TS3USB3000

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SCDS337B – DECEMBER 2012 – REVISED DECEMBER 2015

Typical Application (continued)

9.2.3.1 USB 2.0 Eye Pattern

Figure 32. 480-Mbps USB 2.0 Eye Pattern With No Device

Figure 33. 480-Mbps USB 2.0 Eye Pattern for USB Switch

10 Power Supply Recommendations

Power to the device is supplied through the VCC pin and must follow the USB 1.0, 1.1, and 2.0 standards. TI

recommends placing a bypass capacitor as close to the supply pin VCC as possible to help smooth out lower

frequency noise to provide better load regulation across the frequency spectrum.

11 Layout

11.1 Layout Guidelines

Place supply bypass capacitors as close to VCC pin as possible and avoid placing the bypass caps near the

D+/D– traces.

The high-speed D+/D- must match and be no more than 4 inches long; otherwise, the eye diagram performance

may be degraded. A high-speed USB connection is made through a shielded, twisted pair cable with a differential

characteristic impedance. In layout, the impedance of D+ and D– traces must match the cable characteristic

differential impedance for optimal performance.

Route the high-speed USB signals using a minimum of vias and corners which reduces signal reflections and

impedance changes. When a via must be used, increase the clearance size around it to minimize its

capacitance. Each via introduces discontinuities in the signal’s transmission line and increases the chance of

picking up interference from the other layers of the board. Be careful when designing test points on twisted pair

lines; through-hole pins are not recommended.

When it becomes necessary to turn 90°, use two 45° turns or an arc instead of making a single 90° turn. This

reduces reflections on the signal traces by minimizing impedance discontinuities.

Do not route USB traces under or near crystals, oscillators, clock signal generators, switching regulators,

mounting holes, magnetic devices or ICs that use or duplicate clock signals.

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

the stub must be less than 200 mm.

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

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

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