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LTC1343

APPLICATIONS INFORMATION

Figure 19. V.28 Receiver Configuration

Figure 21. V.35 Receiver Configuration

The generator differential impedance must be 50

Ω to

150

Ω and the impedance between shorted terminals (A

and B) and ground C must be 150

Ω ±15Ω. For the

generator termination, switches S1 and S2 are both on and

the top side of the center resistor is brought out to a pin so

it can be bypassed with an external capacitor to reduce

common mode noise as shown in Figure 22.

Any mismatch in the driver rise and fall times or skew in

the driver propagation delays will force current through

the center termination resistor to ground, causing a high

frequency common mode spike on the A and B terminals.

The common mode spike can cause EMI problems that are

reduced by capacitor C1 which shunts much of the com-

mon mode energy to ground rather than down the cable.

V.35 Interface

A typical V.35 balanced interface is shown in Figure 20. A

V.35 differential generator with outputs A and B with

ground C is connected to a differential receiver with

ground C

', inputs A' connected to A, B' connected to B. The

V.35 interface requires a T or delta network termination at

the receiver end and the generator end. The receiver

differential impedance measured at the connector must be

100

Ω ±10Ω, and the impedance between shorted termi-

nals (A

' and B) and ground C' must be 150

Ω ±15Ω.

In V.35 mode, both switches S1 and S2 inside the LTC1344

are on, connecting the T network impedance as shown in

Figure 21. Both switches in the LTC1343 are off. The 30k

input impedance of the receiver is placed in parallel with

the T network termination, but does not affect the overall

input impedance significantly.

Figure 20. Typical V.35 Interface

Figure 22. V.35 Driver Using the LTC1344

124

Ω

20k

LTC1344

LTC1343

RECEIVER

1343 F19

51.5

Ω

51.5

Ω

10k

GND

20k

124

Ω

20k

LTC1344

LTC1343

RECEIVER

1343 F21

51.5

Ω

51.5

Ω

10k

GND

20k

GENERATOR

BALANCED

INTERCONNECTING

CABLE

LOAD

CABLE

TERMINATION

RECEIVER

1343 F20

Ω

125

Ω

125

Ω

V.35 DRIVER

51.5

Ω

1343 F22

51.5

Ω

LTC1344

124

Ω

100pF

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