LTC1343 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC1343' PDF : 28 Pages View PDF
LTC1343
APPLICATIONS INFORMATION
A'
A
R1
LTC1344
51.5Ω
R8
R5
20k
6k
S1
S3
R3
S2 124Ω
LTC1343
R6
10k
RECEIVER
R2
51.5Ω
B'
R7
R4
10k
B
20k
S4
C'
GND
1343 F19
Figure 19. V.28 Receiver Configuration
A'
A
R1
LTC1344
51.5Ω
R8
6k
R5
20k
S1
R3
S3
S2 124Ω
R2
51.5Ω
B'
C'
R4
B
20k
S4
GND
LTC1343
R6
10k
RECEIVER
R7
10k
1343 F21
Figure 21. V.35 Receiver Configuration
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
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 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.
GENERATOR
BALANCED
INTERCONNECTING
CABLE
LOAD
CABLE
TERMINATION
RECEIVER
A
A'
50Ω
125Ω
50Ω
125Ω
50Ω
B
C
50Ω
B'
C'
1343 F20
Figure 20. Typical V.35 Interface
The generator differential impedance must be 50Ω to
150Ω and the impedance between shorted terminals (A
and B) and ground C must be 150Ω ±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.
A
LTC1344
V.35 DRIVER
124Ω
51.5Ω
S1
S2
ON
ON
C1
100pF
51.5Ω
B
C
1343 F22
Figure 22. V.35 Driver Using the LTC1344
13
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