TSB41BA3FTPFPEP datasheet(18/73 Pages) TI

18 / 73 page

Both the twisted pair A (TPA) and the twisted pair B (TPB) cable interfaces incorporate differential comparators

to monitor the line states during initialization and arbitration when connected to a 1394a-2000-compliant device.

The outputs of these comparators are used by the internal logic to determine the arbitration status. The TPA

channel monitors the incoming cable common-mode voltage. The value of this common-mode voltage is used

during 1394a-mode arbitration and sets the speed of the next packet transmission. In addition, the TPB channel

monitors the incoming cable common-mode voltage on the TPB pair for the presence of the remotely supplied

twisted pair bias (TPBIAS) voltage.

When connected to a 1394a-2000-compliant node, the TSB41BA3F-EP provides a 1.86-V nominal bias voltage

at the TPBIAS terminal for port termination. The PHY contains three independent TPBIAS circuits (one for each

port). This bias voltage, when seen through a cable by a remote receiver, indicates the presence of an active

connection. This bias voltage source must be stabilized by an external filter capacitor of 1 μF.

The line drivers in the TSB41BA3F-EP are designed to work with external 112-Ω termination resistor networks in

order to match the 110-Ω cable impedance. One termination network is required at each end of a twisted-pair

cable. Each network is composed of a pair of series-connected ~56-Ω resistors. The midpoint of the pair of

resistors that is connected to the TPA terminals is connected to its corresponding TPBIAS voltage terminal. The

midpoint of the pair of resistors that is directly connected to the TPB terminals is coupled to ground through a

parallel RC network with recommended values of 5 kΩ and 270 pF. The values of the external line-termination

resistors are designed to meet the standard specifications when connected in parallel with the internal receiver

circuits. A precision external resistor connected between the R0 and R1 terminals sets the driver output current,

along with other internal operating currents.

When the power supply of the TSB41BA3F-EP is off while the twisted-pair cables are connected, the

TSB41BA3F-EP transmitter and receiver circuitry present a high-impedance signal to the cable that does not

load the device at the other end of the cable.

When the TSB41BA3F-EP is used without one or more of the ports brought out to a connector, the twisted-pair

terminals of the unused ports must be terminated for reliable operation. For each unused port, the preferred

method is for the port to be forced to the 1394a-only mode (data-strobe-only mode, DS), then the TPB+ and

TPB– terminals can be tied together and then pulled to ground; or the TPB+ and TPB– terminals can be

connected to the suggested normal termination network. The TPA+ and TPA– terminals of an unused port can

be left unconnected. The TPBIAS#_SD# terminal can be left unconnected.

If the port is left in bilingual (Bi) mode, then the TPB+ and TPB– terminals can be left unconnected or the TPB+

and TPB– terminals can be connected to the suggested normal termination network. The TPA+ and TPA–

terminals of an unused port can be left unconnected. The TPBIAS#_SD# terminal can be left unconnected.

If the port is left in a forced 1394b Beta-only (B1, B2, or B4) mode, then the TPB+ and TPB– terminals can be

left unconnected or the TPB+ and TPB– terminals can be connected to the suggested normal termination

network. The TPA+ and TPA– terminals of an unused port can be left unconnected. The TPBIAS#_SD# terminal

must be pulled to ground through a 1.2-kΩ or smaller resistor.

To operate a port as a 1394b bilingual port, the speed/mode selections terminals (S5_LKON, S4, S3, S2_PC0,

S1_PC1, and S0_PC2) need to be pulled to VCC or ground through a 1-kΩ resistor. The port must be operated in

the 1394b bilingual mode whenever a 1394b bilingual or a 1394b Beta-only connector is connected to the port.

To operate the port as a 1394a-only port, the speed/mode selection terminals must be configured correctly to

force 1394a-2000-only operation on that port. The only time the port must be forced to the data-strobe-only

mode is if the port is connected to a 1394a connector (either 6-pin, which is recommended, or 4-pin). This mode

is provided to ensure that 1394b signaling is never sent across a 1394a cable.

Note

A bilingual port can only connect to a 1394b-only port that operates at S400b. It cannot establish a

connection to a S200b or S100b port. A port that has been forced to S400b (B4) can connect to a

1394b-only port at S400b (B4) or S200b (B2) or S100b (B1). A port that has been forced to S200b can

connect to a 1394b-only port at S200b or S100b. A port that has been forced to S100b can only

connect to a 1394b-only port at S100b.

TSB41BA3F-EP

SLLSFA1 – SEPTEMBER 2020

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