11.1 Layout Guidelines

• The 100-nF capacitors on the TXP and SSTXN nets must be placed close to the USB connector (Type A, Type B, and so forth).
• The ESD and EMI protection devices (if used) must also be placed as close as possible to the USB connector.
• Place voltage regulators as far away as possible from the differential pairs.
• In general, the large bulk capacitors associated with each power rail must be placed as close as possible to the voltage regulators.
• TI recommends that small decoupling capacitors for the 1.8-V power rail be placed close to the TUSB551 as shown below.
• The SuperSpeed differential pair traces for RXP/N and TXP/N must be designed with a characteristic impedance of 90 Ω ±10%. The PCB stack-up and materials determine the width and spacing needed for a characteristic impedance of 90 Ω.
• The SuperSpeed differential pair traces must be routed parallel to each other as much as possible. TI recommends the traces be symmetrical.
• In order to minimize crosstalk, TI recommends keeping high-speed signals away from each other. Each pair must be separated by at least 5 times the signal trace width. Separating with ground also helps minimize crosstalk.
• Route all differential pairs on the same layer adjacent to a solid ground plane.
• Do not route differential pairs over any plane split.
• Adding test points causes impedance discontinuity and therefore negatively impacts signal performance. If test points are used, they must be placed in series and symmetrically. They must not be placed in a manner that causes stub on the differential pair.
• Avoid 90 degree turns in traces. The use of bends in differential traces must be kept to a minimum. When bends are used, the number of left and right bends must be as equal as possible and the angle of the bend must be ≥ 135 degrees. This minimizes any length mismatch caused by the bends and therefore minimize the impact bends have on EMI.
• Match the etch lengths of the differential pair traces. There must be less than 5-mils difference between a SS differential pair signal and its complement. The USB 2.0 differential pairs must not exceed 50-mils relative trace length difference.
• The etch lengths of the differential pair groups do not need to match (that is, the length of the RXP/N pair to that of the TXP/N pair), but all trace lengths must be minimized.
• Minimize the use of vias in the differential pair paths as much as possible. If this is not practical, make sure that the same via type and placement are used for both signals in a pair. Any vias used must be placed as close as possible to the TUSB551 device.
• To ease routing, the polarity of the SS differential pairs can be swapped. This means that TXP can be routed to TXN or RXN can be routed to RXP.
• Do not place power fuses across the differential pair traces.

11.2 Layout Example

SN65LVPE512 USB3.0 signals routing with embedded Host and Std. Type A connector

Figure 38. SN65LVPE512 USB3.0 Signals Routing With Embedded Host and Std. Type A Connector