Usb Transmission Line - Renesas RZ/A Series Manuallines

RZ/A1

2. USB Transmission Line

The USB transmission line indicates the wiring pattern that connects the USB connector and the USB
transceiver.
USB2.0 has High-Speed, Full-Speed, and Low-Speed communication modes. High-Speed has a
communication speed of 480 Mbps, so it is necessary to design the USB transmission line as a high
frequency circuit. Impedance control is necessary for a USB transmission line.
Notes on designing the USB transmission line pattern wiring are described below.
• The characteristic impedance required in USB High-Speed transmission lines is a differential impedance
of 90 Ω ± 15 %.
• The impedance control requires different pattern width and pattern interval according to board thickness,
material, and layer configuration. For details, consult the board manufacturer.
• USB module of RZ/A1 incorporates the terminating resistor for the D+ and D- signals during high-speed
operation and the output resistor for the signals during full-speed operation. Therefore, do not place an
external resistor on the transmission line.
• The USB transmission line wiring pattern length from RZ/A1 to the USB connector must be designed so
that it does not exceed the maximum delay time specified in the USB standard. In addition, taking into
account the quality of waveforms during High-Speed, shorter wiring is recommended. Table 2.1 shows
the USB transmission line pattern design values taking the maximum delay times into account for print
wiring boards using general materials.
Table 2.1 USB transmission line pattern design values in consideration of the maximum delay times
Host controller
Function controller
Note: *1. This example is for 100 ps/cm wiring delay.
• The lower layer of the USB transmission lines must be a ground plane. The ground plane must be at least
1 mm wider than the USB transmission lines. The power supply for the ground plane is USBDPVss
• Do not allocate other signal lines near the USB transmission lines. In particular, separate lines for signals
with heavily fluctuating, such as clock or a data bus away from the USB transmission lines. Ensure that
the USB transmission lines do not intersect lines for other signals.
• It is recommended to create a guard ring using the USBDPVss
by 3 times (or more) the D+/D- wiring spacing on the same layer (surface layer) as the USB transmission
line.
• USB transmission lines should be allocated on the same layer without vias. Also, USB transmission line
wiring should not be branched.
• The USB transmission lines should be wired with uniform spaces.
• Separate the USB transmission lines away from oscillators, power supply circuits and any other I/O
connectors.
• USB transmission lines should be wired as straight as possible. If a USB transmission line must turn
within the layout, use a gentle turn of 135° or a circular arc. Do not use sharp angles (right angles) for the
USB transmission lines.
Figure 2.1 shows an example of USB transmission line pattern design when used as a host controller, Figure
2.2 shows an example of USB transmission line pattern design when used as a function controller, Figure
2.3 shows an example of spacing between USB transmission line and ground guard ring.
Note: *1. This is Vss in the BGA package.
R01AN5119EJ0120 Rev.1.20
May.26.20
Guidelines for High-Speed USB2.0 Board Design
Maximum Delay Time
(USB standard)
3 ns
1 ns
Wiring Length *1
300 mm or less
100 mm or less
for the USB transmission line separated
*1
Difference in D+, D-
Wiring Length
2.5 mm or less
2.5 mm or less
.
*1
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