input pin and calculate
R1 and R2 accordingly.
15. It is essential to use high-speed, low-ESL, low-ESR capacitors.
Doc. No. MV-S302310-U0 Rev. A
Page 128
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75 100 200
Document Classification: Public
Tol e r a n c e Units N o te s
/ S k e w
dB
Signal 7, 10, 11,
width 12
dB 9
Signal 7, 10, 11,
width 12
dB
mil 13
ohm 14
+-10% ohm
ohm
6
pF 6
nF 15
9.
Copyright © 2017 Marvell
August 30, 2017