12
LTC1543
sn1534 1543fas
APPLICATIO S I FOR ATIO
WUUU
V.28 (RS232) Interface
A typical V.28 unbalanced interface is shown in Figure 17.
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
LTC1543/LTC1544 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 18. The
noninverting input is disconnected inside the LTC1543/
LTC1544 receiver and connected to a TTL level reference
voltage for a 1.4V receiver trip point.
Figure 17. Typical V.28 Interface
AA
'
CC
'
GENERATOR
BALANCED
INTERCONNECTING
CABLE
LOAD
CABLE
TERMINATION
RECEIVER
1543 F17
Figure 18. V.28 Receiver Configuration
V.35 Interface
A typical V.35 balanced interface is shown in Figure 19. 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
100Ω␣ ±10Ω, and the impedance between shorted termi-
nals (A' and B') and ground C' must be 150Ω ±15Ω.
In V.35 mode, both switches S1 and S2 inside the LTC1344A
are on, connecting the T network impedance as shown in
Figure 20. The switch in the LTC1543 is off. The 30k input
A
A
'
B
C
B
'
C
'
GENERATOR
BALANCED
INTERCONNECTING
CABLE
LOAD
CABLE
TERMINATION
RECEIVER
1543 F19
50Ω
125Ω
50Ω
50Ω
125Ω
50Ω
Figure 20. V.35 Receiver Configuration
Figure 19. Typical V.35 Interface
R3
124Ω
R5
20k
LTC1344A
LTC1543
LTC1544
RECEIVER
1543 F18
A
B
A
'
B
'
C
'
R1
51.5Ω
R8
6k
S2
S3
R2
51.5Ω
R6
10k
R7
10k
GND
R4
20k
S1
R3
124Ω
R5
20k
LTC1344A
LTC1543
RECEIVER
1543 F20
A
B
A
'
B
'
C
'
R1
51.5Ω
R8
6k
S2
S3
R2
51.5Ω
R6
10k
R7
10k
GND
R4
20k
S1
