DS2148 datasheet(53/75 Pages) DALLAS

53 / 75 page

DS2148/Q48

53 of 75

PROTECTED INTERFACE USING EXTERNAL RECEIVE TERMINATION

Figure 9-3

NOTES:

1) All resistor values are ±1%.

2) C1 = 0.1µF.

3) S is a 6V transient suppresser.

4) D1 to D4 are Schottky diodes.

5) The fuses are optional to prevent AC power line crosses from compromising the transformers.

6) Rp resistors exist to keep the Fuses from opening during a surge. If they are used, then Rr must be

adjusted to match the line impedance.

7) Rr = 37.5

W for 75W, 60W for 120W E1 systems, or 50W for 100W T1 lines.

8) The Rt resistors are used to increase the transmitter return loss (Table 9-1). No return loss is required

for T1 applications.

9) The transmit transformer turns ratio (N) would be 1:1.36 for 5V operation.

10) The 68

mF is used to keep the local power plane potential within tolerance during a surge.

RTIP

RRING

TTIP

TRING

Receive

Line

N:1

(larger winding

toward the network)

DS2148

0.47µF

(non-

polarized)

VDD (21)

VSS (22)

VDD (36)

VSS (35)

2.048MHz

(this clock can also

be 1.544MHz for T1

only applications)

MCLK

+VDD

1:1

0.1µF

470

Fuse

(optional)

Transmit

Line

Fuse

(optional)

0.1µF

+VDD

0.01µF

68µF

10µF

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