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LTC2844IG#TRPBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P20
13
LTC2844
sn2844 2844fs
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', inputs A' connected to A, B' connected to B. The
V.11 interface has a differential termination at the receiver
end that has a minimum value of 100Ω. 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 103Ω differential
termination impedance to the cable as shown in Figure
15
1
. The LTC2844 only handles control signals, so no
termination other than its V.11 receivers’ 30k input imped-
ance is necessary.
Figure 15. V.11 Receiver Configuration
AA'
B
C
B'
C'
GENERATOR
BALANCED
INTERCONNECTING
CABLE
LOAD
CABLE
TERMINATION
RECEIVER
100Ω
MIN
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' con-
nected to A, ground C' connected via the signal return
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.
AA
'
CC
'
GENERATOR
BALANCED
INTERCONNECTING
CABLE
LOAD
CABLE
TERMINATION
RECEIVER
2844 F16
Figure 14. Typical V.11 Interface
R5
20k
LTC2844
RECEIVER
2844 F17
A'
B'
C'
R8
6k
S3
R6
10k
R7
10k
GND
R4
20k
Figure 17. V.28 Receiver Configuration
Figure 16. Typical V.28 Interface
APPLICATIONS INFORMATION
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1
Actually, there is no switch S1 in receivers R2 and R3. However, for simplicity, all termination
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.
R3
124Ω
R5
20k
LTC2846
RECEIVER
2844 F15
A
'
B
'
C
'
R1
51.5Ω
R8
6k
S2
S3
R2
51.5Ω
R6
10k
R7
10k
GND
R4
20k
S1
14
LTC2844
sn2844 2844fs
A
A
'
B
C
B
'
C
'
GENERATOR
BALANCED
INTERCONNECTING
CABLE
LOAD
CABLE
TERMINATION
RECEIVER
2844 F18
50Ω
125Ω
50Ω
50Ω
125Ω
50Ω
Figure 18. Typical V.35 Interface
Figure 19. V.35 Receiver Configuration
V.35 Interface
A typical V.35 balanced interface is shown in Figure 18. A
V.35 differential generator with outputs A and B with
ground C is connected to a differential receiver with
ground C', inputs A' connected to A, B' connected to B. The
V.35 interface requires a T or delta network termination at
the receiver end and the generator end. The receiver
differential impedance measured at the connector must be
100Ω␣ ±10Ω, and the impedance between shorted termi-
nals (A' and B') and ground C' must be 150Ω ±15Ω.
In V.35 mode, both switches S1 and S2 inside the LTC2846
are on, connecting the T network impedance as shown in
Figure 19. The 30k input impedance of the receiver is
placed in parallel with the T network termination, but does
not affect the overall input impedance significantly.
The generator differential impedance must be 50Ω to
150Ω and the impedance between shorted terminals (A
and B) and ground C must be 150Ω ±15Ω. For the
generator termination, switches S1 and S2 are both on as
shown in Figure 20.
No-Cable Mode
The no-cable mode (M0 = M1 = M2 = 1) is intended for the
case when the cable is disconnected from the connector.
The bias circuitry, drivers and receivers are turned off, the
driver outputs are forced into a high impedance state, and
the supply current drops to less than 600µA.
LTC2846 Supplies
The LTC2846 uses an internal capacitive charge pump to
generate V
DD
and V
EE
as shown in Figure 21. A voltage
doubler generates about 8V on V
DD
and a voltage inverter
generates about – 7.5V for V
EE
. Three 1µF surface mounted
tantalum or ceramic capacitors are required for C1, C2 and
C3. The V
EE
capacitor C4 should be a minimum of 3.3µF.
All capacitors are 16V and should be placed as close as
possible to the LTC2846 to reduce EMI.
The LTC2846 has an internal boost switching regulator
which generates a 5V output from the 3.3V supply as
shown in Figure 22. The 5V V
CC
supplies its internal charge
pump and transceivers as well as its companion chip.
APPLICATIONS INFORMATION
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Figure 20. V.35 Driver
V.35 DRIVER
A
B
C
51.5Ω
S2
S1
2844 F20
51.5Ω
LTC2846
124Ω
R3
124Ω
R5
20k
LTC2846
RECEIVER
2844 F19
A
'
B
'
C
'
R1
51.5Ω
R8
6k
S2
S3
R2
51.5Ω
R6
10k
R7
10k
GND
R4
20k
S1
33
32
31
30
2844 F21
7
6
5
8
C3
1µF
C5
10µF
5V
C1
1µF
C2
1µF
C4
3.3µF
LTC2846
V
DD
C1
+
C1
–
V
CC
C2
+
C2
–
V
EE
GND
+
Figure 21. Charge Pump
15
LTC2844
sn2844 2844fs
mode, the TXD signal is routed to Pins 2 and 14 via Driver␣ 1
in the LTC2846. In DCE mode, Driver 1 now routes the RXD
signal to Pins 2 and 14.
Multiprotocol Interface with RL, LL, TM and a DB-25
Connector
If the RL, LL and TM signals are implemented, there are not
enough drivers and receivers available in the LTC2846/
LTC2844. In Figure 25, the required control signals are
handled by the LTC2845. The LTC2845 has an additional
single-ended driver/receiver pair that can handle two more
optional control signals such as TM and LL.
Cable-Selectable Multiprotocol Interface
A cable-selectable multiprotocol DTE/DCE interface is
shown in Figure 26. The select lines M0, M1 and DCE/DTE
are brought out to the connector. The mode is selected by
the cable by wiring M0 (connector Pin 18) and M1 (con-
nector Pin 21) and DCE/DTE (connector Pin 25) to ground
(connector Pin 7) or letting them float. If M0, M1 or DCE/
DTE is floating, internal pull-up current sources will pull
the signals to V
IN
. The select bit M2 is floating and
therefore, internally pulled high. When the cable is pulled
out, the interface will go into the no-cable mode.
Compliance Testing
The LTC2846/LTC2844 chipset has been tested by TUV
Rheinland of North America Inc. and passed the NET1,
NET2 and TBR2 requirements. Copies of the test report are
available from LTC or TUV Rheinland of North America Inc.
The title of the report is Test Report No. TBR2/051501/02
The address of TUV Rheinland of North America Inc. is:
Receiver Fail-Safe
All LTC2846/LTC2844 receivers feature fail-safe opera-
tion in all modes. If the receiver inputs are left floating or
shorted together by a termination resistor, the receiver
output will always be forced to a logic high.
DTE vs DCE Operation
The DCE/DTE pin acts as an enable for Driver 3/Receiver␣ 1
in the LTC2846, and Driver 3/Receiver 1 and Receiver 4/
Driver 4 in the LTC2844.
The LTC2846/LTC2844 can be configured for either DTE
or DCE operation in one of two ways: a dedicated DTE or
DCE port with a connector of appropriate gender or a port
with one connector that can be configured for DTE or DCE
operation by rerouting the signals to the LTC2846/LTC2844
using a dedicated DTE cable or dedicated DCE cable.
A dedicated DTE port using a DB-25 male connector is
shown in Figure 23. The interface mode is selected by logic
outputs from the controller or from jumpers to either V
IN
or GND on the mode select pins.
A port with one DB-25 connector, but can be configured
for either DTE or DCE operation is shown in Figure 24. The
configuration requires separate cables for proper signal
routing in DTE or DCE operation. For example, in DTE
APPLICATIONS INFORMATION
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Figure 22. Boost Switching Regulator
GND
V
IN
SW
SHDN FB
V
IN
3.3V
4
35
2844 F22
D1
L1
5.6µH
2, 34
R1
13k
BOOST
SWITCHING
REGULATOR
C5
10µF
C6
10µF
R2
4.3k
V
CC
5V
480mA
C1,C2: TAIYO YUDEN X5R JMK316BJ106ML
D1: ON SEMICONDUCTOR MBR0520
L1: SUMIDA CR43-5R6
SHDN
336
TUV Rheinland of North America Inc.
1775, Old Highway 8 NW, Suite 107
St. Paul, MN 55112
Tel. (651) 639-0775
Fax (651) 639-0873
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P20

LTC2844IG#TRPBF

Mfr. #:
Buy LTC2844IG#TRPBF
Manufacturer:
Analog Devices Inc.
Description:
RS-232 Interface IC 3.3V Sftwr-Sel Multiprotocol Tran
Lifecycle:
New from this manufacturer.
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