LTC1546 Linear Technology, LTC1546 Datasheet - Page 12

• Manufacturer Part Number: LTC1546
• Description: Software-Selectable Multiprotocol Transceiver with Termination
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
LTC1546
interface has a differential termination at the receiver end
that has a minimum value of 100 . The termination
resistor is optional in the V.11 specification, but for the
high speed clock and data lines, the termination is essen-
tial to prevent reflections from corrupting the data. The
receiver inputs must also be compliant with the imped-
ance curve shown in Figure 20.
In V.11 mode, all switches are off except S1 of the
LTC1546’s receivers which connects a 103 differential
termination impedance to the cable as shown in Figure
23
termination other than its V.11 receivers’ 30k input imped-
ance is necessary.
V.28 (RS232) Interface
A typical V.28 unbalanced interface is shown in Figure 24.
A V.28 single-ended generator with output A and ground
C is connected to a single-ended receiver with input A
1
networks on the LTC1546 can be treated identically if it is assumed that an S1 switch exists and is
always closed on the R2 and R3 receivers.
12
Actually, there is no switch S1 in receivers R2 and R3. However, for simplicity, all termination
1
. The LTC1544 only handles control signals, so no
GENERATOR
B
C
A
'
'
'
Figure 21. V.10 Receiver Configuration
A
B
Figure 22. Typical V.11 Interface
C
A
B
INTERCONNECTING
U
BALANCED
GND
CABLE
R8
6k
S3
20k
20k
U
R5
R4
A
B
C
TERMINATION
R6
10k
R7
10k
'
'
'
W
CABLE
RECEIVER
LTC1544
100
MIN
LOAD
1546 F21
RECEIVER
U
1546 F22
'
connected to A and ground C
return to ground C.
In V.28 mode, S3 is closed inside the LTC1546/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 25. Proper termination is only pro-
vided when the B input of the receivers is floating, since S1
of the LTC1546’s R2 and R3 receivers remains on in V.28
mode
LTC1546/LTC1544 receiver and connected to a TTL level
reference voltage to give a 1.4V receiver trip point.
GENERATOR
1
. The noninverting input is disconnected inside the
B
C
A
C
A
B
'
'
'
'
'
'
Figure 23. V.11 Receiver Configuration
Figure 25. V.28 Receiver Configuration
R1
51.5
S1
R2
51.5
S1
R1
51.5
R2
51.5
Figure 24. Typical V.28 Interface
S2
S2
C
A
INTERCONNECTING
124
124
R3
R3
BALANCED
CABLE
GND
GND
R8
6k
R8
6k
S3
S3
20k
20k
R5
R4
20k
20k
R5
R4
'
connected via the signal
C
A
TERMINATION
'
'
CABLE
R6
10k
R7
10k
R6
10k
R7
10k
RECEIVER
LOAD
RECEIVER
LTC1546
LTC1546
1546 F23
1546 F25
RECEIVER
1546 F24