LTC2844CG#PBF Linear Technology, LTC2844CG#PBF Datasheet - Page 12

• Manufacturer Part Number: LTC2844CG#PBF
• Description: IC TXRX 3.3V MULTIPROTCOL 28SSOP
• Manufacturer: Linear Technology
• Type: Transceiverr

Specifications of LTC2844CG#PBF

• Number Of Drivers/receivers: 4/4
• Protocol: Multiprotocol
• Voltage - Supply: 3.3V
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIONS
LTC2844
Cable Termination
Traditional implementations have included switching
resistors with expensive relays, or required 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 or separate termina-
tions are built on the board and a custom cable routes the
signals to the appropriate termination. Switching the
termination with 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.
Using the LTC2846/LTC2844 solves the cable termination
switching problem. Via software control, appropriate ter-
mination for the V.10 (RS423), V.11 (RS422), V.28 (RS232)
and V.35 electrical protocols is chosen.
V.10 (RS423) Interface
A typical V.10 unbalanced interface is shown in Figure 11.
A V.10 single-ended generator output A with ground C is
connected to a differential receiver with inputs 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 12.
12
GENERATOR
Figure 11. Typical V.10 Interface
C
A
INTERCONNECTING
U
BALANCED
CABLE
'
INFORMATION
U
connected to the signal return
C
A
TERMINATION
'
'
W
CABLE
LOAD
RECEIVER
U
2844 F11
'
con-
–3.25mA
The V.10 receiver configuration in the LTC2844 is shown
in Figure 13. In V.10 mode switch S3 inside the LTC2844
is turned off.The noninverting input is disconnected inside
the LTC2844 receiver and connected to ground. The cable
termination is then the 30k input impedance to ground of
the LTC2844 V.10 receiver.
–10V
Figure 12. V.10 Receiver Input Impedance
Figure 13. V.10 Receiver Configuration
C
B
A
'
'
'
GND
R8
6k
S3
–3V
20k
20k
R5
R4
I
Z
R6
10k
R7
10k
3V
RECEIVER
LTC2844
2844 F13
sn2844 2844fs
10V
2844 F12
V
3.25mA
Z