9 Power Supply Recommendations

The TMUXHS221 does not require a power supply sequence. However, TI recommends that the device is

enabled after VCC is stable and in specification. TI also recommends to place ample decoupling capacitors at

the device VCC near the pin.

10 Layout

10.1 Layout Guidelines

Place supply bypass capacitors as close to the VCC pin as possible. Avoid placing the bypass capacitors

near the D+/D–traces. The high-speed D+/D– traces should always be matched and must be no more than

4 inches, 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 the layout, the impedance

of D+ and D– traces should match the cable characteristic differential impedance for optimal performance.

Route the high-speed USB signals using a minimum of vias and corners which will reduce 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

IC’s 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 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 split.

For high speed layout guidelines, refer to High-Speed Layout Guidelines for Signal Conditioners and USB Hubs

application note.

10.2 Layout Example

Figure 10-1 shows TMUXHS221 layout example.

Figure 10-1. TMUXHS221 Layout Example

www.ti.com

TMUXHS221

SLASF52 – AUGUST 2022

Copyright © 2022 Texas Instruments Incorporated

Submit Document Feedback

13

Product Folder Links: TMUXHS221