TDA2SA datasheet(362/427 Pages) TI2

362 / 427 page

Trace

Ferrite Bead

VBUS

USB Socket

SHIELD_GND

GND

+5 V

SHIELD_GND

Ferrite Bead

362

TDA2SX, TDA2SG, TDA2SA

TDA2HG, TDA2HV, TDA2HF, TDA2LF

SPRS951F – DECEMBER 2015 – REVISED MAY 2019

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Product Folder Links: TDA2SX TDA2SG TDA2SA TDA2HG TDA2HV TDA2HF TDA2LF

Applications, Implementation, and Layout

Figure 8-32. USB Connector

8.5.2.2.2.5 Clock Routings

To address the system clock emissions between devices, place a ~10 to 130

Ω resistor in series with the

clock signal. Use a trial and error method of looking at the shape of the clock waveform on a high-speed

oscilloscope and of tuning the value of the resistance to minimize waveform distortion. The value on this

resistor should be as small as possible to get the desired effect. Place the resistor close to the device

generating the clock signal. If an external crystal is used, follow the guidelines detailed in the Selection

and Specification of Crystals for Texas Instruments USB 2.0 Devices (SLLA122).

When routing the clock traces from one device to another, try to use the 3W spacing rule. The distance

from the center of the clock trace to the center of any adjacent signal trace should be at least three times

the width of the clock trace. Many clocks, including slow frequency clocks, can have fast rise and fall

times. Using the 3W rule cuts down on crosstalk between traces. In general, leave space between each of

the traces running parallel between the devices. Avoid using right angles when routing traces to minimize

the routing distance and impedance discontinuities. For further protection from crosstalk, run guard traces

beside the clock signals (GND pin to GND pin), if possible. This lessens clock signal coupling, as shown in

Figure 8-33.

Figure 8-33. 3W Spacing Rule

TDA2SA Datasheet(PDF) 362 Page - Texas Instruments