Datasheet
13
LTC2846
sn2846 2846fs
Figure 18. Single Port DCE V.35 Mode Selection in the Cable
Figure 20. V.10 Receiver Input Impedance
Figure 19. Typical V.10 Interface
APPLICATIO S I FOR ATIO
WUUU
selected. Switching the terminations with FETs is difficult
because the FETs must remain off when the signal voltage
is beyond the supply voltage. Alternatively, custom cables
may contain termination in the cable head or route signals
to various terminations on the board.
The LTC2846/LTC2844 chip set solves the cable termina-
tion switching problem by automatically providing the
appropriate termination and switching on-chip for the
V.10 (RS423), V.11 (RS422), V.28 (RS232) and V.35
electrical protocols.
V.10 (RS423) Interface
All V.10 drivers and receivers necessary for the RS449,
EIA530, EIA530-A, V.36 and X.21 protocols are imple-
mented on the LTC2844 or LTC2845.
A typical V.10 unbalanced interface is shown in Figure 19.
A V.10 single-ended generator with output A and ground
C is connected to a differential receiver with input A' con-
nected to A, and ground C' connected via the signal return
to ground C. Usually, no cable termination is required for
V.10 interfaces, but the receiver inputs must be compliant
with the impedance curve shown in Figure 20.
The V.10 receiver configuration in the LTC2844 and
LTC2845 is shown in Figure 21. In V.10 mode, switch S3
inside the LTC2844 and LTC2845 is turned off. The
noninverting input is disconnected inside the LTC2844
NC
NC
CABLE
2846 F18
15
16
18
19
LTC2846
LTC2844
CONNECTOR
14
13
12
11
(DATA)
M0
M1
M2
DCE/DTE
DCE/DTE
M2
M1
M0
(DATA)
AA
'
CC
'
GENERATOR
BALANCED
INTERCONNECTING
CABLE
LOAD
CABLE
TERMINATION
RECEIVER
2846 F19
I
Z
V
Z
–10V
–3.25mA
3.25mA
–3V
3V 10V
2846 F20