LTC2846 Linear Technology, LTC2846 Datasheet - Page 13

• Manufacturer Part Number: LTC2846
• Description: 3.3V Software-Selectable Multiprotocol Transceiver with Termination
• Manufacturer: Linear Technology

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APPLICATIO S I FOR ATIO
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
4
U
LTC2846
LTC2844
DCE/DTE
DCE/DTE
U
(DATA)
(DATA)
M0
M1
M2
M2
M1
M0
15
16
18
19
14
13
12
11
Figure 18. Single Port DCE V.35 Mode Selection in the Cable
W
U
CONNECTOR
–3.25mA
GENERATOR
–10V
Figure 20. V.10 Receiver Input Impedance
NC
NC
Figure 19. Typical V.10 Interface
C
A
INTERCONNECTING
BALANCED
2846 F18
–3V
CABLE
I
Z
C
A
TERMINATION
CABLE
'
'
3V
CABLE
LTC2846
LOAD
RECEIVER
sn2846 2846fs
10V
13
2846 F19
3.25mA
V
Z
2846 F20