TSB17BA1

IEEE STD 1394b SINGLEPORT CABLE TRANSCEIVER

SLLS568C − JANUARY 2004 − REVISED MARCH 2004

10

POST OFFICE BOX 655303

APPLICATION INFORMATION

cable connection (continued)

This also works for CAT5-structured wiring cable that is typically installed in a home or office. The CAT5 cables

in these structured wiring installations are wired straight through and do not crossover. It is recommended that

the structured wiring hub at the center of the star-type installation contain only straight-through wiring. If the

RJ45 connector is brought outside the wall, then it also is connected straight through. If all networkable devices

are also created as straight-through connections, then the required crossover is implemented when the

networkable device is connected to the RJ45 wall-plate connection using a crossover cable.

There is a special case for the structured wiring if the wall plate enables a 4-pin, 6-pin, or 9-pin 1394b connector.

In this case, one port of the 1394b PHY is connected to the 1394b connector in the typical manner. However,

the connection between the 1394b PHY and the UTP5 connection inside the wall must implement a crossover.

This is true if the 1394b-structured wiring hub is wired straight through and the cable pulled is straight through.

In this case, since all the electrical connections between the two 1394b ports are straight through, the crossover

must be implemented on the wall-plate UTP5 connection. It is required that this crossover be completed

between the RJ45 connector on the wall plate and the isolating transformer of the termination network.

Please contact Texas Instruments for further detail.

PCB layout considerations

There are certain signals that require special care in the layout of the TSB17BA1. The UTP5_INP and

UTP5_INN signals are the inputs from what might be a 100-m cable. After propagating through a cable this long

the signal amplitudes could be small and more easily affected by board noise. The routing for these signals from

the RJ45 connector through the termination network to the PHY must be short and, if possible, a ground guard

etch must be implemented to protect them from board noise. This etch must extend the length of the traces,

be far enough away from the signal traces not to significantly affect the trace impedance, and be connected to

the ground plane every 2 cm or less.

The precision resistor between the R1 and R0 terminals sets the internal currents and voltages of the

TSB17BA1. Any noise that couples onto the R1 terminal can affect the entire device. Therefore, this connection

must be kept short and as close to the TSB17BA1 as possible. This connection can also benefit from a ground

guard etch around the R1 and R0 terminal connections.

To keep the noise introduced to these signals to a minimum it is recommended that no digital signals or large

amplitude analog signals (like switching regulators) be routed in the vicinity of terminals 19−22 on the

TSB17BA1. The output signals of the TSB17BA1 (UTP5_OUTP, UTP5_OUTN, BETA_OUTP, and

BETA_OUTN) must also be routed away from these sensitive input pins.