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TUSB522P

SLLSEV9A – JULY 2016 – REVISED OCTOBER 2016

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Copyright © 2016, Texas Instruments Incorporated

10 Layout

10.1 Layout Guidelines

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RXP/N and TXP/N pairs should be routed with controlled 90-Ω differential impedance (±15%).

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Keep away from other high speed signals.

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Intra-pair routing should be kept to within 2mils.

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Length matching should be near the location of mismatch.

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Each pair should be separated at least by 3 times the signal trace width.

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The use of bends in differential traces should be kept to a minimum. When bends are used, the number of left

and right bends should be as equal as possible and the angle of the bend should be

≥ 135 degrees. This will

minimize any length mismatch causes by the bends and therefore minimize the impact bends have on EMI.

•

Route all differential pairs on the same of layer.

•

The number of VIAS should be kept to a minimum. It is recommended to keep the VIAS count to 2 or less.

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Keep traces on layers adjacent to ground plane.

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Do NOT route differential pairs over any plane split.

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Adding Test points will cause impedance discontinuity; and will therefore, negatively impact signal

performance. If test points are used, they should be placed in series and symmetrically. They must not be

placed in a manner that causes a stub on the differential pair.

•

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.

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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.

10.2 Layout Example

Figure 3. Example Layout