LTC1343 Linear Technology, LTC1343 Datasheet - Page 13

• Manufacturer Part Number: LTC1343
• Description: Software-Selectable Multiprotocol Transceiver
• Manufacturer: Linear Technology

APPLICATIONS
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
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
nals (A
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.
B
C
A
'
'
'
GENERATOR
50
50
'
10 , and the impedance between shorted termi-
R1
51.5
R2
51.5
and B) and ground C
S1
'
, inputs A
S2
Figure 19. V.28 Receiver Configuration
125
Figure 20. Typical V.35 Interface
124
LTC1344
R3
A
B
C
'
U
INTERCONNECTING
connected to A, B
BALANCED
CABLE
A
B
INFORMATION
U
GND
R8
6k
'
S3
must be 150
20k
20k
R4
S4
R5
C
B
A
'
'
'
W
TERMINATION
'
connected to B. The
125
CABLE
R6
10k
R7
10k
LOAD
50
50
RECEIVER
U
LTC1343
15 .
RECEIVER
1343 F19
1343 F20
The generator differential impedance must be 50
150 and the impedance between shorted terminals (A
and B) and ground C must be 150
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.
B
C
A
'
'
'
R1
51.5
R2
51.5
S1
V.35 DRIVER
S2
Figure 22. V.35 Driver Using the LTC1344
Figure 21. V.35 Receiver Configuration
124
LTC1344
R3
LTC1344
A
B
124
GND
R8
6k
S3
C1
100pF
20k
20k
S4
R5
R4
ON
S2
S1
ON
51.5
51.5
R6
10k
R7
10k
LTC1343
15 . For the
RECEIVER
LTC1343
1343 F22
A
B
C
13
1343 F21
to