XRT83SL314IB datasheet(21/85 Pages) EXAR

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XRT83SL314

14-CHANNEL T1/E1/J1 SHORT-HAUL LINE INTERFACE UNIT

PRELIMINARY

REV. P1.0.5

2.1.2

CASE 2: Internal Termination With One External Fixed Resistor for All Modes

Along with the internal termination, a high precision external fixed resistor can be used to optimize the return

loss. This external resistor can be used for all modes of operation ensuring one bill of materials. There are

three resistor values that can be used by setting the RxRES[1:0] bits in the appropriate channel register.

Selecting the value for the external fixed resistor is shown in Table 3.

By default, RxRES[1:0] is set to "None" for no external fixed resistor. If an external fixed resistor is used, the

XRT83SL314 uses the parallel combination of the external fixed resistor and the internal termination as the

input impedance. See Figure 5 for a typical connection diagram using the external fixed resistor.

NOTE: Without the external resistor, the XRT83SL314 meets all return loss specifications. This mode was created to add

flexibility for optimizing return loss by using a high precision external resistor.

FIGURE 5. TYPICAL CONNECTION DIAGRAM USING ONE EXTERNAL FIXED RESISTOR

TABLE 3: SELECTING THE VALUE OF THE EXTERNAL FIXED RESISTOR

RXRES[1:0]

EXTERNAL FIXED RESISTOR

0h (00)

None

1h (01)

240

Ω

2h (10)

210

Ω

3h (11)

150

Ω

TIP

RING

XRT83SL314 LIU

1:1

Internal Impedance

Line Interface T1/E1/J1

R=240

Ω, 210Ω, or 150Ω

Receiver

Input

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