TS3USB3000_15 Datasheet, PDF (17/26 Pages) Texas Instruments – DPDT USB 2.0 High-Speed and Mobile High-Definition Link Switch

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Typical Application (continued)
9.2.3.1 USB 2.0 Eye Pattern
TS3USB3000
SCDS337B – DECEMBER 2012 – REVISED DECEMBER 2015
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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