TDA2SA datasheet(363/427 Pages) TI2

363 / 427 page

Power Pins

USB PHY

0.1 µF

0.001 µF

XTAL

363

TDA2SX, TDA2SG, TDA2SA

TDA2HG, TDA2HV, TDA2HF, TDA2LF

www.ti.com

SPRS951F – DECEMBER 2015 – REVISED MAY 2019

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Product Folder Links: TDA2SX TDA2SG TDA2SA TDA2HG TDA2HV TDA2HF TDA2LF

Applications, Implementation, and Layout

8.5.2.2.2.6 Crystals/Oscillator

Keep the crystal and its load capacitors close to the USB PHY pins, XI and XO (see Figure 8-34). Note

that frequencies from power sources or large capacitors can cause modulations within the clock and

should not be placed near the crystal. In these instances, errors such as dropped packets occur. A

placeholder for a resistor, in parallel with the crystal, can be incorporated in the design to assist oscillator

startup.

Power is proportional to the current squared. The current is I = C*dv/dt, because dv/dt is a function of the

PHY, current is proportional to the capacitive load. Cutting the load to 1/2 decreases the current by 1/2

and the power to 1/4 of the original value. For more details on crystal selection, see the Selection and

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

Figure 8-34. Power Supply and Clock Connection to the USB PHY

8.5.2.2.2.7 DP/DM Trace

Place the USB PHY as close as possible to the USB 2.0 connector. The signal swing during high-speed

operation on the DP/DM lines is relatively small (400 mV ± 10%), so any differential noise picked up on

the twisted pair can affect the received signal. When the DP/DM traces do not have any shielding, the

traces tend to behave like an antenna and picks up noise generated by the surrounding components in

the environment. To minimize the effect of this behavior:

•

DP/DM traces should always be matched lengths and must be no more than 4 inches in length;

otherwise, the eye opening may be degraded (see Figure 8-35).

•

Route DP/DM traces close together for noise rejection on differential signals, parallel to each other and

within two mils in length of each other. The measurement for trace length must be started from

device's balls.

•

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

characteristic impedance of 90

Ω ±15%. In layout, the impedance of DP and DM should each be 45 Ω

± 10%.

•

DP/DM traces should not have any extra components to maintain signal integrity. For example, traces

cannot be routed to two USB connectors.

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