ltc2844 Linear Technology Corporation, ltc2844 Datasheet - Page 13

• Manufacturer Part Number: ltc2844
• Description: 3.3v Software-selectable Multiprotocol Transceiver
• Manufacturer: Linear Technology Corporation

APPLICATIONS
V.11 (RS422) Interface
A typical V.11 balanced interface is shown in Figure 14. A
V.11 differential generator with outputs A and B with
ground C is connected to a differential receiver with
ground C
V.11 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 required
to prevent reflections from corrupting the data. The
receiver inputs must also be compliant with the imped-
ance curve shown in Figure 12.
In V.11 mode, all switches are off except S1 of the
LTC2846’s receivers which connects a 103 differential
termination impedance to the cable as shown in Figure
15
termination other than its V.11 receivers’ 30k input imped-
ance is necessary.
1
. The LTC2844 only handles control signals, so no
GENERATOR
GENERATOR
'
, inputs A
Figure 14. Typical V.11 Interface
Figure 16. Typical V.28 Interface
A
B
C
C
A
INTERCONNECTING
INTERCONNECTING
'
U
connected to A, B
BALANCED
BALANCED
CABLE
CABLE
INFORMATION
U
A
B
C
C
A
TERMINATION
TERMINATION
'
'
'
'
'
W
CABLE
CABLE
'
connected to B. The
100
MIN
LOAD
LOAD
RECEIVER
U
RECEIVER
2844 F16
2844 F14
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
nected to A, ground C
ground C.
In V.28 mode all switches are off except S3 inside the
LTC2846/LTC2844 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/
LTC2844 receiver and connected to a TTL level reference
voltage for a 1.4V receiver trip point.
1
networks on the LTC2846 can be treated identically if it is assumed that an S1 switch exists and is
always closed on the R2 and R3 receivers.
Actually, there is no switch S1 in receivers R2 and R3. However, for simplicity, all termination
A
B
C
'
'
'
Figure 15. V.11 Receiver Configuration
Figure 17. V.28 Receiver Configuration
R1
51.5
S1
R2
51.5
C
A
B
'
'
'
S2
124
R3
GND
R8
6k
S3
'
20k
20k
R5
R4
connected via the signal return
GND
R8
6k
S3
20k
20k
R5
R4
R6
10k
R7
10k
R6
10k
R7
10k
RECEIVER
LTC2844
2844 F17
LTC2844
RECEIVER
LTC2846
2844 F15
sn2844 2844fs
13
'
con-