LTC2871CUHFPBF
更新时间：2024-09-18 12:01:23
品牌：Linear
描述：RS232/RS485 Multiprotocol Transceivers with Integrated Termination
概述
数据手册LTC2871CUHFPBF 概述
RS232/RS485 Multiprotocol Transceivers with Integrated Termination RS232 / RS485多协议收发器，集成终端
LTC2871CUHFPBF 数据手册
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PDF下载LTC2870/LTC2871
RS232/RS485 Multiprotocol
Transceivers with
Integrated Termination
DESCRIPTION
FEATURES
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.
TheLTC2870canbeconfiguredastwoRS232single-ended
transceiversoroneRS485differentialtransceiveronshared
I/O lines. The LTC2871 offers independent control of two
RS232 transceivers and one RS485 transceiver, each on
dedicated I/O lines.
n
One RS485 and Two RS232 Transceivers
n
3V to 5.5V Supply Voltage
n
20Mbps RS485 and 500kbps RS232
n
Automatic Selection of Integrated RS485 (120Ω)
and RS232 (5kΩ)Termination Resistors
n
Half-/Full-Duplex RS485 Switching
n
High ESD: 2ꢀkV (ꢁTC2870), 1ꢀkV (ꢁTC2871)
n
Logic Loopback Mode
1.7V to 5.5V Logic Interface
Supports Up to 256 RS485 Nodes
n
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.
n
n
RS485 Receiver Failsafe Eliminates UART Lockup
n
Available in 28-Pin 4mm × 5mm QFN and
TSSOP (LTC2870), and 38-Pin 5mm × 7mm QFN
and TSSOP (LTC2871)
APPLICATIONS
n
Flexible RS232/RS485/RS422 Interface
An integrated DC/DC boost converter uses a small induc-
tor and one capacitor, eliminating the need for multiple
supplies for driving RS232 levels.
n
Software Selectable Multiprotocol Interface Ports
n
Point-of-Sale Terminals
n
Cable Repeaters
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.
n
Protocol Translators
TYPICAL APPLICATIONS
Protocol Switching with
Simultaneous Protocols and
RS485 Termination Switching
RS485 Duplex Switching
Automatic Termination Selection
1.7V TO V
1.7V TO V
1.7V TO V
3V TO 5.5V
3V TO 5.5V
3V TO 5.5V
CC
CC
CC
LTC2870
LTC2871
LTC2870,
LTC2871
V
V
V
V
V
V
CC
L
CC
L
CC
L
485/232
TE485
RS485
RS232 RS485
TERMINATION
OFF ON
Y
DY
120Ω
120Ω
Y
Z
Y
Z
DI
DI,
DY
Z
A
DZ
RA
RO
RS485
FULL HALF
DUPLEX
B
H/F
DIN1
DOUT1
RIN1
A
B
A
B
ROUT1
DIN2
RO,
RB
DOUT2
RIN2
RB
ROUT2
28701 TA01
28701f
1
LTC2870/LTC2871
(Notes 1 and 2)
ABSOLUTE MAXIMUM RATINGS
Input Supplies
FEN, RA, RB, RO, ROUT1, ROUT2...–0.3V to (V + 0.3V)
L
Differential Enabled Terminator Voltage
V , V ..................................................... –0.3V to 7V
CC
L
Generated Supplies
................................................V – 0.3V to 7.5V
(A-B or Y-Z) .......................................................... 6V
Operating Temperature
V
DD
CC
V .........................................................0.3V to –7.5V
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)
EE
DD
V
– V ..............................................................15V
EE
SW........................................... –0.3V to (V + 0.3V)
CAP............................................. 0.3V to (V – 0.3V)
DD
EE
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,
FE package........................................................300°C
485/232, CH2........................................... –0.3V to 7V
PIN CONFIGURATION
LTC2870
LTC2870
TOP VIEW
TOP VIEW
1
2
V
V
28
27
26
25
24
23
22
21
20
19
18
17
16
15
LB
H/F
L
CC
3
GND
A
TE485
28 27 26 25 24 23
4
V
EE
V
1
2
3
4
5
6
7
8
22
21
20
19
18
17
16
15
A
B
V
Y
EE
5
B
RA
RB
RA
RB
6
V
CC
CC
7
Y
485/232
RXEN
DXEN
DY
485/232
RXEN
DXEN
DY
29
29
EE
V
8
GND
Z
EE
V
GND
Z
9
10
11
12
13
14
V
V
V
CC
CC
DD
V
DZ
DZ
DD
9
10 11 12 13 14
UFD PACKAGE
SW
FEN
GND
GND
CAP
V
EE
28-LEAD (4mm s 5mm) PLASTIC QFN
FE PACKAGE
28-LEAD PLASTIC TSSOP
T
= 125°C, θ = 43°C/W
JMAX
JA
EXPOSED PAD (PIN 29) IS V
,
EE
T
= 125°C, θ = 25°C/W
JA
JMAX
MUST BE SOLDERED TO PCB
EXPOSED PAD (PIN 29) IS V
MUST BE SOLDERED TO PCB
,
EE
28701f
2
LTC2870/LTC2871
PIN CONFIGURATIONS
LTC2871
LTC2871
TOP VIEW
TOP VIEW
1
2
RO
V
38
27
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
20
V
L
LB
H/F
CC
3
GND
RIN1
RIN2
A
38 37 36 35 34 33 32
4
TE485
V
1
2
3
4
5
6
7
8
9
31 RIN1
30 RIN2
5
EE
V
EE
ROUT1
ROUT2
CH2
6
ROUT1
ROUT2
CH2
A
B
V
Y
29
28
27
26
7
B
8
V
CC
RX485
DX485
DI
CC
9
Y
RX485
DX485
DI
10
11
12
13
14
15
16
17
18
19
GND
Z
39
EE
39
25 GND
24
V
V
EE
DIN1
DIN2
Z
DOUT1
DOUT2
DIN1
23 DOUT1
22 DOUT2
DIN2
DX232 10
V
DX232
RX232
CC
RX232 11
21
20
V
V
CC
DD
V
V
EE
12
DD
V
V
EE
13 14 15 16 17 18 19
UHF PACKAGE
EE
SW
FEN
GND
CAP
GND
V
EE
38-LEAD (5mm s 7mm) PLASTIC QFN
FE PACKAGE
T
= 125°C, θ = 34°C/W
JMAX
JA
38-LEAD PLASTIC SSOP
EXPOSED PAD (PIN 39) IS V
,
EE
T
JMAX
= 125°C, θ = 29°C/W
JA
MUST BE SOLDERED TO PCB
EXPOSED PAD (PIN 39) IS V
,
EE
MUST BE SOLDERED TO PCB
ORDER INFORMATION
ꢁEAD FREE FINISH
TAPE AND REEꢁ
PART MARKING
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC2870CFE#PBF
LTC2870IFE#PBF
LTC2870CFE#TRPBF
LTC2870IFE#TRPBF
LTC2870FE
LTC2870FE
28-Lead Plastic TSSOP
28-Lead Plastic TSSOP
0°C to 70°C
–40°C to 85°C
LTC2870CUFD#PBF
LTC2870IUFD#PBF
LTC2870CUFD#TRPBF
LTC2870IUFD#TRPBF
2870
2870
28-Lead (4mm × 5mm) Plastic QFN
28-Lead (4mm × 5mm) Plastic QFN
0°C to 70°C
–40°C to 85°C
LTC2871CFE#PBF
LTC2871IFE#PBF
LTC2871CFE#TRPBF
LTC2871IFE#TRPBF
LTC2871FE
LTC2871FE
38-Lead Plastic TSSOP
38-Lead Plastic TSSOP
0°C to 70°C
–40°C to 85°C
LTC2871CUHF#PBF
LTC2871IUHF#PBF
LTC2871CUHF#TRPBF
LTC2871IUHF#TRPBF
2871
2871
38-Lead (5mm × 7mm) Plastic QFN
38-Lead (5mm × 7mm) Plastic QFN
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
CONFIGURABꢁE TRANSCEIVER COMBINATIONS (RS485 + RS232)
(0 + 0), (1 + 0), (0 + 2)
PACKAGES
28-Lead QFN, 28-Lead TSSOP
38-Lead QFN, 38-Lead TSSOP
LTC2871
(0 + 0), (1 + 0), (1 + 1), (1 + 2), (0 + 1), (0 + 2)
28701f
3
LTC2870/LTC2871
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = Vꢁ = 3.3V, TE485 = 0V, ꢁB = 0V unless otherwise noted.
SYMBOꢁ PARAMETER
Power Supply
CONDITIONS
MIN
TYP
MAX
UNITS
V
Supply Voltage Operating Range
3
5.5
V
V
CC
L
V
Logic Supply Voltage Operating Range
V ≤ V
1.7
V
CC
L
CC
l
V
CC
Supply Current in Shutdown Mode
RXEN = V , DXEN = TE485 = FEN = 0V, (LTC2870)
8
60
μA
L
DX485 = DX232 = TE485 = FEN = H/F = 0V,
RX485 = RX232 = V (LTC2871)
L
V
Supply Current in Transceiver Mode
485/232 = DXEN = V , RXEN = 0V,
3.3
0
mA
μA
CC
L
(Outputs Unloaded) (Note 3)
DY/DZ = 0V or V (LTC2870)
L
DX485 = DX232 = V , RX485 = RX232 = 0V,
L
l
V Supply Current in Transceiver Mode
(Outputs Unloaded)
5
6
L
DI/DIN1/DIN2 = 0V or V (LTC2871)
L
RS485 Driver
l
l
l
|V
OD
|
Differential Output Voltage
R = ∞, V = 3V (Figure 1)
1.5
1.5
2
V
V
V
L
CC
R = 27Ω, V = 3V (Figure 1)
V
L
CC
CC
CC
R = 50Ω, V = 3.13V (Figure 1)
V
L
CC
l
l
Δ|V
|
OD
Difference in Magnitude of Differential Output R = 27ꢀ, V = 3V (Figure 1)
0.2
0.2
V
V
L
CC
Voltage for Complementary Output States
R = 50ꢀ, V = 3.13V (Figure 1)
L CC
l
l
V
Common Mode Output Voltage
R = 27ꢀ or 50ꢀ (Figure 1)
3
V
V
OC
L
Δ|V
|
Difference in Magnitude of Common Mode
Output Voltage for Complementary Output
States
R = 27ꢀ or 50ꢀ (Figure 1)
L
0.2
OC
l
l
I
I
Three-State (High Impedance) Output Current
Maximum Short-Circuit Current
V
= 12V or –7V, V = 0V or 3.3V (Figure 2)
–100
–250
125
250
μA
OZD485
OUT
CC
–7V ≤ V
≤ 12V (Figure 2)
mA
OSD485
OUT
RS485 Receiver
l
l
l
I
Input Current
V
= 12V or –7V, V = 0V or 3.3V (Figure 3)
–100
96
125
μA
kΩ
mV
IN485
IN
CC
(Note 5)
R
Input Resistance
V
IN
= 12V or –7V, V = 0V or 3.3V (Figure 3)
125
IN485
CC
(Note 5)
Differential Input Signal Threshold Voltage
(A-B)
–7V ≤ (A or B) ≤ 12V (Note 5)
200
0
Input Hysteresis
B = 0V (Notes 3, 5)
130
–50
25
mV
mV
mV
V
l
Differential Input Failsafe Threshold Voltage
Input DC Failsafe Hysteresis
Output Low Voltage
–7V ≤ (A or B) ≤ 12V (Note 5)
B = 0V (Note 5)
–200
l
l
l
l
V
V
Output Low, I(RA, RO) = 3mA (Sinking),
3V ≤ V ≤ 5.5V
0.4
0.4
OL
L
Output Low, I(RA, RO) = 1mA (Sinking),
1.7V ≤ V < 3V
V
V
V
L
Output High Voltage
Output High, I(RA, RO) = –3mA (Sourcing),
3V ≤ V ≤ 5.5V
V – 0.4
L
OH
L
Output High, I(RA, RO) = –1mA (Sourcing),
1.7V ≤ V < 3V
V – 0.4
L
L
l
l
Three-State (High Impedance) Output Current 0V ≤ (RA, RO), ≤V , V = 5.5V
0
5
μA
L
L
Short-Circuit Output Current
0V ≤ (RA, RO), ≤V , V = 5.5V
125
mA
L
L
28701f
4
LTC2870/LTC2871
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = Vꢁ = 3.3V, TE485 = 0V, ꢁB = 0V unless otherwise noted.
SYMBOꢁ PARAMETER
Terminating Resistor
CONDITIONS
MIN
TYP
MAX
UNITS
l
R
TE485 = V , A – B = 2V, B = –7V, 0V, 10V
108
120
156
Ω
TERM
L
(Figure 8) (Note 5)
RS232 Driver
l
l
l
V
Output Low Voltage
Output High Voltage
R = 3kΩ; V ≤ –5.9V
–5
5
–5.7
6.2
–7.5
7.5
V
V
OLD
OHD
L
EE
V
R = 3kΩ; V ≥ 6.5V
L
DD
Three-State (High Impedance) Output Current Y or Z (LTC2870) = 15V
RS232 Receiver Enabled
156
μA
l
l
DOUT1 or DOUT2 (LTC2871) = 15V
10
90
μA
Output Short-Circuit Current
RS232 Receiver
Input Threshold Voltage
Driver Output = 0V
35
mA
l
l
l
0.6
0.1
1.5
0.4
2.5
1.0
0.4
V
V
V
Input Hysteresis
Output Low Voltage
I(RA, RB, ROUT1, ROUT2) = 1mA (Sinking)
1.7V ≤ V ≤ 5.5V
L
l
l
Output High Voltage
Input Resistance
I(RA, RB, ROUT1, ROUT2) = –1mA (Sourcing)
V – 0.4
V
L
1.7V ≤ V ≤ 5.5V
L
–15V ≤ (A, B, RIN1, RIN2) ≤ 15V,
RS232 Receiver Enabled
3
5
7
kΩ
l
l
Three-State (High Impedance) Output Current 0V ≤ (RA, RB, ROUT1, ROUT2) ≤ V
0
5
μA
L
Output Short-Circuit Current
V = 5.5V
25
50
mA
L
0V ≤ (RA, RB, ROUT1, ROUT2) ≤ V
L
ꢁogic Inputs
l
l
Threshold Voltage
Input Current
0.4
0.75 • V
5
V
L
0
μA
Power Supply Generator
V
V
Regulated V Output Voltage
RS232 Drivers Enabled, Outputs Loaded with
7
V
V
DD
EE
DD
R = 3kΩ to GND, DIN1/DY = V , DIN2/DZ = 0V
L
L
Regulated V Output Voltage
–6.3
EE
(Note 3)
ESD
LTC2870 Interface Pins (A, B, Y, Z)
Human Body Model to GND or V , Powered or
26
16
kV
kV
CC
Unpowered (Note 7)
LTC2871 Interface Pins (A, B, Y, Z, RIN1, RIN2,
DOUT1, DOUT2)
All Other Pins
Human Body Model (Note 7)
4
kV
28701f
5
LTC2870/LTC2871
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = Vꢁ = 3.3V, TE485 = 0V, ꢁB = 0V unless otherwise noted. Vꢁ ≤ VCC
.
SYMBOꢁ
RS485 AC Characteristics
Maximum Data Rate
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
l
l
(Note 3)
20
Mbps
ns
t
t
Driver Propagation Delay
R
DIFF
= 54Ω, C = 100pF (Figure 4)
20
1
70
6
PLHD485
PHLD485
L
l
Driver Propagation Delay Difference
R
DIFF
= 54Ω, C = 100pF (Figure 4)
ns
L
|t
– t
|
PHLD485
PLHD485
l
l
l
t
t
Driver Skew (Y to Z)
R
R
= 54Ω, C = 100pF (Figure 4)
1
6
15
ns
ns
ns
SKEWD485
DIFF
L
, t
Driver Rise or Fall Time
= 54Ω, C = 100pF (Figure 4)
L
RD485 FD485
DIFF
t
t
, t
,
Driver Output Enable or Disable Time
FEN = V , R = 500Ω, C = 50pF (Figure 5)
120
ZLD485 ZHD485
L
L
L
, t
LZD485 HZD485
l
l
t
t
, t
Driver Enable from Shutdown
Receiver Input to Output
R = 500Ω, C = 50pF (Figure 5)
8
μs
ns
ZHSD485 ZLSD485
L
L
, t
C = 15pF, V = 1.5V, |A – B| = 1.5V
65
1
85
PLHR485 PHLR485
L
CM
(Figure 6) (Note 5)
l
t
Differential Receiver Skew
C = 15pF (Figure 6)
L
6
ns
SKEWR485
|t
– t
|
PHLR485
PLHR485
l
l
t
, t
Receiver Output Rise or Fall Time
C = 15pF (Figure 6)
3
15
50
ns
ns
RR485 FR485
L
t
t
, t
,
Receiver Output Enable or Disable Time FEN = V , R = 1kΩ, C = 15pF (Figure 7)
ZLR485 ZHR485
L
L
L
, t
LZR485 HZR485
l
t
, t
Termination Enable or Disable Time
FEN = V , V = 0V, V = 2V (Figure 8) (Note 5)
100
μs
RTEN485 RTZ485
L
B
AB
RS232 AC Characteristics
Maximum Data Rate
l
l
R = 3kΩ, C = 2500pF
100
500
kbps
kbps
L
L
R = 3kΩ, C = 500pF
L
L
(Note 3)
l
l
Driver Slew Rate (Figure 9)
R = 3kΩ, C = 2500pF
4
V/μs
V/μs
L
L
R = 3kΩ, C = 50pF
30
2
L
L
l
t
t
, t
Driver Propagation Delay
Driver Skew
R = 3kΩ, C = 50pF (Figure 9)
1
μs
ns
μs
PHLD232 PLHD232
L
L
R = 3kΩ, C = 50pF (Figure 9)
50
0.4
SKEWD232
L
L
l
l
t
t
, t
,
Driver Output Enable or Disable Time
FEN = V , R = 3kΩ, C = 50pF (Figure 10)
2
ZLD232 ZHD232
L
L
L
, t
LZD232 HZD232
t
t
t
, t
Receiver Propagation Delay
Receiver Skew
C = 150pF (Figure 11)
L
60
25
60
0.7
200
ns
ns
ns
μs
PHLR232 PLHR232
SKEWR232
C = 150pF (Figure 11)
L
l
l
, t
Receiver Rise or Fall Time
C = 150pF (Figure 11)
L
200
2
RR232 FR232
t
t
, t
,
Receiver Output Enable or Disable Time FEN = V , R = 1kΩ, C = 150pF (Figure 12)
L L L
ZLR232 ZHR232
, t
LZR232 HZR232
Power Supply Generator
l
V /V Supply Rise Time
DD EE
0.2
2
ms
FEN = , (Notes 3 and 4)
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: All currents into device pins are positive; all currents out of device
pins are negative. All voltages are referenced to device ground unless
otherwise specified.
Note 4: Time from FEN until V ≥ 5V and V ≤ –5V. External
components as shown in the Typical Application section.
Note 5: Condition applies to A, B for H/F = 0V, and Y, Z for H/F = V .
Note ꢀ: This IC includes overtemperature protection that is intended
DD
EE
L
to protect the device during momentary overload conditions.
Overtemperature protection activates at a junction temperature exceeding
150°C. Continuous operation above the specified maximum operating
junction temperature may result in device degradation or failure.
Note 3: Guaranteed by other measured parameters and not tested directly.
Note 7: Guaranteed by design and not subject to production test.
28701f
6
LTC2870/LTC2871
TA = 25°C, VCC = Vꢁ = 3.3V, unless otherwise noted.
TYPICAL PERFORMANCE CHARACTERISTICS
VCC Supply Current vs Supply
Voltage in Shutdown Mode
VCC Supply Current vs Supply
Voltage in Fast Enable Mode
VCC Supply Current
vs RS485 Data Rate
100
30
25
20
15
10
5
5
4
3
2
1
V
CC
V
CC
= 5V
= 3.3V
ALL RS485 DRIVERS
AND RECEIVERS
SWITCHING.
ALL DRIVERS AND RECEIVERS DISABLED
TE485 LOW
80
60
40
20
0
CL = 100pF ON EACH
DRIVER OUTPUT.
H/F HIGH
H/F LOW
85°C
25°C
TE HIGH
TE LOW
–40°C
0
0.1
1
10
100
3
3.5
4
4.5
5
5.5
3
3.5
4
4.5
5
5.5
DATA RATE (Mbps)
INPUT VOLTAGE (V)
SUPPLY VOLTAGE (V)
28701 G03
28701 G01
28701 G02
VCC Supply Current vs Supply
Voltage, All Transceivers at Max
Rate (ꢁTC2871)
VCC Supply Current
vs RS232 Data Rate
RS485 Driver Differential Output
Voltage vs Temperature
35
30
25
20
15
10
5
120
110
100
90
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
V
V
= 5V
ALL RS232 DRIVERS
AND RECEIVERS
SWITCHING.
CC
CC
ALL DRIVERS AND
R
= 100ꢀ
L
= 3.3V
RECEIVERS SWITCHING.
DRIVER OUTPUTS TIED TO
RECEIVER INPUTS.
0.5nF
R
= 54ꢀ
L
RS232: 0.5Mbps (CL = 500pF)
RS485: 20Mbps (CL = 100pF)
TE485 HIGH
2.5nF
R
= 100ꢀ
= 54ꢀ
L
2.5nF
0.5nF
R
L
–40°C
25°C
85°C
0.05nF
0.05nF
400 500
80
V
CC
V
CC
= 5V
= 3.3V
70
0
100
200
300
3
3.5
4
4.5
5
5.5
–50
–25
0
25
50
75
100
DATA RATE (kbps)
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
28701 G04
28701 G05
28701 G06
RS485 Driver Propagation Delay
vs Temperature
RS485 Driver Skew
vs Temperature
RS485 Driver Short-Circuit
Current vs Short-Circuit Voltage
50
40
30
20
10
0
3.0
2.5
2.0
1.5
1.0
0.5
0
150
100
50
V
CC
V
CC
= 5V
= 3.3V
V
V
V
V
= 3.3V, V = 1.7V
L
CC
CC
CC
CC
= 5V, V = 1.7V
L
= 3.3V, V = 3.3V
L
= 5V, V = 5V
L
OUTPUT LOW
0
–50
–100
–150
OUTPUT HIGH
10
–50
–25
0
25
50
75
100
–50
–25
0
25
50
75
100
–10
–5
0
5
15
TEMPERATURE (°C)
TEMPERATURE (°C)
SHORT-CIRCUIT VOLTAGE (V)
28701 G06
28701 G08
28701 G09
28701f
7
LTC2870/LTC2871
TA = 25°C, VCC = Vꢁ = 3.3V, unless otherwise noted.
TYPICAL PERFORMANCE CHARACTERISTICS
RS485 Receiver Propagation
Delay vs Temperature
RS485 Receiver Skew
vs Temperature
RS485 Receiver Output Voltage
vs ꢁoad Current
80
70
60
50
40
3.0
2.5
2.0
1.5
1.0
0.5
0
6
V
V
V
= 5V
= 3.3V
= 1.7V
V
CC
V
CC
V
CC
V
CC
= 3.3V, V = 1.7V
L
L
L
L
= 5V, V = 1.7V
L
5
4
3
2
1
0
= 3.3V, V = 3.3V
L
= 5V, V = 5V
L
–50
–25
0
25
50
75
100
–50
–25
0
25
50
75
100
0
2
4
6
8
10
TEMPERATURE (°C)
TEMPERATURE (°C)
OUTPUT CURRENT (mA)
28701 G10
28701 G11
28701 G12
RS232 Receiver Input Threshold
vs Temperature
RS232 Receiver Output Voltage
vs ꢁoad Current
RS485 Termination Resistance
vs Temperature
6
5
4
3
2
1
0
2.0
1.8
1.6
1.4
1.2
1.0
130
128
126
124
122
120
118
116
114
112
110
V
V
V
= 5V
= 3.3V
= 1.7V
L
L
L
V
CM
V
CM
V
CM
= –7V
= 2V
= 12V
INPUT HIGH
INPUT LOW
V
CC
V
CC
= 5V
= 3.3V
0
2
4
6
8
10
–50
–25
0
25
50
75
100
–50
–25
0
25
50
75
100
OUTPUT CURRENT (mA)
TEMPERATURE (°C)
TEMPERATURE (°C)
28701 G14
28701 G13
28701 G15
RS232 Operation at 500kbps
RS485 Operation at 20Mbps
ꢁTC2870 Drivers Changing Modes
DIN1
DIN2
DI
5V/DIV
485/232
Y
Z
Z
DOUT2
DOUT1
1V/DIV
5V/DIV
5V/DIV
5V/DIV
Y
RS232
MODE
RS485
MODE
RS232
MODE
ROUT1
ROUT2
RO
28701 G17
28701 G16
28701 G18
20ns/DIV
1μs/DIV
2μs/DIV
H/F HIGH
Y, Z LOADS: 120ꢀ (DIFF) + 50pF
WRAPPING DATA
DOUT LOADS: 5kꢀ + 50pF
28701f
8
LTC2870/LTC2871
TA = 25°C, VCC = Vꢁ = 3.3V, unless otherwise noted.
TYPICAL PERFORMANCE CHARACTERISTICS
RS232 Driver Outputs Enabling
and Disabling
VDD and VEE Powering Up
VDD and VEE Ripple
VDD RIPPLE
DX232
DOUT1
FEN
2V/DIV
5V/DIV
FEN = 1
FEN = 0
10mV/DIV
5V/DIV
DOUT2
VEE RIPPLE
VDD
DOUT1
DOUT2
VEE
28701 G19
28701 G20
28701 G21
40μs/DIV
TOP CURVES: FAST ENABLE j DX232
BOTTOM CURVES: SHUTDOWN j DX232
40μs/DIV
40μs/DIV
FAST ENABLE MODE,
ALL DRIVERS AND RECEIVERS DISABLED.
PIN FUNCTIONS
ꢁTC2870
QFN
ꢁTC2870
TSSOP
ꢁTC2871
QFN
ꢁTC2871
TSSOP DESCRIPTION
PIN NAME
V
16, 20, 24 19, 23, 27 21, 27, 33 25, 31, 37 Input Supply (3V to 5.5V). Tie all three pins together and connect a 2.2μF or larger
capacitor between V (adjacent to V ) and GND.
CC
CC
DD
V
25
28
35
1
Logic Supply (1.7V to 5.5V) for the receiver outputs, driver inputs, and control inputs.
Bypass this pin to GND with a 0.1μF capacitor if not tied tot V . Keep V ≤ V for
L
CC
L
CC
proper operation. However, V > V will not damage the device, provided that absolute
L
CC
maximum limits are respected.
V
V
15
18
20
24
Generated Positive Supply Voltage for RS232 Driver (+7V). Connect 1ꢁF capacitor
between V and GND.
DD
DD
1, 12, 29
4, 15, 29
1, 12, 16, 5, 16, 20, Generated Negative Supply Voltage for RS232 Driver (–6.3V). Tie all pins together and
19, 39
EE
connect 1ꢁF capacitor between V (adjacent to the CAP pin) and GND.
23, 39
EE
GND
CAP
10, 13,
18, 23
13, 16,
21, 26
14, 17,
25, 32
18, 21, Ground. Tie all four pins together.
29, 36
11
14
15
19
Charge Pump Capacitor for Generated Negative Supply Voltage. Connect a 220nF
capacitor between CAP and SW.
SW
14
22
21
2
17
25
24
5
18
29
28
22
33
32
Switch Pin. Connect 10μH inductor between SW and V .
CC
A
RS485 Positive Receiver Input (Full-Duplex Mode) or RS232 Receiver Input 1 (LTC2870).
RS485 Negative Receiver Input (Full-Duplex Mode) or RS232 Receiver Input 2 (LTC2870).
RS485 Differential Receiver Output or RS232 Receiver Output 1.
RS232 Receiver Output 2.
B
RA
RB
3
6
RO
34
31
30
2
38
35
34
6
RS485 Differential Receiver Output.
RIN1
RIN2
ROUT1
ROUT2
DIN1
DIN2
RS232 Receiver Input 1.
RS232 Receiver Input 2.
RS232 Receiver Output 1.
3
7
RS232 Receiver Output 2.
8
12
13
RS232 Driver Input 1.
9
RS232 Driver Input 2.
28701f
9
LTC2870/LTC2871
PIN FUNCTIONS
ꢁTC2870
QFN
ꢁTC2870
TSSOP
ꢁTC2871
QFN
ꢁTC2871
PIN NAME
DOUT1
DOUT2
DI
TSSOP DESCRIPTION
23
22
7
27
26
11
RS232 Driver Output 1.
RS232 Driver Output 2.
RS485 Driver Input.
DY
7
8
10
11
22
RS485 Driver Input or RS232 Driver Input 1.
RS232 Driver Input 2.
DZ
Y
19
26
24
30
28
RS485 Positive Driver Output. RS232 Driver Output 1 (LTC2870).
RS485 Positive Receiver Input (LTC2870 or LTC2871 in Half-Duplex Mode).
Z
17
4
20
7
RS485 Negative Driver Output or RS232 Driver Output 2 (LTC2870).
RS485 Negative Receiver Input (LTC2870 or LTC2871 in Half-Duplex Mode).
485/232
Interface Select Input. A logic low enables RS232 mode and a high enables RS485 mode.
The mode determines which transceiver inputs and outputs are accessible at the LTC2870
pins as well as which is controlled by the driver and receiver enable pins.
RXEN
DXEN
RX232
RX485
5
6
8
9
Receiver Enable. A logic high disables RS232 and RS485 receivers leaving receiver
outputs Hi-Z. A logic low enables the RS232 or RS485 receivers, depending on the state
of the interface select input 485/232 .
Driver Enable. A logic low disables the RS232 and RS485 drivers leaving the driver output
in a Hi-Z state. A logic high enables the RS232 or RS485 drivers, depending on the state
of the interface select input 485/232.
11
5
15
9
RS232 Receiver Enable. A logic high disables the RS232 receivers and input termination
resistors leaving the RS232 receiver outputs in a Hi-Z state. A logic low enables the
RS232 receivers and resistors, subject to the state of the CH2 pin.
RS485 Receiver Enable. A logic high disables the RS485 receiver leaving the RS485
receiver output in a Hi-Z state. A logic low enables the RS485 receiver and resistors,
subject to the state of the CH2 pin.
DX232
DX485
H/F
10
6
14
10
3
RS232 Driver Enable. A logic low disables the RS232 drivers leaving the RS232 driver
outputs in a Hi-Z state. A logic high enables the RS232 drivers.
RS485 Driver Enable. A logic low disables the RS485 driver leaving the RS485 driver
output in a Hi-Z state. A logic high enables the RS485 driver.
27
2
37
RS485 Half-Duplex Select Input. A logic low is used for full-duplex operation where pins
A and B are the receiver inputs and pins Y and Z are the driver outputs. A logic high is
used for half-duplex operation where pins Y and Z are both the receiver inputs and driver
outputs and pins A and B do not serve as the receiver inputs. The impedance on A and B
and state of differential termination between A and B is independent of the state of H/F.
The H/F pin has no effect on RS232 operation.
TE485
FEN
28
9
3
38
13
4
RS485 Termination Enable. A logic high enables a 120ꢀ resistor between pins A and
B and also between pins Y and Z. A logic low opens the resistors, leaving A/B and Y/Z
unterminated. The LTC2870 termination resistors are never enabled in RS232 mode.
12
17
Fast Enable. A logic high enables fast enable mode. In fast enable mode the integrated
DC/DC converter is active independent of the state of driver, receiver, and termination
enable pins allowing faster circuit enable times than are otherwise possible. A logic low
disables fast enable mode leaving the state of the DC/DC converter dependent on the state
of driver, receiver, and termination enable control inputs. The DC/DC converter powers
down only when FEN is low and all drivers, receivers, and terminators are disabled (refer
to Table 1).
LB
26
1
36
4
2
8
Loopback Enable. A logic high enables logic loopback diagnostic mode, internally routing
the driver input logic levels to the receiver output pins. This applies to both RS232
channels as well as the RS485 driver/receiver. The targeted receiver must be enabled for
the loopback signal to be available on its output. A logic low disables loopback mode. In
Loopback mode, signals are not inverted from driver inputs to receiver outputs.
CH2
RS232 Channel 2 Disable. A logic high disables RS232 receiver 2 and RS232 driver 2
independent of the state of RX232 and DX232 pins. In this state, the disabled driver
output becomes Hi-Z and the 5kΩ load resistor on the disabled receiver input is opened.
A logic low allows both RS232 transceiver channels to be enabled or disabled together
based on the RX232 and DX232 pins.
28701f
10
LTC2870/LTC2871
BLOCK DIAGRAM
ꢁTC2870
1.7V TO 5.5V
(≤ V
)
3V TO 5.5V
2.2μF
CC
220nF
SW
10μH
0.1μF
V
V
CAP
L
CC
DXEN
RXEN
TE485
H/F
V
V
DD
1μF
EE
PULSE-SKIPPING
BOOST
REGULATOR
f = 1.2MHz
RT232
RT485
CONTROL
LOGIC
1μF
485/232
FEN
DRIVERS
LB
232
485
232
DY
DZ
Y
RT485
120Ω
Z
125k
125k
LOOPBACK
PATH
H/F
RECEIVERS
232
RT232
5k
5k
A
B
125k
RT485
RA
RB
485
120Ω
125k
232
2870 BD
GND
28701f
11
LTC2870/LTC2871
BLOCK DIAGRAM
ꢁTC2871
1.7V TO 5.5V
3V TO 5.5V
(≤ V
)
CC
220nF
SW
10μH
0.1μF
2.2μF
V
V
CAP
L
CC
DX232
DX485
RX232
RX485
TE485
H/F
V
V
DD
1μF
EE
PULSE-SKIPPING
BOOST
REGULATOR
f = 1.2MHz
RT232
RT485
CONTROL
LOGIC
CH2
1μF
FEN
DRIVERS
LB
232
485
DIN1
DI
DOUT1
Y
RT485
120Ω
Z
DOUT2
232
DIN2
125k
125k
LOOPBACK
PATH
H/F
RECEIVERS
RT232
ROUT1
RO
232
RIN1
A
5k
5k
125k
125k
RT485
485
120Ω
B
RIN2
232
ROUT2
2871 BD
GND
28701f
12
LTC2870/LTC2871
TEST CIRCUITS
I
, I
OZD485 OSD485
Y OR Z
Z OR Y
Y
Z
R
R
L
L
GND
OR
GND
DY/DI
OR
+
DY/DI
DRIVER
DRIVER
V
OD
V
V
L
L
+
–
V
OUT
–
+
V
OC
–
28701 F02
28701 F01
Figure 1. RS485 Driver DC Characteristics
Figure 2. RS485 Driver Output Current
I
IN485
A OR B
B OR A
RECEIVER
+
–
V
IN
V
IN
R
=
IN485
I
28701 F03
IN485
Figure 3. RS485 Receiver Input Current and Resistance (Note 5)
V
L
t
t
PLHD485
DY/DI
Y, Z
PLHD485
Y
Z
0V
t
SKEWD485
C
C
L
L
DY/DI
V
½V
OD
OD
R
DRIVER
DIFF
90%
10%
90%
10%
0V
0V
Y - Z
t
t
FD485
RD485
28701 F04
Figure 4. RS485 Driver Timing Measurement
28701f
13
LTC2870/LTC2871
TEST CIRCUITS
V
L
GND
OR
R
L
DXEN/
DX485
½V
½V
L
L
t
,
ZLD485
0V
V
Y
Z
V
CC
t
t
t
LZD485
ZLSD485
C
C
L
CC
V
OR
GND
L
DY/DI
½V
½V
Y OR Z
Z OR Y
CC
CC
DRIVER
0.5V
0.5V
V
V
OL
OH
R
V
OR
L
CC
DXEN/DX485
0V
GND
t
,
HZD485
ZHD485
t
L
ZHSD485
28701 F05
Figure 5. RS485 Driver Enable and Disable Timing Measurements
V
AB
0V
A-B
V
V
/2
/2
A
B
AB
AB
–V
AB
t
t
PLHR485
PHLR485
RA/RO
V
CM
V
RECEIVER
L
90%
10%
90%
RA/RO
½V
½V
L
C
L
L
10%
t
0V
t
RR485
FR485
t
= t
– t
SKEWR485 PLHR485 PHLR485
28701 F06
Figure ꢀ. RS485 Receiver Propagation Delay Measurements (Note 5)
V
L
RXEN/
½V
½V
L
L
RX485
t
ZLR485
0V
t
t
A
B
LZR485
V
L
0V TO 3V
3V TO 0V
V
OR
GND
R
L
L
RA/RO
½V
½V
RA/RO
L
L
RECEIVER
0.5V
0.5V
V
V
OL
OH
C
L
RXEN/RX485
RA/RO
0V
t
HZR485
ZHR485
28701 F07
Figure 7. RS485 Receiver Enable and Disable Timing Measurements (Note 5)
28701f
14
LTC2870/LTC2871
TEST CIRCUITS
V
I
AB
A
R
=
TERM
V
L
I
A
TE485
½V
½V
L
L
A
B
+
–
0V
RECEIVER
V
V
AB
t
t
RTZ485
RTEN485
90%
I
TE485
A
10%
+
–
B
28701 F08
Figure 8. RS485 Termination Resistance and Timing Measurements (Note 5)
V
L
t
DRIVER
INPUT
DRIVER
OUTPUT
PHLD232
DRIVER
INPUT
½V
½V
L
L
t
PLHD232
0V
t
t
R
F
V
V
OHD
OLD
R
L
C
L
3V
3V
–3V
DRIVER
INPUT
0V
0V
–3V
6V
t
= |t
– t
|
SLEW RATE =
SKEWD232
PHLD232 PLHD232
t
F
OR t
R
28701 F09
Figure 9. RS232 Driver Timing and Slew Rate Measurements
V
L
DRIVER
OUTPUT
DXEN/
DX232
½V
½V
L
L
0V OR V
0V
L
t
t
HZD232
ZHD232
DXEN/DX232
R
C
L
L
V
OHD
0.5V
0.5V
DRIVER
OUTPUT
5V
5V
0V
0V
t
t
LZD232
ZLD232
DRIVER
OUTPUT
V
OLD
28701 F10
Figure 10. RS232 Driver Enable and Disable Times
28701f
15
LTC2870/LTC2871
TEST CIRCUITS
+3V
–3V
RECEIVER
INPUT
RECEIVER
INPUT
RECEIVER
OUTPUT
1.5V
1.5V
t
t
PLHR232
PHLR232
V
C
L
L
90%
10%
90%
10%
RECEIVER
OUTPUT
½V
½V
L
L
0V
t
t
RR232
FR232
t
= |t
– t
|
SKEWR232
PLHR232 PHLR232
28701 F11
Figure 11. RS232 Receiver Timing Measurements
V
L
RECEIVER
OUTPUT
RXEN/
R
½V
½V
L
L
L
GND
OR V
RX232
–3V OR +3V
0V
L
t
t
HZR232
ZHR232
RXEN/RX232
C
L
V
OHR
0.5V
0.5V
RECEIVER
OUTPUT
½V
½V
L
L
0V
t
t
LZR232
ZLR232
V
L
RECEIVER
OUTPUT
V
OLR
28701 F12
Figure 12. RS232 Receiver Enable and Disable Times
28701f
16
LTC2870/LTC2871
FUNCTION TABLES
Table 1. ꢁTC2870 Mode Selection Table
DC/DC
FEN
0
485/232
RXEN
DXEN
TE485
H/F ꢁB CONVERTER MODE AND COMMENTS
X
0
X
0
0
1
1
1
1
1
1
0
1
1
1
X
0
X
0
X
X
X
0
0
0
0
0
1
X
1
X
X
X
X
X
X
0
X
0
X
X
X
X
1
X
X
X
X
X
X
X
X
X
X
X
X
0
1
X
X
X
X
X
0
0
0
0
X
0
0
1
1
OFF
OFF
ON
ON
ON
ON
ON
ON
X
Low Power Shutdown: All Main Functions Off
0
Low Power Shutdown: All Main Functions Off
Fast-Enable: DC/DC Converter On Only
RS232 Drivers On
1
X
X
RS232 Receivers On
X
RS485 Driver On
X
RS485 Receiver On
X
RS485 Driver and Receiver 120Ω Termination Enabled
RS485 Full-Duplex Mode
X
X
X
RS485 Half-Duplex Mode
X
ON
ON
RS485 Loopback Mode
X
RS232 Loopback Mode
Table 2. ꢁTC2871 Mode Selection Table (CH2 = 0)
DC/DC
H/F ꢁB CONVERTER MODE AND COMMENTS
FEN
0
RX232
DX232
RX485
DX485
TE485
1
1
X
0
X
X
X
X
X
0
0
0
1
X
X
X
X
X
X
X
1
1
X
X
X
0
X
X
0
X
0
0
X
X
1
X
X
X
X
X
0
0
X
X
X
X
X
X
X
X
X
X
X
X
X
X
0
1
X
X
X
X
0
0
0
0
0
0
1
1
OFF
ON
ON
ON
ON
ON
X
Low Power Shutdown: All Main Functions Off
Fast-Enable: DC/DC Converter On Only
RS232 Drivers On
1
X
X
RS232 Receivers On
X
RS485 Driver On
X
RS485 Receiver On
X
RS485 Full-Duplex Mode
RS485 Half-Duplex Mode
RS485 Loopback Mode
RS232 Loopback Mode
X
X
X
ON
ON
X
Table 3. RS232 Receiver Mode (485/232 = 0 for ꢁTC2870, CH2 = 0 for ꢁTC2871)
RECEIVER INPUTS
(A, B, RIN1, RIN2)
RECEIVER OUTPUTS
ꢁTC2870 RECEIVER INPUTS ꢁTC2871 RECEIVER INPUTS
RX232 OR RXEN
CONDITIONS
No Fault
(RA, RB, ROUT1, ROUT2)
(A, B)
125kΩ
5kΩ
(RIN1, RIN2)
1
0
0
0
X
0
1
X
Hi-Z
1
Hi-Z
No Fault
5kΩ
No Fault
0
5kΩ
5kΩ
Thermal Fault
Hi-Z
5kΩ
5kΩ
Table 4. RS232 Driver Mode (485/232 = 0 for ꢁTC2870, CH2 = 0 for ꢁTC2871)
DRIVER INPUTS
ꢁTC2870 DRIVER OUTPUTS
(Y, Z)
ꢁTC2871 DRIVER OUTPUTS
(DOUT1, DOUT2)
DX232 OR DXEN
(DY, DZ, DIN1, DIN2)
CONDITIONS
No Fault
0
1
1
X
X
0
1
X
125kΩ
Hi-Z
1
No Fault
1
0
No Fault
0
Thermal Fault
125kΩ
Hi-Z
28701f
17
LTC2870/LTC2871
FUNCTION TABLES
Table 5. ꢁTC2871 CH2 CONTROꢁ
RS232 RECEIVER INPUTS
RS232 DRIVER OUTPUTS
CH2
X
DX232
RX232
RIN1
Hi-Z
5kΩ
Hi-Z
5kΩ
5kΩ
Hi-Z
5kΩ
RIN2
Hi-Z
5kΩ
Hi-Z
5kΩ
Hi-Z
Hi-Z
Hi-Z
DOUT1
Hi-Z
DOUT2
Hi-Z
COMMENTS
0
0
1
1
0
1
1
1
0
1
0
0
1
0
Both Drivers and Receivers Disabled
Both Receivers Enabled, Both Drivers Disabled
Both Receivers Disabled, Both Drivers Enabled
Both Receivers and Drivers Enabled
Channel 2 Drivers and Receivers Disabled
Channel 2 Drivers and Receivers Disabled
Channel 2 Drivers and Receivers Disabled
0
Hi-Z
Hi-Z
0
Driven
Driven
Hi-Z
Driven
Driven
Hi-Z
0
1
1
Driven
Driven
Hi-Z
1
Hi-Z
Table ꢀ. RS485 Driver Mode (TE485 = 0)
DX485 OR DXEN
DI
X
0
CONDITIONS
No Fault
Y
125kΩ
0
Z
0
1
1
X
125kΩ
No Fault
1
0
1
No Fault
1
X
Thermal Fault
125kΩ
125kΩ
Table 7. RS485 Receiver Mode (ꢁB = 0)
RXEN OR RX485
A - B (NOTE 5)
CONDITIONS
RA, RO
1
0
0
0
X
X
No Fault
No Fault
Hi-Z
0
< –200mV
> 200mV
No Fault
1
Inputs Open or Shorted Together (DC)
X
Failsafe
1
Thermal Fault
Hi-Z
Table 8. RS485 Termination (485/232 = 1 for ꢁTC2870)
TE485
H/F, ꢁB
CONDITIONS
No Fault
R (A TO B)
Hi-Z
R (Y TO Z)
Hi-Z
0
1
X
X
X
X
No Fault
120Ω
Hi-Z
120Ω
Hi-Z
Thermal Fault
Table 9. RS485 Duplex Control (485/232 = 1 for ꢁTC2870)
H/F
0
RS485 DRIVER OUTPUTS
RS485 RECEIVER INPUTS
Y, Z
Y, Z
A, B
Y, Z
1
Table 10. ꢁTC2870 ꢁoopback Functions
Table 11. ꢁTC2871 ꢁoopback Functions
ꢁB
0
RXEN
MODE
Not Loopback
ꢁB
0
RX232 RX485
MODE
Not Loopback
X
1
0
X
1
0
1
0
X
1
1
0
0
X
Not Loopback
X
1
Not Loopback
1
Loopback (RA = DY, RB = DZ)
Loopback RS232 (ROUT1 = DIN1, ROUT2 = DIN2)
Loopback RS485 (R0 = DI)
1
1
Loopback All (ROUT1 = DIN1, ROUT2 = DIN2, RO = DI)
28701f
18
LTC2870/LTC2871
APPLICATIONS INFORMATION
Overview
C1
L1
3V TO 5.5V
C4
220nF
10μH
TheLTC2870andLTC2871areflexiblemultiprotocoltrans-
ceivers supporting RS485/RS422 and RS232 protocols.
These parts can be powered from a single 3V to 5.5V
supply with optional logic interface supply as low as 1.7V.
An integrated DC/DC converter provides the positive and
negative supply rails needed for RS232 operation. Auto-
maticallyselectedintegratedterminationresistorsforboth
RS232 and RS485 protocols are included, eliminating the
need for external components and switching relays. Both
parts include loopback control for self-test and debug as
well as logically-switchable half- and full-duplex control
of the RS485 bus interface.
2.2μF
V
SW
CAP
CC
V
V
DD
C2
1μF
PULSE-SKIPPING
BOOST
REGULATOR
f = 1.2MHz
EE
C3
1μF
28701 F13
Figure 13. DC/DC Converter
The LTC2870 offers a single port that can be configured
as either two RS232 receivers and drivers or one RS485/
RS422 receiver and driver depending on the state of the
485/232 pin. Control inputs DXEN and RXEN provide
independent control of driver and receiver operation for
either RS232 or RS485 transceivers, depending on the
selected operating protocol.
The DC/DC converter requires a 10μH inductor (L1) and a
bypasscapacitor(C4)of2.2μF.Thechargepumpcapacitor
(C1) is 220nF and the storage capacitors (C2 and C3) are
1μF. Larger storage capacitors up to 4.7μF may be used if
C1 and C4 are scaled proportionately. Locate C1–C4 close
to their associated pins.
Up to two LTC2870 or LTC2871 devices can be powered
from one of the devices; see Figure 48 in the Typical Ap-
plications section.
TheLTC2871separatestheRS232andRS485transceivers
into independent I/Os allowing simultaneous operation
of two RS232 transceivers and one RS485 transceiver.
Independent control over driver and receiver mode for
eachprotocolisprovidedwithlogicinputsDX232,RX232,
DX485,RX485.SinglechannelRS232operationispossible
via the CH2 control pin. The disabled channel maintains a
Hi-Z state on the receiver input and driver output, allowing
these lines to be shared with other transceivers.
Inductor Selection
A 10ꢁH inductor with a saturation current (I ) rating
SAT
of at least 220mA and a DCR (copper wire resistance) of
less than 1.3Ω is required. Some small inductors meeting
these requirements are listed in Table 12.
Table 12. Recommended Inductors
Both parts feature rugged operation with ESD ratings
of 26kV (LTC2870) and 16kV (LTC2871) HBM on the
RS232andRS485receiverinputsanddriveroutputs,both
unpowered and powered. All other pins offer protection
exceeding 4kV.
I
MAX
SAT
PART NUMBER
(mA) DCR (Ω)
SIZE(mm)
MANUFACTURER
LBC2016T100K
CBC2016T100M
245
380
1.07
1.07
2 × 1.6 × 1.6 Taiyo Yuden
2 × 1.6 × 1.6 www.t-yuden.com
FSLB2520-100K
220
1.1
2.5 × 2 × 1.6 Toko
www.tokoam.com
DC/DC Converter
Capacitor Selection
Theon-chipDC/DCconverteroperatesfromtheV input,
generating a 7V V supply and a charge pumped –6.3V
CC
The small size of ceramic capacitors makes them ideal
for the LTC2870 and LTC2871. Use X5R or X7R dielectric
types; their ESR is low and they retain their capacitance
over relatively wide voltage and temperature ranges. Use
a voltage rating of at least 10V.
DD
V
supply, as shown in Figure 13. V and V power
EE
DD EE
the output stage of the RS232 drivers and are regulated
to levels that guarantee greater than 5V output swing.
28701f
19
LTC2870/LTC2871
APPLICATIONS INFORMATION
Inrush Current and Supply Overshoot Precaution
Incertainapplicationsfastsupplyslewratesaregenerated
V ꢁogic Supply and ꢁogic Pins
ꢁ
A separate logic supply pin V allows the LTC2870 and
L
when power is connected. If the V voltage is greater
LTC2871 to interface with any logic signal from 1.7V to
CC
than 4.5V and its rise time is faster than 10ꢁs, the pins
5.5V. All logic I/Os use V as their high supply. For proper
L
V
and SW can exceed their absolute maximum values
operation, V should not be greater than V . During
L CC
DD
duringstart-up. WhensupplyvoltageisappliedtoV , the
power-up, if V is higher than V , the device will not be
CC
L CC
voltage difference between V and V generates inrush
damaged, but behavior of the device is not guaranteed.
CC
DD
currentflowingthroughinductorL1andcapacitorsC1and
C2. The peak inrush current must not exceed 2A. To avoid
this condition, add a 1Ω resistor as shown in Figure 14.
This precaution is not relevant for supply voltages below
4.5V or rise times longer than 10ꢁs.
If V is not connected to V , bypass V with a 0.1μF
L
CC
L
capacitor to GND.
RS232 and RS485 driver outputs are undriven and the
RS485 termination resistors are disabled when V or V
L
CC
is grounded or V is disconnected.
CC
Although all logic input pins reference V as their high
L
5V
supply, they can be driven up to 7V, independent of V and
L
0V
≤10μs
V , with the exception of FEN, which must not exceed V
CC L
by more than 1V for proper operation. Logic input pins
do not have internal biasing devices to pull them up or
down. They must be driven high or low to establish valid
logic levels; do not float.
R1
C1
220nF
L1
1Ω
10μH
1/8W
INRUSH
CURRENT
C4
2.2μF
SW
CAP
GND
RS485 Driver
V
CC
The RS485 driver provides full RS485/RS422 compati-
bility. When enabled, if DI is high, Y – Z is positive. With
the driver disabled the Y and Z output resistance is greater
than 96kΩ (typically 125kΩ) to ground over the entire
common mode range of –7V to +12V. This resistance is
equivalent to the input resistance on these lines when the
driver is configured in half-duplex mode and Y and Z act
as the RS485 receiver inputs.
28701 F14
V
DD
C2
1μF
Figure 14. Supply Current Overshoot Protection
for Input Supplies of 4.5V of Higher
Driver Overvoltage and Overcurrent Protection
The RS232 and RS485 driver outputs are protected from
short circuits to any voltage within the absolute maximum
range 15V.Themaximumcurrentinthisconditionis90mA
for the RS232 driver and 250mA for the RS485 driver.
If the RS485 driver output is shorted to a voltage greater
thanV , whenitisactive, positivecurrentofupto100mA
CC
may flow from the driver output back to V . If the system
CC
power supply or loading cannot sink this excess current,
clamp V to GND with a Zener diode (e.g., 5.6V, 1W,
CC
1N4734) to prevent an overvoltage condition on V .
CC
28701f
20
LTC2870/LTC2871
APPLICATIONS INFORMATION
All devices also feature thermal shutdown protection that
disables the drivers, receivers, and RS485 terminators in
case of excessive power dissipation (see Note 6).
less than approximately 2μs. Increasingly slower signals
will have increasingly less effective hysteresis, limited by
the DC failsafe value of about 25mV.
The LTC2870 and LTC2871 provide full failsafe operation
that guarantees the receiver output will be a logic high
state when the inputs are shorted, left open, or terminated
but not driven, for more than about 2μs. The delay allows
normal data signals to transition through the threshold
region without being interpreted as a failsafe condition.
RS485 Balanced Receiver with Full Failsafe Operation
The LTC2870 and LTC2871 receivers use a window com-
parator with two voltage thresholds centered around zero
forlowpulsewidthdistortion.AsillustratedinFigure15,for
adifferentialsignalapproachingfromanegativedirection,
the threshold is typically +65mV. When approaching from
thepositivedirection,thethresholdistypically–65mV.Each
of these thresholds has about 25mV of hysteresis (not
shown in the figure). The state of RO reflects the polarity
of A–B in full-duplex mode or Y–Z in half-duplex mode.
RS485 Biasing Resistors Not Required
RS485 networks are often biased with a resistive divider
to generate a differential voltage of ≥200mV on the data
lines, which establishes a logic high state when all the
transmitters on the network are disabled. The values of
the biasing resistors depend on the number and type
of transceivers on the line and the number and value of
terminating resistors. Therefore the values of the biasing
resistors must be customized to each specific network
installation, and may change if nodes are added to or
removed from the network.
This windowing around 0V preserves pulse width and
duty cycle for small input signals with heavily slewed
edges, typical of what might be seen at the end of a very
long cable. This performance is highlighted in Figure 16,
whereasignalisdriventhrough4000feetofCAT5ecableat
3Mbps.Eventhoughthedifferentialsignalpeaksatjustover
100mVandisheavilyslewed,theoutputmaintainsanearly
perfect signal with almost no duty cycle distortion.
The internal failsafe feature of the LTC2870 and LTC2871
eliminates the need for external biasing resistors. The
LTC2870 and LTC2871 transceivers will operate correctly
on unbiased, biased or underbiased networks.
Anadditionalbenefitofthewindowcomparatorarchitecture
is excellent noise immunity due to the wide effective dif-
ferentialhysteresis(or‘AC’hysteresis)ofabout130mVfor
normalsignalstransitioningthroughthewindowregionin
B
0.1V/DIV
A
RO
(A-B)
RECEIVER
OUTPUT HIGH
0.1V/DIV
RECEIVER
RO
OUTPUT LOW
5V/DIV
V
AB
–200mV
–65mV 0V
65mV
200mV
28701 F16
28701 F15
200ns/DIV
Figure 1ꢀ. A 3Mbps Signal Driven Down 4000ft of CAT 5e
Cable. Top Traces: Received Signals After Transmission
Through Cable; Middle Trace: Math Showing Differences
of Top Two Signals; Bottom Trace: Receiver Output
Figure 15. RS485 Receiver Input Threshold Characteristics
28701f
21
LTC2870/LTC2871
APPLICATIONS INFORMATION
Receiver Outputs
through logic control, the proper line termination for cor-
rect operation when configuring transceiver networks.
Termination should be enabled on transceivers positioned
at both ends of the network bus. Termination on the driver
nodes is important for cases where the driver is disabled
but there is communication on the connecting bus from
another node. Differential termination resistors are never
enabled in RS232 mode on the LTC2870.
The RS232 and RS485 receiver outputs are internally
driven high (to V ) or low (to GND) with no external pull-
L
up needed. When the receivers are disabled the output pin
becomes Hi-Z with leakage of less than 5ꢁA for voltages
within the V supply range.
L
RS485 Receiver Input Resistance
When the TE485 pin is high, the termination resistors are
enabled and the differential resistance from A to B and Y
to Z is 120Ω. The resistance is maintained over the entire
RS485 common mode range of –7V to 12V as shown in
Figure 18.
The RS485 receiver input resistance from A or B to GND
(Y or Z to GND in half-duplex mode with driver disabled) is
greater than 96kΩ (typically 125kΩ) when the integrated
termination is disabled. This permits up to a total of 256
receiverspersystemwithoutexceedingtheRS485receiver
loading specification. The input resistance of the receiver
isunaffectedbyenabling/disablingthereceiverorwhether
the part is in half-duplex, full-duplex, loopback mode, or
even unpowered. The equivalent input resistance looking
into the RS485 receiver pins is shown in Figure 17.
126
V
CC
V
CC
= 5.0V
= 3.3V
124
122
120
118
116
125k
A
60Ω
TE485
–10
–5
0
5
10
15
VOLTAGE (V)
60Ω
125k
28701 F18
B
Figure 18. Typical Resistance of the Enabled RS485
Terminator vs Common Mode Voltage on A /B
28701 F17
Figure 17: Equivalent RS485 Receiver
Input Resistance Into A and B (Note 5)
RS485 Half- and Full-Duplex Control
The LTC2870 and LTC2871 are equipped with a control to
switch between half- and full-duplex operation. With the
H/F pin set to a logic low, the A and B pins serve as the
differential receiver inputs. With the H/F pin set to a logic
high, the Y and Z pins serve as the differential inputs. In
either configuration, the RS485 driver outputs are always
on Y and Z. The impedance looking into the A and B pins
is not affected by H/F control, including the differential
termination resistance. The H/F control does not affect
RS232 operation.
Selectable RS485 Termination
Propercableterminationisimportantforgoodsignalfidel-
ity. When the cable is not terminated with its characteristic
impedance, reflections cause waveform distortion.
The LTC2870 and LTC2871 offer integrated switchable
120Ωterminationresistorsbetweenthedifferentialreceiver
inputs and also between the differential driver outputs.
Thisprovidestheadvantageofbeingabletoeasilychange,
28701f
22
LTC2870/LTC2871
APPLICATIONS INFORMATION
ꢁogic ꢁoopback
The solid vertical line represents the specified maximum
datarateintheRS485/RS422standards. Thedashedlines
at 20Mbps show the maximum data rates of the LTC2870
and LTC2871.
A loopback mode connects the driver inputs to the re-
ceiver outputs (non-inverting) for self test. This applies to
both RS232 and RS485 transceivers. Loopback mode is
entered when the LB pin is high and the relevant receiver
is enabled.
ꢁayout Considerations
All V pins must be connected together on the PC board
CC
In loopback mode, the drivers function normally. They can
be disabled with outputs in a Hi-Z state or left enabled to
allow loopback testing in normal operation. Loopback
works in half- or full-duplex mode and does not affect the
termination resistors.
with very low impedance traces or with a dedicated plane.
A 2.2μF or larger decoupling capacitor (C4 in Figure 13)
must be placed less than 0.7cm away from the V pin
CC
that is adjacent to the V pin.
DD
0.1μF capacitors to GND can be added on the V pins
CC
10k
adjacent to the B and V pins if the connection to the 2.2μF
L
decoupling capacitor is not direct or if the trace is very
narrow. All GND pins must be connected together and
1k
all V pins must be connected together, including the
EE
exposed pad on the bottom of the package. The bypass
LTC2870/LTC2871
MAX DATA RATE
capacitor at V , C3, should be positioned closest to the
EE
V
EE
pin that is adjacent to the CAP pin, with no more than
1cm of total trace length between the V and GND pins.
100
EE
RS485/RS422
MAX DATA RATE
Place the charge pump capacitor, C1, directly adjacent to
the SW and CAP pins, with no more than one centimeter
of total trace length to maintain low inductance. Close
placement of the inductor, L1, is of secondary importance
compared to the placement of C1 but should include no
more than two centimeters of total trace length.
10
10k
100k
1M
10M
100M
DATA RATE (bps)
28701 F19
Figure 19. Cable ꢁength vs Data Rate (RS485/RS422
Standard Shown in Vertical Solid ꢁine)
The PC board traces connected to high speed signals A/B
and Y/Z should be symmetrical and as short as possible
to minimize capacitive imbalance and maintain good dif-
ferential signal integrity. To minimize capacitive loading
effects, the differential signals should be separated by
more than the width of a trace.
RS485 Cable ꢁength vs Data Rate
For a given data rate, the maximum transmission dis-
tance is bounded by the cable properties. A typical curve
of cable length vs data rate compliant with the RS485/
RS422 standards is shown in Figure 19. Three regions
of this curve reflect different performance limiting fac-
tors in data transmission. In the flat region of the curve,
maximum distance is determined by resistive losses in
the cable. The downward sloping region represents limits
in distance and data rate due to AC losses in the cable.
Route outputs away from sensitive inputs to reduce
feedback effects that might cause noise, jitter, or even
oscillations. For example, do not route DI or A/B near the
driver or receiver outputs.
28701f
23
LTC2870/LTC2871
TYPICAL APPLICATIONS
VCC = 3V to 5.5V, Vꢁ = 1.7V to VCC. ꢁogic input pins not shown are tied to a valid logic state.
V
V
L
V
L
L
LTC2870
LTC2870
LTC2870
485/232
RXEN
H/F
485/232
RXEN
LB
DXEN
LB
DXEN
DXEN
RXEN
485/232
TE485
LB
DY
RA
Y
A
Y
DY
RA
Y
A
DY
120Ω
Z
DZ
RB
Z
DZ
RB
Z
A
B
RA
120Ω
B
B
GND
GND
GND
28701 F21
28701 F22
28701 F20
Figure 20. ꢁTC2870 in
RS232 Mode
Figure 21. ꢁTC2870 in RS232
Mode with ꢁoopback
Figure 22. ꢁTC2870 in RS485
Mode, Terminated
V
L
V
L
V
L
LTC2870
LTC2870
LTC2870
RXEN
DXEN
485/232
LB
RXEN
DXEN
RXEN
DXEN
485/232
LB
TE485
LB
485/232
H/F
H/F
TE485
H/F
TE485
Y
Z
Y
Z
DY
RA
DY
RA
Y
DY
RA
120ꢀ
Z
A
B
A
120ꢀ
B
GND
GND
GND
28701 F24
28701 F23
28701 F25
Figure 23. ꢁTC2870 in RS485
Mode in ꢁoopback
Figure 24. ꢁTC2870 in RS485
Mode Half-Duplex
Figure 25. ꢁTC2870 in RS485
Mode, Half-Duplex, with
ꢁoopback and Terminated
28701f
24
LTC2870/LTC2871
TYPICAL APPLICATIONS
VCC = 3V to 5.5V, Vꢁ = 1.7V to VCC. ꢁogic input pins not shown are tied to a valid logic state.
V
L
V
L
V
L
LTC2870
LTC2871
LTC2871
RXEN
H/F
DX485
DX232
DX232
DXEN
TE485
DX485
RX232
RX485
RX485
CH2
RX232
LB
CH2
TE485
H/F
TE485
H/F
485/232
RS RS
232 485
LB
LB
DY
Y
Y
Z
A
B
DI
120Ω
Z
DIN1
DOUT1
RIN1
DZ
RA
ROUT1
A
RO
DIN2
DOUT2
RIN2
ROUT2
120Ω
B
RB
GND
GND
GND
28701 F26
28701 F28
28701 F27
Figure 2ꢀ. ꢁTC2870 Protocol Switching
Figure 27. ꢁTC2871 in RS485 Mode
Figure 28. ꢁTC2871 in RS232 Mode
V
L
V
L
V
L
LTC2871
LTC2871
LTC2871
RX232
RX232
DX232
DX485
DX232
DX232
DX485
LB
CH2
RX485
TE485
H/F
RX232
RX485
DX485
CH2
RX485
H/F
TE485
CH2
H/F
TE485
LB
LB
Y
Y
DI
120Ω
Z
DI
Z
A
RO
A
120Ω
B
RO
DIN1
DOUT1
RIN1
B
DIN1
DOUT1
ROUT1
DIN1
DOUT1
RIN1
ROUT1
DIN2
ROUT1
RIN1
DOUT2
DIN2
DOUT2
RIN2
ROUT2
RIN2
ROUT2
GND
GND
GND
28701 F30
28701 F29
28701 F31
Figure 29. ꢁTC2871 Single
RS232 Channel Active
Figure 30. ꢁTC2871 in
RS485 and RS232 Mode
Figure 31. ꢁTC2871 in RS485 and
RS232 Mode with ꢁoopback and
RS485 Termination
28701f
25
LTC2870/LTC2871
TYPICAL APPLICATIONS
VCC = 3V to 5.5V, Vꢁ = 1.7V to VCC. ꢁogic input pins not shown are tied to a valid logic state.
V
L
V
V
L
L
LTC2871
LTC2871
LTC2871
CH2
LB
RX232
CH2
H/F
DX232
DX485
H/F
RX232
CH2
DX232
DX485
H/F
TE485
RX485
LB
RX485
TE485
TE485
D R 485
D R 232
DX485
RX485
DX232
LB
RX232
Y
Z
Y
Z
Y
DI
DI
DI
120Ω
Z
A
RO
RO
RO
120Ω
B
DIN1
DOUT1
DIN1
DIN1
DOUT1
RIN1
DOUT1
RIN1
RIN1
ROUT1
DIN2
ROUT1
DIN2
ROUT1
DIN2
DOUT2
DOUT2
RIN2
DOUT2
RIN2
ROUT2
ROUT2
RIN2
ROUT2
GND
GND
GND
28701 F32
28701 F34
28701 F33
Figure 32. ꢁTC2871 in RS485 and
RS232 Mode, Both Half-Duplex
Figure 33. ꢁTC2871 in RS485 and RS232
Mode, RS485 Half-Duplex, ꢁoopback
Figure 34. ꢁTC2871 in RS485
and RS232 Mode, RS485
Half-Duplex, Terminated
V
L
LTC2870/
LTC2871
H/F
485/232
3V TO 5.5V
LB
TE485
1.7V TO V
LTC2870/
LTC2871
CC
V
V
CC
L
LTC2870/
LTC2871
CONTROL
SIGNALS
Y
DY, DIN1
Y
A
DI
120Ω
Z
DY
RS232
μP
RA, ROUT1
RS485
FULL HALF
DUPLEX
H/F
DZ, DIN2
Z
28701 F37
RB, ROUT2
B
A
C
L
3k
DATA RATE
C
L
RO
RB
120Ω
100kbps 5nF
500kbps 1nF
GND
B
28701 F36
GND
Figure 37. Driving ꢁarger
RS232 ꢁoads
Figure 3ꢀ. Microprocessor Interface
28701 F35
Figure 35. RS485 Duplex Switching
28701f
26
LTC2870/LTC2871
TYPICAL APPLICATIONS
1.7V TO V
CC
3V TO 5.5V
V
L
LTC2870
V
V
L
CC
DXEN
RXEN
485/232
RS485
RS485
RS232
H/F
FULL-DUPLEX HALF-DUPLEX FULL-DUPLEX
TE485
485/232 = 1
H/F = 0
485/232 = 1
H/F = 1
485/232 = 0
H/F = X
DY
RS485
RS485
RS485
RS485
RS232
RS232
Y
Z
CONTROLLER
DZ
RA
CONNECTOR
RS485
RS485
RS232
RS232
A
B
RB
GND
28701 F38
Figure 38. ꢁTC2870: Making Use of Shared I/O for Various Communication Configurations
1.7V TO V
CC
3V TO 5.5V
V
LTC2870
L
V
V
CC
L
DXEN
TE485
RXEN
485/232
RS485
RS232
H/F
HALF-DUPLEX HALF-DUPLEX
485/232 = 1
H/F = 0
485/232 = 0
H/F = X
DY
RS485
RS485
RS232
RS232
Y
Z
CONNECTOR
CONTROLLER
DZ
RA
A
B
RB
GND
28701 F39
Figure 39. ꢁTC2870: Using External Connections for Half-Duplex RS232 or RS485 Operation
28701f
27
LTC2870/LTC2871
TYPICAL APPLICATIONS
1.7V TO V
CC
3V TO 5.5V
V
L
V
CC
V
L
LTC2871
RS232
RS232
DX232
RX232
DX485
RX485
H/F
FULL-DUPLEX FULL-DUPLEX
RS485
RS485
FULL-DUPLEX HALF-DUPLEX
H/F = 0
H/F = 1
TE485
RS232
RS232
DOUT1
DIN1
RS485
RS485
RS485
RS485
Y
Z
DI
CONTROLLER
RS232
RS232
DOUT2
RIN1
DIN2
CONNECTOR
RS232
RS232
ROUT1
RS485
RS485
A
B
RO
RS232
RS232
ROUT2
RIN2
GND
28701 F40
Figure 40. ꢁTC2871: Various Communication Configurations
1.7V TO V
CC
3V TO 5.5V
V
L
V
CC
V
LTC2871
RS232
RS232
L
HALF-DUPLEX HALF-DUPLEX
DX232
RX232
DX485
RX485
H/F
TE485
DIN1
RS485
RS485
FULL-DUPLEX HALF-DUPLEX
H/F = 0
H/F = 1
RS232
RS232
DOUT1
RS485
RS485
RS485
RS485
Y
Z
DI
CONTROLLER
RS232
RS232
DOUT2
RIN1
DIN2
CONNECTOR
ROUT1
RS485
RS485
A
B
RO
RIN2
ROUT2
GND
28701 F41
Figure 41. ꢁTC2871: More Communication Configurations Using External Connections
28701f
28
LTC2870/LTC2871
TYPICAL APPLICATIONS
VCC = 3V to 5.5V, Vꢁ = 1.7V to VCC. ꢁogic input pins not shown are tied to a valid logic state.
V
L
V
L
LTC2871
LTC2871
RX232
RX232
DX232
DX485
CH2
DX232
DX485
CH2
LB
RX485
H/F
LB
RX485
H/F
TE485
TE485
Y
Z
A
DI
RO
120Ω
120Ω
B
ROUT1
RIN1
DIN1
RXIN
DOUT1
RXOUT
RS485
UP TO 4000 FT
CAT5e CABLE
RS232
RS232
ROUT1
DIN1
RIN1
DRIVER
OUT
DRIVER
IN
ROUT1
Y
Z
A
B
RO
DI
120Ω
120Ω
GND
GND
28701 F42
Figure 42. RS232 Extension Cord Using RS232 to RS485 Conversion
SLAVE
SLAVE
LTC2852
LTC2852
SLAVE
LTC2870/LTC2871
MASTER
LTC2855
120Ω
120Ω
120Ω
V
3.3V
L
TE485
TE
28701 F43
Figure 43. RS485 Full-Duplex Network
28701f
29
LTC2870/LTC2871
TYPICAL APPLICATIONS
LTC2871
LTC2871
DIN1
DOUT1
DIN1
DOUT1
RIN1
PORT 1
LOGIC
INTERFACE
PORT 1
LINE
INTERFACE
PORT 1
LOGIC
INTERFACE
PORT 1
LINE
INTERFACE
ROUT1
RIN1
ROUT1
DIN2
DOUT2
RIN2
DIN2
DOUT2
RIN2
PORT 2A/2B
LOGIC
INTERFACE
PORT 2A
LINE
INTERFACE
PORT 2A
LOGIC
INTERFACE
PORT 2A/2B
LINE
ROUT2
ROUT2
INTERFACE
CH2
CH2
SELECT LINE 2A
SELECT LINE 2B
SELECT LINE 2A
SELECT LINE 2B
LTC2871
LTC2871
CH2
CH2
DIN2
DOUT2
RIN2
DIN2
DOUT2
RIN2
PORT 2B
LINE
INTERFACE
PORT 2B
LOGIC
INTERFACE
ROUT2
ROUT2
DIN1
DOUT1
RIN1
DIN1
DOUT1
RIN1
PORT 3
LOGIC
INTERFACE
PORT 3
LINE
INTERFACE
PORT 3
LOGIC
INTERFACE
PORT 3
LINE
ROUT1
ROUT1
INTERFACE
28701 F44
28701 F45
Figure 44. RS232 Triple Transceiver
with Selectable ꢁine Interface
Figure 45. RS232 Triple Transceiver
with Selectable ꢁogic Interface
LTC2870/
LTC2871
H/F
SELECT
RS485
INTERFACE
INPUT2 INPUT1
Y
Z
INPUT1
INPUT2
RA,
RO
A
B
28701 F46
Figure 4ꢀ. RS485 Receiver with Multiplexed Inputs
28701f
30
LTC2870/LTC2871
TYPICAL APPLICATIONS
3V TO 5.5V
3V TO 5.5V
10μH
220nF
220nF
10μH
2.2μF
2.2μF
1.7V TO V
CC
V
L
SW
LTC2871
CAP
CAP
SW
LTC2870
V
CC
CC
1.7V TO V
CC
V
L
V
H/F
0.1μF
H/F
0.1μF
TE485
TE485
RS485
INTERFACE
485/232
Y
Y
DY
RA
DI
120Ω
120Ω
Z
Z
A
A
RO
120Ω
120Ω
B
B
DIN1
DOUT1
ROUT1
DIN2
RIN1
RS232
INTERFACE
DOUT2
ROUT2
RIN2
GND
V
V
DD
DD
1μF
V
V
1μF
EE
EE
GND
28701 F47
1μF
1μF
Figure 47. Typical Supply Connections with External Components Shown
3V TO 5.5V
470nF
22μH
2.2μF
V
L
SW
CAP
CAP
V
CC
CC
V
V
L
LTC2870/
LTC2871
LTC2870/
LTC2871
SW
GND
V
V
V
V
DD
GND
DD
EE
EE
28701 F48
2.2μF
2.2μF
INDUCTOR: TAIYO YUDEN CBC2518T220M,
MURATA LQH32CN220K53
Figure 48. Running Two ꢁTC2870 or ꢁTC2871 Devices from One Shared Power Source
28701f
31
LTC2870/LTC2871
PACKAGE DESCRIPTION
FE Package
28-ꢁead Plastic TSSOP (4.4mm)
(Reference LTC DWG # 05-08-1663)
Exposed Pad Variation EB
9.60 – 9.80*
(.378 – .386)
4.75
(.187)
4.75
(.187)
28 2726 25 24 23 22 21 20 19 18 1716 15
6.60 ±0.10
2.74
(.108)
EXPOSED
PAD HEAT SINK
ON BOTTOM OF
PACKAGE
4.50 ±0.10
SEE NOTE 4
6.40
(.252)
BSC
2.74
(.108)
0.45 ±0.05
1.05 ±0.10
0.65 BSC
RECOMMENDED SOLDER PAD LAYOUT
5
7
1
2
3
4
6
8
9 10 12 13 14
11
1.20
(.047)
MAX
4.30 – 4.50*
(.169 – .177)
0.25
REF
0° – 8°
0.65
(.0256)
BSC
0.09 – 0.20
(.0035 – .0079)
0.50 – 0.75
(.020 – .030)
0.05 – 0.15
(.002 – .006)
FE28 (EB) TSSOP 0204
0.195 – 0.30
(.0077 – .0118)
TYP
NOTE:
1. CONTROLLING DIMENSION: MILLIMETERS 4. RECOMMENDED MINIMUM PCB METAL SIZE
2. DIMENSIONS ARE IN
FOR EXPOSED PAD ATTACHMENT
MILLIMETERS
(INCHES)
*DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.150mm (.006") PER SIDE
3. DRAWING NOT TO SCALE
28701f
32
LTC2870/LTC2871
PACKAGE DESCRIPTION
FE Package
38-ꢁead Plastic TSSOP (4.4mm)
(Reference LTC DWG # 05-08-1772 Rev A)
Exposed Pad Variation AA
4.75 REF
9.60 – 9.80*
(.378 – .386)
4.75
(.187)
REF
38
20
6.60 0.10
2.74 REF
4.50 REF
SEE NOTE 4
6.40
REF (.252)
BSC
2.74
(.108)
0.315 0.05
1.05 0.10
0.50 BSC
RECOMMENDED SOLDER PAD LAYOUT
1
19
1.20
(.047)
MAX
4.30 – 4.50*
(.169 – .177)
0.25
REF
0o – 8o
0.50
(.0196)
BSC
0.09 – 0.20
(.0035 – .0079)
0.50 – 0.75
(.020 – .030)
0.05 – 0.15
(.002 – .006)
0.17 – 0.27
FE38 (AA) TSSOP 0608 REV A
(.0067 – .0106)
TYP
NOTE:
1. CONTROLLING DIMENSION: MILLIMETERS 4. RECOMMENDED MINIMUM PCB METAL SIZE
2. DIMENSIONS ARE IN
FOR EXPOSED PAD ATTACHMENT
MILLIMETERS
(INCHES)
*DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.150mm (.006") PER SIDE
3. DRAWING NOT TO SCALE
28701f
33
LTC2870/LTC2871
PACKAGE DESCRIPTION
UFD Package
28-ꢁead Plastic QFN (4mm × 5mm)
(Reference LTC DWG # 05-08-1712 Rev B)
0.70 ±0.05
4.50 ± 0.05
3.10 ± 0.05
2.50 REF
2.65 ± 0.05
3.65 ± 0.05
PACKAGE OUTLINE
0.25 ±0.05
0.50 BSC
3.50 REF
4.10 ± 0.05
5.50 ± 0.05
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
PIN 1 NOTCH
R = 0.20 OR 0.35
× 45° CHAMFER
2.50 REF
R = 0.115
TYP
R = 0.05
TYP
0.75 ± 0.05
4.00 ± 0.10
(2 SIDES)
27
28
0.40 ± 0.10
PIN 1
TOP MARK
(NOTE 6)
1
2
5.00 ± 0.10
(2 SIDES)
3.50 REF
3.65 ± 0.10
2.65 ± 0.10
(UFD28) QFN 0506 REV B
0.25 ± 0.05
0.50 BSC
0.200 REF
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO-220 VARIATION (WXXX-X).
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON THE TOP AND BOTTOM OF PACKAGE
28701f
34
LTC2870/LTC2871
PACKAGE DESCRIPTION
UHF Package
38-ꢁead Plastic QFN (5mm × 7mm)
(Reference LTC DWG # 05-08-1701 Rev C)
0.70 p 0.05
5.50 p 0.05
4.10 p 0.05
3.00 REF
5.15 0.05
3.15 0.05
PACKAGE
OUTLINE
0.25 p 0.05
0.50 BSC
5.5 REF
6.10 p 0.05
7.50 p 0.05
RECOMMENDED SOLDER PAD LAYOUT
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
PIN 1 NOTCH
R = 0.30 TYP OR
0.35 s 45o CHAMFER
0.75 p 0.05
3.00 REF
5.00 p 0.10
37
38
0.00 – 0.05
0.40 p0.10
PIN 1
TOP MARK
1
2
(SEE NOTE 6)
5.15 0.10
5.50 REF
7.00 p 0.10
3.15 0.10
(UH) QFN REF C 1107
0.200 REF 0.25 p 0.05
R = 0.125
TYP
R = 0.10
TYP
0.50 BSC
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING CONFORMS TO JEDEC PACKAGE
OUTLINE M0-220 VARIATION WHKD
2. DRAWING NOT TO SCALE
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.20mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON THE TOP AND BOTTOM OF PACKAGE
3. ALL DIMENSIONS ARE IN MILLIMETERS
28701f
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
35
LTC2870/LTC2871
TYPICAL APPLICATION
Quad RS232 Transceiver with RS485 Communication Over Half-Duplex, Terminated Bus
3V TO 5.5V
470nF
22μH
2.2μF
V
L
SW
LTC2871
CAP
CAP
V
V
L
CC
CC
LTC2804
SW
V
T1IN
T1OUT1
TE485
ROUT1
T2IN
RIN1
DIN1
DOUT1
T2OUT
ROUT1
DIN2
RIN1
ROUT2
RIN2
DOUT2
ROUT2
RO
RIN2
A
V
V
GND
EE
DD
3.3V
120Ω
B
V
CC
LTC2854
0.1μF
TE
DI
Y
A
B
DI
120Ω
Z
120Ω
RO
GND
V
V
EE
DD
GND
28701 TA02
2.2μF
2.2μF
RELATED PARTS
PART NUMBER
LTC1334
DESCRIPTION
COMMENTS
Single 5V RS232/RS485 Multiprotocol Transceiver
Single 5V RS232/RS485 Multiprotocol Transceiver
Dual Port, Single 5V Supply, Configurable, 10kV ESD
Single Port, Configurable
LTC1387
LTC2801/LTC2802/ 1.8V to 5.5V RS232 Single and Dual Transceivers
LTC2803/LTC2804
Up to 1Mbps, 10kV ESD, Logic Supply Pin, Tiny DFN Packages
LTC2854/LTC2855 3.3V 20Mbps RS485 Transceiver with Integrated
Switchable Termination
3.3V Supply, Integrated, Switchable, 120Ω Termination Resistor, 25kV ESD
5V Supply, Integrated, Switchable, 120Ω Termination Resistor, 15kV ESD
LTC2859/LTC2861 20Mbps RS485 Transceiver with Integrated
Switchable Termination
LTM2881
Complete Isolated RS485/RS422 μModule
Transceiver + Power
20Mbps, 2500V
Isolation with Integrated DC/DC Converter, Integrated,
RMS
Switchable, 120Ω Termination Resistor, 15kV ESD
LTM2882
Dual Isolated RS232 μModule Transceiver + Power 1Mbps, 2500V
Isolation with Integrated DC/DC Converter, 10kV ESD
RMS
28701f
LT 1210 • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
36
●
●
© LINEAR TECHNOLOGY CORPORATION 2010
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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