LTC1344AIG#TRPBF Linear Technology, LTC1344AIG#TRPBF Datasheet - Page 6

• Manufacturer Part Number: LTC1344AIG#TRPBF
• Description: IC CABLE TERM MULTIPROTCL 24SSOP
• Manufacturer: Linear Technology
• Type: Cabler

Specifications of LTC1344AIG#TRPBF

• Number Of Terminations: 6
• Voltage - Supply: 4.75 V ~ 5.25 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-SSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIONS
LTC1344A
Multiprotocol Cable Termination
One of the most difficult problems facing the designer of
a multiprotocol serial interface is how to allow the trans-
mitters and receivers for different electrical standards to
share connector pins. In some cases the transmitters and
receivers for each interface standard can be simply tied
together and the appropriate circuitry enabled. But the
biggest problem still remains: how to switch the various
cable termination required by the different standards.
Traditional implementations have included switching re-
sistors with expensive relays or requiring the user to
change termination modules every time the interface
standard has changed. Custom cables have been used
with the termination in the cable head. Another method
uses separate termination built on the board, and a custom
cable which routes the signals to the appropriate termina-
tion. Switching the termination using FETs is difficult
because the FETs must remain off even though the signal
voltage is beyond the supply voltage for the FET drivers or
the power is off.
The LTC1344A solves the cable termination switching
problem via software control. The LTC1344A provides
termination for the V.10 (RS423), V.11 (RS422), V.28
(RS232) and V.35 electrical protocols.
V.10 (RS423) Termination
A typical V.10 unbalanced interface is shown in Figure 4.
A V.10 single-ended generator output A with ground C is
connected to a differential receiver with input A
nected to A and input C
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 5.
In V.10 mode, both switches S1 and S2 are turned off so
the only cable termination is the input impedance of the
V.10 receiver.
6
U
'
INFORMATION
connected to the signal return
U
W
U
'
con-
V.11 (RS422) Termination
A typical V.11 balanced interface is shown in Figure 6. 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 requires a differential termination at the
receiver end that has a minimum value of 100 . The
receiver inputs must also be compliant with the imped-
ance curve shown in Figure 7.
In V.11 mode, switch S1 is turned on and S2 is turned off
so the cable is terminated with a 103 impedance.
Z
GENERATOR
Figure 5. V.10 Interface Using the LTC1344A
'
, inputs A
A
B
C
OFF
– 3.25mA
S1
Figure 4. Typical V.10 Interface
51.5
51.5
–10V
INTERCONNECTING
'
A
C
OFF
S2
connected to A, B
BALANCED
CABLE
LTC1344A
124
–3V
I
Z
A
C
TERMINATION
'
'
3V
CABLE
'
Z
Z
connected to B. The
LOAD
RECEIVER
V.10
10V
RECEIVER
3.25mA
V
Z
1344 F05
1344 F04