FEATURES
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LTC2870/LTC2871
RS232/RS485 Multiprotocol
Transceivers with
Integrated Termination
DESCRIPTION
The LTC
®
2870/LTC2871 are robust pin-configurable mul-
tiprotocol transceivers, supporting RS232, RS485, and
RS422 protocols, operating on a single 3V to 5.5V supply.
The LTC2870 can be configured as two RS232 single-ended
transceivers or one RS485 differential transceiver on shared
I/O lines. The LTC2871 offers independent control of two
RS232 transceivers and one RS485 transceiver, each on
dedicated I/O lines.
Pin-controlled integrated termination resistors allow
for easy interface reconfiguration, eliminating external
resistors and control relays. Half-duplex switches allow
four-wire and two-wire RS485 configurations. Loopback
mode steers the driver inputs to the receiver outputs for
diagnostic self-test.The RS485 receivers support up to
256 nodes per bus, and feature full failsafe operation for
floating, shorted or terminated inputs.
An integrated DC/DC boost converter uses a small induc-
tor and one capacitor, eliminating the need for multiple
supplies for driving RS232 levels.
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
One RS485 and Two RS232 Transceivers
3V to 5.5V Supply Voltage
20Mbps RS485 and 500kbps RS232
Automatic Selection of Integrated RS485 (120Ω)
and RS232 (5kΩ)Termination Resistors
Half-/Full-Duplex RS485 Switching
High ESD: ±26kV (LTC2870), ±16kV (LTC2871)
Logic Loopback Mode
1.7V to 5.5V Logic Interface
Supports Up to 256 RS485 Nodes
RS485 Receiver Failsafe Eliminates UART Lockup
Available in 28-Pin 4mm
×
5mm QFN and
TSSOP (LTC2870), and 38-Pin 5mm
×
7mm QFN
and TSSOP (LTC2871)
APPLICATIONS
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Flexible RS232/RS485/RS422 Interface
Software Selectable Multiprotocol Interface Ports
Point-of-Sale Terminals
Cable Repeaters
Protocol Translators
TYPICAL APPLICATIONS
Protocol Switching with
Automatic Termination Selection
1.7V TO V
CC
V
L
RS232 RS485
485/232
DY
Y
Z
A
DZ
RA
A
B
RB
RO
120Ω
B
DIN1
ROUT1
DIN2
ROUT2
DOUT1
RIN1
DOUT2
RIN2
RS485
FULL HALF
DUPLEX
RO,
RB
A
B
H/F
LTC2870
3V TO 5.5V
V
CC
RS485
TERMINATION
OFF ON
120Ω
DI
Z
DI,
DY
Y
Z
Simultaneous Protocols and
RS485 Termination Switching
1.7V TO V
CC
V
L
TE485
Y
LTC2871
3V TO 5.5V
V
CC
RS485 Duplex Switching
1.7V TO V
CC
V
L
LTC2870,
LTC2871
3V TO 5.5V
V
CC
28701 TA01
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LTC2870/LTC2871
ABSOLUTE MAXIMUM RATINGS
(Notes 1 and 2)
Input Supplies
V
CC
, V
L
..................................................... –0.3V to 7V
Generated Supplies
V
DD
................................................ V
CC
– 0.3V to 7.5V
V
EE
......................................................... 0.3V to –7.5V
V
DD
– V
EE
..............................................................15V
SW ........................................... –0.3V to (V
DD
+ 0.3V)
CAP............................................. 0.3V to (V
EE
– 0.3V)
A, B, Y, Z, RIN1, RIN2, DOUT1, DOUT2 ........–15V to 15V
DI, DZ, DY,
RXEN,
DXEN, LB, H/F, TE485,
RX485,
DX485,
RX232,
DX232, DIN1, DIN2,
485/232,
CH2.
.......................................... –0.3V to 7V
FEN, RA, RB, RO, ROUT1, ROUT2 ...–0.3V to (V
L
+ 0.3V)
Differential Enabled Terminator Voltage
(A-B or Y-Z) ..........................................................±6V
Operating Temperature
LTC2870C/LTC2871C ............................... 0°C to 70°C
LTC2870I/LTC2871I ............................. –40°C to 85°C
Storage Temperature Range .................. –65°C to 125°C
Lead Temperature (Soldering, 10 sec)
FE package........................................................ 300°C
PIN CONFIGURATION
LTC2870
TOP VIEW
TE485
GND
V
CC
H/F
LTC2870
TOP VIEW
LB
H/F
TE485
V
EE
RA
RB
485/232
RXEN
DXEN
1
2
3
4
5
6
7
8
9
29
V
EE
28 V
L
27 V
CC
26 GND
25 A
24 B
23 V
CC
22 Y
21 GND
20 Z
19 V
CC
18 V
DD
17 SW
16 GND
15 V
EE
LB
28 27 26 25 24 23
V
EE
1
RA 2
RB 3
485/232 4
RXEN
5
DXEN 6
DY 7
DZ 8
9 10 11 12 13 14
FEN
GND
CAP
V
EE
GND
SW
29
V
EE
22 A
21 B
20 V
CC
19 Y
18 GND
17 Z
16 V
CC
15 V
DD
V
L
DY 10
DZ 11
FEN 12
GND 13
CAP 14
UFD PACKAGE
28-LEAD (4mm 5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 43°C/W
EXPOSED PAD (PIN 29) IS V
EE
,
MUST BE SOLDERED TO PCB
FE PACKAGE
28-LEAD PLASTIC TSSOP
T
JMAX
= 125°C,
θ
JA
= 25°C/W
EXPOSED PAD (PIN 29) IS V
EE
,
MUST BE SOLDERED TO PCB
28701f
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LTC2870/LTC2871
PIN CONFIGURATIONS
LTC2871
TOP VIEW
TE485
GND
LTC2871
TOP VIEW
V
L
LB
V
CC
H/F
RO
LB
V
L
H/F
TE485
31 RIN1
30 RIN2
29 A
28 B
27 V
CC
39
V
EE
26 Y
25 GND
24 Z
23 DOUT1
22 DOUT2
21 V
CC
20 V
DD
13 14 15 16 17 18 19
V
EE
GND
SW
FEN
GND
CAP
V
EE
V
EE
ROUT1
ROUT2
CH2
RX485
1
2
3
4
5
6
7
8
9
39
V
EE
38 RO
27 V
CC
36 GND
35 RIN1
34 RIN2
33 A
32 B
31 V
CC
30 Y
29 GND
28 Z
27 DOUT1
26 DOUT2
25 V
CC
24 V
DD
23 V
EE
22 SW
21 GND
20 V
EE
38 37 36 35 34 33 32
V
EE
1
ROUT1 2
ROUT2 3
CH2
4
RX485
5
DX485 6
DI 7
DIN1 8
DIN2 9
DX232 10
RX232
11
V
EE
12
DX485 10
DI 11
DIN1 12
DIN2 13
DX232 14
RX232
15
V
EE
16
FEN 17
GND 18
CAP 19
UHF PACKAGE
38-LEAD (5mm 7mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 34°C/W
EXPOSED PAD (PIN 39) IS V
EE
,
MUST BE SOLDERED TO PCB
FE PACKAGE
38-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 29°C/W
EXPOSED PAD (PIN 39) IS V
EE
,
MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC2870CFE#PBF
LTC2870IFE#PBF
LTC2870CUFD#PBF
LTC2870IUFD#PBF
LTC2871CFE#PBF
LTC2871IFE#PBF
LTC2871CUHF#PBF
LTC2871IUHF#PBF
TAPE AND REEL
LTC2870CFE#TRPBF
LTC2870IFE#TRPBF
LTC2870CUFD#TRPBF
LTC2870IUFD#TRPBF
LTC2871CFE#TRPBF
LTC2871IFE#TRPBF
LTC2871CUHF#TRPBF
LTC2871IUHF#TRPBF
PART MARKING
LTC2870FE
LTC2870FE
2870
2870
LTC2871FE
LTC2871FE
2871
2871
PACKAGE DESCRIPTION
28-Lead Plastic TSSOP
28-Lead Plastic TSSOP
28-Lead (4mm
×
5mm) Plastic QFN
28-Lead (4mm
×
5mm) Plastic QFN
38-Lead Plastic TSSOP
38-Lead Plastic TSSOP
38-Lead (5mm
×
7mm) Plastic QFN
38-Lead (5mm
×
7mm) Plastic QFN
TEMPERATURE RANGE
0°C to 70°C
–40°C to 85°C
0°C to 70°C
–40°C to 85°C
0°C to 70°C
–40°C to 85°C
0°C to 70°C
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
PRODUCT SELECTION GUIDE
PART NUMBER
LTC2870
LTC2871
CONFIGURABLE TRANSCEIVER COMBINATIONS (RS485 + RS232)
(0 + 0), (1 + 0), (0 + 2)
(0 + 0), (1 + 0), (1 + 1), (1 + 2), (0 + 1), (0 + 2)
PACKAGES
28-Lead QFN, 28-Lead TSSOP
38-Lead QFN, 38-Lead TSSOP
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LTC2870/LTC2871
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER
Power Supply
V
CC
V
L
Supply Voltage Operating Range
Logic Supply Voltage Operating Range
V
CC
Supply Current in Shutdown Mode
V
L
≤ V
CC
RXEN
= V
L
, DXEN = TE485 = FEN = 0V, (LTC2870)
DX485 = DX232 = TE485 = FEN = H/F = 0V,
RX485
=
RX232
= V
L
(LTC2871)
485/232 = DXEN = V
L
,
RXEN
= 0V,
DY/DZ = 0V or V
L
(LTC2870)
DX485 = DX232 = V
L
,
RX485
=
RX232
= 0V,
DI/DIN1/DIN2 = 0V or V
L
(LTC2871)
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= V
L
= 3.3V, TE485 = 0V, LB = 0V unless otherwise noted.
CONDITIONS
MIN
3
1.7
8
TYP
MAX
5.5
V
CC
60
UNITS
V
V
μA
V
CC
Supply Current in Transceiver Mode
(Outputs Unloaded) (Note 3)
V
L
Supply Current in Transceiver Mode
(Outputs Unloaded)
RS485 Driver
|V
OD
|
Differential Output Voltage
3.3
l
mA
5
μA
0
R
L
= ∞, V
CC
= 3V (Figure 1)
R
L
= 27Ω, V
CC
= 3V (Figure 1)
R
L
= 50Ω, V
CC
= 3.13V (Figure 1)
R
L
= 27Ω, V
CC
= 3V (Figure 1)
R
L
= 50Ω, V
CC
= 3.13V (Figure 1)
R
L
= 27Ω or 50Ω (Figure 1)
R
L
= 27Ω or 50Ω (Figure 1)
l
l
l
l
l
l
l
1.5
1.5
2
6
V
CC
V
CC
0.2
0.2
3
0.2
V
V
V
V
V
V
V
Δ|V
OD
|
V
OC
Δ|V
OC
|
Difference in Magnitude of Differential Output
Voltage for Complementary Output States
Common Mode Output Voltage
Difference in Magnitude of Common Mode
Output Voltage for Complementary Output
States
Three-State (High Impedance) Output Current
Maximum Short-Circuit Current
Input Current
Input Resistance
Differential Input Signal Threshold Voltage
(A-B)
Input Hysteresis
Differential Input Failsafe Threshold Voltage
Input DC Failsafe Hysteresis
I
OZD485
I
OSD485
I
IN485
R
IN485
V
OUT
= 12V or –7V, V
CC
= 0V or 3.3V (Figure 2)
–7V ≤ V
OUT
≤ 12V (Figure 2)
V
IN
= 12V or –7V, V
CC
= 0V or 3.3V (Figure 3)
(Note 5)
V
IN
= 12V or –7V, V
CC
= 0V or 3.3V (Figure 3)
(Note 5)
–7V ≤ (A or B) ≤ 12V (Note 5)
B = 0V (Notes 3, 5)
–7V ≤ (A or B) ≤ 12V (Note 5)
B = 0V (Note 5)
Output Low, I(RA, RO) = 3mA (Sinking),
3V ≤ V
L
≤ 5.5V
Output Low, I(RA, RO) = 1mA (Sinking),
1.7V ≤ V
L
< 3V
l
l
–100
–250
–100
96
125
125
250
125
μA
mA
μA
kΩ
RS485 Receiver
l
l
l
±200
130
mV
mV
l
–200
–50
25
0
0.4
0.4
mV
mV
V
V
V
V
V
OL
Output Low Voltage
l
l
l
l
l
l
V
OH
Output High Voltage
Output High, I(RA, RO) = –3mA (Sourcing),
3V ≤ V
L
≤ 5.5V
Output High, I(RA, RO) = –1mA (Sourcing),
1.7V ≤ V
L
< 3V
V
L
– 0.4
V
L
– 0.4
0
±5
±125
Three-State (High Impedance) Output Current
Short-Circuit Output Current
0V ≤ (RA, RO), ≤V
L
, V
L
= 5.5V
0V ≤ (RA, RO), ≤V
L
, V
L
= 5.5V
μA
mA
28701f
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LTC2870/LTC2871
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER
R
TERM
Terminating Resistor
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= V
L
= 3.3V, TE485 = 0V, LB = 0V unless otherwise noted.
CONDITIONS
TE485 = V
L
, A – B = 2V, B = –7V, 0V, 10V
(Figure 8) (Note 5)
R
L
= 3kΩ; V
EE
≤ –5.9V
R
L
= 3kΩ; V
DD
≥ 6.5V
Y or Z (LTC2870) = ±15V
RS232 Receiver Enabled
DOUT1 or DOUT2 (LTC2871) = ±15V
Driver Output = 0V
l
MIN
108
TYP
120
MAX
156
UNITS
Ω
RS232 Driver
V
OLD
V
OHD
Output Low Voltage
Output High Voltage
Three-State (High Impedance) Output Current
l
l
l
l
l
l
l
–5
5
–5.7
6.2
–7.5
7.5
±156
±10
V
V
μA
μA
mA
V
V
V
V
Output Short-Circuit Current
RS232 Receiver
Input Threshold Voltage
Input Hysteresis
Output Low Voltage
Output High Voltage
Input Resistance
Three-State (High Impedance) Output Current
Output Short-Circuit Current
Logic Inputs
Threshold Voltage
Input Current
Power Supply Generator
V
DD
V
EE
ESD
LTC2870 Interface Pins (A, B, Y, Z)
LTC2871 Interface Pins (A, B, Y, Z, RIN1, RIN2,
DOUT1, DOUT2)
All Other Pins
Regulated V
DD
Output Voltage
Regulated V
EE
Output Voltage
±35
0.6
0.1
1.5
0.4
±90
2.5
1.0
0.4
I(RA, RB, ROUT1, ROUT2) = 1mA (Sinking)
1.7V ≤ V
L
≤ 5.5V
I(RA, RB, ROUT1, ROUT2) = –1mA (Sourcing)
1.7V ≤ V
L
≤ 5.5V
–15V ≤ (A, B, RIN1, RIN2) ≤ 15V,
RS232 Receiver Enabled
0V ≤ (RA, RB, ROUT1, ROUT2) ≤ V
L
V
L
= 5.5V
0V ≤ (RA, RB, ROUT1, ROUT2) ≤ V
L
l
l
l
l
l
V
L
– 0.4
3
5
0
±25
7
±5
±50
kΩ
μA
mA
l
l
0.4
0
7
–6.3
0.75 • V
L
±5
V
μA
V
V
RS232 Drivers Enabled, Outputs Loaded with
R
L
= 3kΩ to GND, DIN1/DY = V
L
, DIN2/DZ = 0V
(Note 3)
Human Body Model to GND or V
CC
, Powered or
Unpowered (Note 7)
Human Body Model (Note 7)
±26
±16
±4
kV
kV
kV
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