Avoid stubs on the high-speed USB signals because they cause signal reflections. If a stub is unavoidable, then

the stub should be less than 200 mm.

Route all high-speed USB signal traces over continuous planes (VCC or GND), with no interruptions.

Avoid crossing over anti-etch, commonly found with plane splits.

Due to high frequencies associated with the USB, a printed circuit board with at least four layers is

recommended; two signal layers separated by a ground and power layer as shown in Figure 7-5.

Signal 1

GND Plane

Power Plane

Signal 2

Figure 7-5. Four-Layer Board Stack-Up

The majority of signal traces should run on a single layer, preferably Signal 1. Immediately next to this layer

should be the GND plane, which is solid with no cuts. Avoid running signal traces across a split in the ground or

power plane. When running across split planes is unavoidable, sufficient decoupling must be used. Minimizing

the number of signal vias reduces EMI by reducing inductance at high frequencies. For more information on

layout guidelines, see High Speed Layout Guidelines and USB 2.0 Board Design and Layout Guidelines.

7.4.2 Layout Example

1

2

3

4

1D-

2D-

9

S

VCC

D+

OE

LEGEND

VIA to Power Plane

VIA to GND Plane

Polygonal Copper Pour

8

7

6

Bypass Capacitor

V+

5

D-

10

2D+

GND

1D+

To Microcontroller

To Microcontroller

To USB Host

USB Port 1

USB Port 2

Figure 7-6. Package Layout Diagram

www.ti.com

TS3USB221E

SCDS263E – SEPTEMBER 2009 – REVISED JULY 2024

Copyright © 2024 Texas Instruments Incorporated

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