LTC2845 datasheet(13/20 Pages) LINER

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LTC2845

sn2845 2845fs

APPLICATIONS INFORMATION

Figure 16. Typical V.28 Interface

GENERATOR

BALANCED

INTERCONNECTING

CABLE

LOAD

CABLE

TERMINATION

RECEIVER

2845 F16

Figure 17. V.28 Receiver Configuration

20k

LTC2845

RECEIVER

2845 F17

10k

20k

GND

V.28 (RS232) Interface

A typical V.28 unbalanced interface is shown in Figure 16.

A V.28 single-ended generator output A with ground C is

connected to a single-ended receiver with input A

' con-

nected to A, ground C

' connected via the signal return

ground C.

In V.28 mode, all switches are off except S3 inside the

LTC2846/LTC2845 which connects a 6k (R8) impedance

to ground in parallel with 20k (R5) plus 10k (R6) for a

combined impedance of 5k as shown in Figure 17. The

noninverting input is disconnected inside the LTC2846/

LTC2845 receiver and connected to a TTL level reference

voltage for a 1.4V receiver trip point.

V.35 Interface

A typical V.35 balanced interface is shown in Figure 18. A

V.35 differential generator with outputs A and B with

Figure 19. V.35 Receiver Configuration

Figure 18. Typical V.35 Interface

GENERATOR

BALANCED

INTERCONNECTING

CABLE

LOAD

CABLE

TERMINATION

RECEIVER

2845 F18

Ω

125

Ω

125

Ω

124

Ω

20k

LTC2846

RECEIVER

2845 F19

51.5

Ω

51.5

Ω

10k

GND

20k

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 LTC2846

are on, connecting the T network impedance as shown in

Figure 19. 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.

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 as

shown in Figure 20.

LTC2845 Datasheet(PDF) 13 Page - Linear Technology

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