LINER LTC2870IFEPBF

LTC2870/LTC2871
RS232/RS485 Multiprotocol
Transceivers with
Integrated Termination
DESCRIPTION
FEATURES
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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
The LTC®2870/LTC2871 are robust pin-configurable multiprotocol 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 inductor 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.
TYPICAL APPLICATIONS
Protocol Switching with
Automatic Termination Selection
1.7V TO VCC
VL
RS232 RS485
3V TO 5.5V
LTC2870
Simultaneous Protocols and
RS485 Termination Switching
1.7V TO VCC
VL
VCC
485/232
RS485
TERMINATION
DY
3V TO 5.5V
LTC2871
RS485 Duplex Switching
1.7V TO VCC
VCC
VL
3V TO 5.5V
LTC2870,
LTC2871
VCC
TE485
Y
OFF ON
120Ω
Y
DI
DI,
Z
Z
DY
A
DZ
RO
A
B
RB
RS485
FULL HALF
DIN1
ROUT1
DIN2
ROUT2
Z
120Ω
B
RA
Y
DOUT1
RIN1
DOUT2
H/F
DUPLEX
RO,
RB
A
B
RIN2
28701 TA01
28701f
1
LTC2870/LTC2871
ABSOLUTE MAXIMUM RATINGS
(Notes 1 and 2)
Input Supplies
VCC, VL..................................................... –0.3V to 7V
Generated Supplies
VDD ................................................ VCC – 0.3V to 7.5V
VEE ......................................................... 0.3V to –7.5V
VDD – VEE..............................................................15V
SW ........................................... –0.3V to (VDD + 0.3V)
CAP............................................. 0.3V to (VEE – 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 (VL + 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
LTC2870
TOP VIEW
GND
VCC
VL
LB
H/F
TE485
TOP VIEW
28 27 26 25 24 23
VEE 1
22 A
RA 2
21 B
RB 3
20 VCC
485/232 4
19 Y
29
VEE
RXEN 5
18 GND
17 Z
DXEN 6
LB
1
28 VL
H/F
2
27 VCC
TE485
3
26 GND
VEE
4
25 A
RA
5
24 B
23 VCC
RB
6
485/232
7
RXEN
8
DXEN
9
29
VEE
22 Y
21 GND
20 Z
DY 7
16 VCC
DY 10
19 VCC
DZ 8
15 VDD
DZ 11
18 VDD
FEN 12
17 SW
GND 13
16 GND
CAP 14
15 VEE
SW
GND
VEE
CAP
FEN
GND
9 10 11 12 13 14
UFD PACKAGE
28-LEAD (4mm s 5mm) PLASTIC QFN
TJMAX = 125°C, θJA = 43°C/W
EXPOSED PAD (PIN 29) IS VEE,
MUST BE SOLDERED TO PCB
FE PACKAGE
28-LEAD PLASTIC TSSOP
TJMAX = 125°C, θJA = 25°C/W
EXPOSED PAD (PIN 29) IS VEE,
MUST BE SOLDERED TO PCB
28701f
2
LTC2870/LTC2871
PIN CONFIGURATIONS
LTC2871
LTC2871
TOP VIEW
VL
1
38 RO
35 RIN1
34 RIN2
VCC
4
RO
TE485
VL
36 GND
38 37 36 35 34 33 32
LB
27 VCC
3
H/F
2
H/F
TE485
LB
GND
TOP VIEW
VEE 1
31 RIN1
VEE
5
ROUT1 2
30 RIN2
ROUT1
6
33 A
ROUT2 3
29 A
ROUT2
7
32 B
CH2 4
28 B
CH2
8
RX485
9
31 VCC
30 Y
RX485 5
27 VCC
DX485 6
26 Y
39
VEE
DI 7
DX485 10
25 GND
DI 11
24 Z
DIN1 8
23 DOUT1
DIN2 9
DX232 10
22 DOUT2
RX232 11
21 VCC
20 VDD
VEE 12
VEE
SW
GND
VEE
CAP
FEN
GND
13 14 15 16 17 18 19
UHF PACKAGE
38-LEAD (5mm s 7mm) PLASTIC QFN
39
VEE
29 GND
28 Z
DIN1 12
27 DOUT1
DIN2 13
26 DOUT2
DX232 14
25 VCC
RX232 15
VEE 16
24 VDD
23 VEE
FEN 17
22 SW
GND 18
21 GND
CAP 19
20 VEE
FE PACKAGE
38-LEAD PLASTIC SSOP
TJMAX = 125°C, θJA = 29°C/W
EXPOSED PAD (PIN 39) IS VEE,
MUST BE SOLDERED TO PCB
TJMAX = 125°C, θJA = 34°C/W
EXPOSED PAD (PIN 39) IS VEE,
MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
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
CONFIGURABLE TRANSCEIVER COMBINATIONS (RS485 + RS232)
PACKAGES
LTC2870
(0 + 0), (1 + 0), (0 + 2)
28-Lead QFN, 28-Lead TSSOP
LTC2871
(0 + 0), (1 + 0), (1 + 1), (1 + 2), (0 + 1), (0 + 2)
38-Lead QFN, 38-Lead TSSOP
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 = VL = 3.3V, TE485 = 0V, LB = 0V unless otherwise noted.
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Power Supply
VCC
Supply Voltage Operating Range
VL
Logic Supply Voltage Operating Range
VL ≤ VCC
VCC Supply Current in Shutdown Mode
RXEN = VL, DXEN = TE485 = FEN = 0V, (LTC2870)
DX485 = DX232 = TE485 = FEN = H/F = 0V,
RX485 = RX232 = VL (LTC2871)
VCC Supply Current in Transceiver Mode
(Outputs Unloaded) (Note 3)
485/232 = DXEN = VL, RXEN = 0V,
DY/DZ = 0V or VL (LTC2870)
DX485 = DX232 = VL, RX485 = RX232 = 0V,
DI/DIN1/DIN2 = 0V or VL (LTC2871)
VL Supply Current in Transceiver Mode
(Outputs Unloaded)
3
5.5
V
1.7
VCC
V
60
μA
l
8
3.3
l
0
mA
5
μA
6
VCC
VCC
V
V
V
RS485 Driver
|VOD|
Differential Output Voltage
RL = ∞, VCC = 3V (Figure 1)
RL = 27Ω, VCC = 3V (Figure 1)
RL = 50Ω, VCC = 3.13V (Figure 1)
l
l
l
Δ|VOD|
Difference in Magnitude of Differential Output
Voltage for Complementary Output States
RL = 27Ω, VCC = 3V (Figure 1)
RL = 50Ω, VCC = 3.13V (Figure 1)
l
l
0.2
0.2
V
V
VOC
Common Mode Output Voltage
RL = 27Ω or 50Ω (Figure 1)
l
3
V
Δ|VOC|
Difference in Magnitude of Common Mode
Output Voltage for Complementary Output
States
RL = 27Ω or 50Ω (Figure 1)
l
0.2
V
IOZD485
Three-State (High Impedance) Output Current
VOUT = 12V or –7V, VCC = 0V or 3.3V (Figure 2)
l
–100
125
μA
–7V ≤ VOUT ≤ 12V (Figure 2)
l
–250
250
mA
125
μA
IOSD485
Maximum Short-Circuit Current
1.5
1.5
2
RS485 Receiver
IIN485
Input Current
VIN = 12V or –7V, VCC = 0V or 3.3V (Figure 3)
(Note 5)
l
–100
RIN485
Input Resistance
VIN = 12V or –7V, VCC = 0V or 3.3V (Figure 3)
(Note 5)
l
96
Differential Input Signal Threshold Voltage
(A-B)
–7V ≤ (A or B) ≤ 12V (Note 5)
l
Input Hysteresis
B = 0V (Notes 3, 5)
Differential Input Failsafe Threshold Voltage
–7V ≤ (A or B) ≤ 12V (Note 5)
Input DC Failsafe Hysteresis
B = 0V (Note 5)
Output Low Voltage
Output Low, I(RA, RO) = 3mA (Sinking),
3V ≤ VL ≤ 5.5V
l
0.4
V
Output Low, I(RA, RO) = 1mA (Sinking),
1.7V ≤ VL < 3V
l
0.4
V
Output High, I(RA, RO) = –3mA (Sourcing),
3V ≤ VL ≤ 5.5V
l
VL – 0.4
V
Output High, I(RA, RO) = –1mA (Sourcing),
1.7V ≤ VL < 3V
l
VL – 0.4
V
Three-State (High Impedance) Output Current
0V ≤ (RA, RO), ≤VL, VL = 5.5V
l
Short-Circuit Output Current
0V ≤ (RA, RO), ≤VL, VL = 5.5V
l
VOL
VOH
Output High Voltage
125
kΩ
±200
mV
0
mV
130
l
–200
–50
mV
25
0
mV
±5
μA
±125
mA
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 = VL = 3.3V, TE485 = 0V, LB = 0V unless otherwise noted.
SYMBOL PARAMETER
RTERM
Terminating Resistor
CONDITIONS
MIN
TYP
MAX
UNITS
TE485 = VL, A – B = 2V, B = –7V, 0V, 10V
(Figure 8) (Note 5)
l
108
120
156
Ω
RS232 Driver
VOLD
Output Low Voltage
RL = 3kΩ; VEE ≤ –5.9V
l
–5
–5.7
–7.5
V
VOHD
Output High Voltage
RL = 3kΩ; VDD ≥ 6.5V
l
5
6.2
7.5
V
Three-State (High Impedance) Output Current
Y or Z (LTC2870) = ±15V
RS232 Receiver Enabled
DOUT1 or DOUT2 (LTC2871) = ±15V
l
±156
μA
l
±10
μA
Driver Output = 0V
l
±35
±90
mA
Output Short-Circuit Current
RS232 Receiver
Input Threshold Voltage
l
0.6
1.5
2.5
V
Input Hysteresis
l
0.1
0.4
1.0
V
0.4
V
Output Low Voltage
I(RA, RB, ROUT1, ROUT2) = 1mA (Sinking)
1.7V ≤ VL ≤ 5.5V
l
Output High Voltage
I(RA, RB, ROUT1, ROUT2) = –1mA (Sourcing)
1.7V ≤ VL ≤ 5.5V
l
VL – 0.4
Input Resistance
–15V ≤ (A, B, RIN1, RIN2) ≤ 15V,
RS232 Receiver Enabled
l
3
Three-State (High Impedance) Output Current
0V ≤ (RA, RB, ROUT1, ROUT2) ≤ VL
Output Short-Circuit Current
VL = 5.5V
0V ≤ (RA, RB, ROUT1, ROUT2) ≤ VL
V
5
7
kΩ
l
0
±5
μA
l
±25
±50
mA
Logic Inputs
Threshold Voltage
l
Input Current
l
0.4
0
0.75 • VL
V
±5
μA
Power Supply Generator
VDD
Regulated VDD Output Voltage
VEE
Regulated VEE Output Voltage
RS232 Drivers Enabled, Outputs Loaded with
RL = 3kΩ to GND, DIN1/DY = VL, DIN2/DZ = 0V
(Note 3)
7
V
–6.3
V
Human Body Model to GND or VCC, Powered or
Unpowered (Note 7)
±26
kV
±16
kV
Human Body Model (Note 7)
±4
kV
ESD
LTC2870 Interface Pins (A, B, Y, Z)
LTC2871 Interface Pins (A, B, Y, Z, RIN1, RIN2,
DOUT1, DOUT2)
All Other Pins
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 = VL = 3.3V, TE485 = 0V, LB = 0V unless otherwise noted. VL ≤ VCC.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
RS485 AC Characteristics
Maximum Data Rate
(Note 3)
l
Driver Propagation Delay
RDIFF = 54Ω, CL = 100pF (Figure 4)
l
20
70
ns
Driver Propagation Delay Difference
|tPLHD485 – tPHLD485|
RDIFF = 54Ω, CL = 100pF (Figure 4)
l
1
6
ns
tSKEWD485
Driver Skew (Y to Z)
RDIFF = 54Ω, CL = 100pF (Figure 4)
l
1
±6
ns
tRD485, tFD485
Driver Rise or Fall Time
RDIFF = 54Ω, CL = 100pF (Figure 4)
l
15
ns
tZLD485, tZHD485,
tLZD485, tHZD485
Driver Output Enable or Disable Time
FEN = VL, RL = 500Ω, CL = 50pF (Figure 5)
l
120
ns
tZHSD485, tZLSD485 Driver Enable from Shutdown
RL = 500Ω, CL = 50pF (Figure 5)
l
8
μs
tPLHR485, tPHLR485 Receiver Input to Output
CL = 15pF, VCM = 1.5V, |A – B| = 1.5V
(Figure 6) (Note 5)
l
65
85
ns
tPLHD485
tPHLD485
20
Mbps
tSKEWR485
Differential Receiver Skew
|tPLHR485 – tPHLR485|
CL = 15pF (Figure 6)
l
1
6
ns
tRR485, tFR485
Receiver Output Rise or Fall Time
CL = 15pF (Figure 6)
l
3
15
ns
tZLR485, tZHR485,
tLZR485, tHZR485
Receiver Output Enable or Disable Time
FEN = VL, RL = 1kΩ, CL = 15pF (Figure 7)
l
50
ns
tRTEN485, tRTZ485
Termination Enable or Disable Time
FEN = VL, VB = 0V, VAB = 2V (Figure 8) (Note 5)
l
100
μs
Maximum Data Rate
RL = 3kΩ, CL = 2500pF
RL = 3kΩ, CL = 500pF
(Note 3)
l
l
100
500
Driver Slew Rate (Figure 9)
RL = 3kΩ, CL = 2500pF
RL = 3kΩ, CL = 50pF
l
l
4
RL = 3kΩ, CL = 50pF (Figure 9)
l
RS232 AC Characteristics
tPHLD232, tPLHD232 Driver Propagation Delay
kbps
kbps
1
30
V/μs
V/μs
2
μs
tSKEWD232
Driver Skew
RL = 3kΩ, CL = 50pF (Figure 9)
tZLD232, tZHD232,
tLZD232, tHZD232
Driver Output Enable or Disable Time
FEN = VL, RL = 3kΩ, CL = 50pF (Figure 10)
l
0.4
2
μs
CL = 150pF (Figure 11)
l
60
200
ns
tPHLR232, tPLHR232 Receiver Propagation Delay
50
ns
tSKEWR232
Receiver Skew
CL = 150pF (Figure 11)
tRR232, tFR232
Receiver Rise or Fall Time
CL = 150pF (Figure 11)
l
60
200
ns
FEN = VL, RL = 1kΩ, CL = 150pF (Figure 12)
l
0.7
2
μs
FEN =
l
0.2
2
ms
tZLR232, tZHR232,
tLZR232, tHZR232
Receiver Output Enable or Disable Time
25
ns
Power Supply Generator
VDD /VEE Supply Rise Time
, (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 3: Guaranteed by other measured parameters and not tested directly.
Note 4: Time from FEN until VDD ≥ 5V and VEE ≤ –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 = VL.
Note 6: This IC includes overtemperature protection that is intended
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 7: Guaranteed by design and not subject to production test.
28701f
6
LTC2870/LTC2871
TYPICAL PERFORMANCE CHARACTERISTICS
VCC Supply Current vs Supply
Voltage in Shutdown Mode
TA = 25°C, VCC = VL = 3.3V, unless otherwise noted.
VCC Supply Current vs Supply
Voltage in Fast Enable Mode
30
5
VCC Supply Current
vs RS485 Data Rate
100
ALL DRIVERS AND RECEIVERS DISABLED
TE485 LOW
80
H/F HIGH
20
15
H/F LOW
10
4
SUPPLY CURRENT (mA)
SUPPLY CURRENT (mA)
INPUT CURRENET (μA)
25
85°C
3
25°C
–40°C
2
VCC = 5V
VCC = 3.3V
ALL RS485 DRIVERS
AND RECEIVERS
SWITCHING.
CL = 100pF ON EACH
DRIVER OUTPUT.
60
TE HIGH
40
20
5
TE LOW
0
3.5
3
4.5
4
INPUT VOLTAGE (V)
5
1
5.5
3
3.5
4
4.5
SUPPLY VOLTAGE (V)
20
2.5nF
0.5nF
15
0.05nF
4.5
ALL DRIVERS AND
RECEIVERS SWITCHING.
DRIVER OUTPUTS TIED TO
RECEIVER INPUTS.
RS232: 0.5Mbps (CL = 500pF)
RS485: 20Mbps (CL = 100pF)
TE485 HIGH
110
0.5nF
2.5nF
25
120
VCC = 5V
VCC = 3.3V
RS485 Driver Differential Output
Voltage vs Temperature
100
3.5
90
–40°C
0
100
200
300
DATA RATE (kbps)
70
3
3.5
4
4.5
SUPPLY VOLTAGE (V)
5
VCC = 3.3V, VL = 1.7V
VCC = 5V, VL = 1.7V
VCC = 3.3V, VL = 3.3V
VCC = 5V, VL = 5V
3.0
150
2.5
100
SKEW (ns)
DELAY (ns)
1.5
1.0
0.5
–25
50
0
25
TEMPERATURE (°C)
75
100
28701 G06
0
25
50
TEMPERATURE (°C)
0
–50
–25
0
25
50
TEMPERATURE (°C)
100
75
RS485 Driver Short-Circuit
Current vs Short-Circuit Voltage
2.0
10
–25
28701 G06
SHORT-CIRCUIT CURRENT (mA)
50
0
–50
0
–50
5.5
RS485 Driver Skew
vs Temperature
20
VCC = 5V
VCC = 3.3V
28701 G05
RS485 Driver Propagation Delay
vs Temperature
30
RL = 54Ω
1.0
28701 G04
40
2.0
0.5
500
400
RL = 100Ω
2.5
85°C
0.05nF
5
RL = 54Ω
3.0
1.5
25°C
80
10
RL = 100Ω
4.0
VOLTAGE (V)
INPUT CURRENT (mA)
30
100
28701 G03
VCC Supply Current vs Supply
Voltage, All Transceivers at Max
Rate (LTC2871)
SUPPLY CURRENT (mA)
ALL RS232 DRIVERS
AND RECEIVERS
SWITCHING.
1
10
DATA RATE (Mbps)
28701 G02
VCC Supply Current
vs RS232 Data Rate
35
5.5
5
28701 G01
0
0.1
75
100
28701 G08
50
VCC = 5V
VCC = 3.3V
OUTPUT LOW
0
–50
OUTPUT HIGH
–100
–150
–10
0
5
–5
10
SHORT-CIRCUIT VOLTAGE (V)
15
28701 G09
28701f
7
LTC2870/LTC2871
TYPICAL PERFORMANCE CHARACTERISTICS
RS485 Receiver Propagation
Delay vs Temperature
RS485 Receiver Skew
vs Temperature
VCC = 3.3V, VL = 1.7V
VCC = 5V, VL = 1.7V
VCC = 3.3V, VL = 3.3V
VCC = 5V, VL = 5V
70
RS485 Receiver Output Voltage
vs Load Current
3.0
6
2.5
5
OUTPUT VOLTAGE (V)
80
TA = 25°C, VCC = VL = 3.3V, unless otherwise noted.
SKEW (ns)
DELAY (ns)
2.0
60
1.5
1.0
50
0.5
40
–50
0
25
50
TEMPERATURE (°C)
–25
0
25
50
TEMPERATURE (°C)
–25
6
INPUT LOW
1.2
4
3
2
0
25
50
TEMPERATURE (°C)
75
0
2
4
6
8
OUTPUT CURRENT (mA)
126
124
122
120
118
116
10
110
–50
RS232 Operation at 500kbps
DIN1
5V/DIV
DI
485/232
Y
1V/DIV
5V/DIV
Y
5V/DIV
100
75
LTC2870 Drivers Changing Modes
Z
DOUT2
ROUT1
0
25
50
TEMPERATURE (°C)
28701 G15
RS485 Operation at 20Mbps
DOUT1
–25
28701 G14
28701 G13
5V/DIV
VCM = –7V
VCM = 2V
VCM = 12V
128
112
0
100
DIN2
10
114
1
VCC = 5V
VCC = 3.3V
4
6
8
OUTPUT CURRENT (mA)
130
RESISTANCE (Ω)
OUTPUT VOLTAGE (V)
THRESHOLD VOLTAGE (V)
1.6
2
RS485 Termination Resistance
vs Temperature
VL = 5V
VL = 3.3V
VL = 1.7V
5
1.8
INPUT HIGH
0
28701 G12
RS232 Receiver Output Voltage
vs Load Current
2.0
–25
2
28701 G11
RS232 Receiver Input Threshold
vs Temperature
1.0
–50
3
0
100
75
28701 G10
1.4
4
1
0
–50
100
75
VL = 5V
VL = 3.3V
VL = 1.7V
Z
RS232
MODE
RO
RS485
MODE
RS232
MODE
ROUT2
1μs/DIV
WRAPPING DATA
DOUT LOADS: 5kΩ + 50pF
28701 G16
20ns/DIV
H/F HIGH
Y, Z LOADS: 120Ω (DIFF) + 50pF
28701 G17
2μs/DIV
28701 G18
28701f
8
LTC2870/LTC2871
TYPICAL PERFORMANCE CHARACTERISTICS
RS232 Driver Outputs Enabling
and Disabling
TA = 25°C, VCC = VL = 3.3V, unless otherwise noted.
VDD and VEE Powering Up
VDD and VEE Ripple
VDD RIPPLE
DX232
2V/DIV
DOUT1
FEN
FEN = 1
10mV/DIV
DOUT2
5V/DIV
VEE RIPPLE
VDD
DOUT1
5V/DIV
FEN = 0
DOUT2
40μs/DIV
VEE
28701 G19
40μs/DIV
28701 G20
TOP CURVES: FAST ENABLE j DX232
BOTTOM CURVES: SHUTDOWN j DX232
28701 G21
40μs/DIV
FAST ENABLE MODE,
ALL DRIVERS AND RECEIVERS DISABLED.
PIN FUNCTIONS
PIN NAME
LTC2870
QFN
LTC2870
TSSOP
LTC2871
QFN
LTC2871
TSSOP DESCRIPTION
VCC
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 VCC (adjacent to VDD) and GND.
VL
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 VCC. Keep VL ≤ VCC for
proper operation. However, VL > VCC will not damage the device, provided that absolute
maximum limits are respected.
VDD
15
18
20
24
Generated Positive Supply Voltage for RS232 Driver (+7V). Connect 1μF capacitor
between VDD and GND.
VEE
1, 12, 29
4, 15, 29
1, 12, 16,
19, 39
GND
10, 13,
18, 23
13, 16,
21, 26
14, 17,
25, 32
18, 21,
29, 36
CAP
11
14
15
19
Charge Pump Capacitor for Generated Negative Supply Voltage. Connect a 220nF
capacitor between CAP and SW.
SW
14
17
18
22
Switch Pin. Connect 10μH inductor between SW and VCC.
A
22
25
29
33
RS485 Positive Receiver Input (Full-Duplex Mode) or RS232 Receiver Input 1 (LTC2870).
B
21
24
28
32
RS485 Negative Receiver Input (Full-Duplex Mode) or RS232 Receiver Input 2 (LTC2870).
RA
2
5
RS485 Differential Receiver Output or RS232 Receiver Output 1.
RB
3
6
RS232 Receiver Output 2.
5, 16, 20, Generated Negative Supply Voltage for RS232 Driver (–6.3V). Tie all pins together and
23, 39 connect 1μF capacitor between VEE (adjacent to the CAP pin) and GND.
Ground. Tie all four pins together.
RO
34
38
RS485 Differential Receiver Output.
RIN1
31
35
RS232 Receiver Input 1.
RIN2
30
34
RS232 Receiver Input 2.
ROUT1
2
6
RS232 Receiver Output 1.
ROUT2
3
7
RS232 Receiver Output 2.
DIN1
8
12
RS232 Driver Input 1.
DIN2
9
13
RS232 Driver Input 2.
28701f
9
LTC2870/LTC2871
PIN FUNCTIONS
PIN NAME
LTC2870
QFN
LTC2870
TSSOP
LTC2871
QFN
LTC2871
TSSOP DESCRIPTION
DOUT1
23
27
RS232 Driver Output 1.
DOUT2
22
26
RS232 Driver Output 2.
DI
7
11
RS485 Driver Input.
DY
7
10
RS485 Driver Input or RS232 Driver Input 1.
DZ
8
11
RS232 Driver Input 2.
Y
19
22
26
30
RS485 Positive Driver Output. RS232 Driver Output 1 (LTC2870).
RS485 Positive Receiver Input (LTC2870 or LTC2871 in Half-Duplex Mode).
Z
17
20
24
28
RS485 Negative Driver Output or RS232 Driver Output 2 (LTC2870).
RS485 Negative Receiver Input (LTC2870 or LTC2871 in Half-Duplex Mode).
485/232
4
7
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
5
8
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 .
DXEN
6
9
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.
RX232
11
15
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.
RX485
5
9
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
10
14
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.
DX485
6
10
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.
H/F
27
2
37
3
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
28
3
38
4
RS485 Termination Enable. A logic high enables a 120Ω 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.
FEN
9
12
13
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
2
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.
4
8
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.
CH2
28701f
10
LTC2870/LTC2871
BLOCK DIAGRAM
LTC2870
1.7V TO 5.5V
(≤ VCC)
3V TO 5.5V
10μH
0.1μF
220nF
2.2μF
VL
VCC
SW
CAP
DXEN
VDD
RXEN
VEE
TE485
RT232
CONTROL
LOGIC
H/F
RT485
485/232
PULSE-SKIPPING
BOOST
REGULATOR
f = 1.2MHz
1μF
1μF
FEN
DRIVERS
LB
232
DY
Y
RT485
485
120Ω
Z
232
DZ
LOOPBACK
PATH
125k
125k
H/F
RECEIVERS
RT232
232
5k
A
125k
RA
RT485
485
5k
125k
120Ω
B
RB
232
GND
2870 BD
28701f
11
LTC2870/LTC2871
BLOCK DIAGRAM
LTC2871
1.7V TO 5.5V
(≤ VCC)
3V TO 5.5V
220nF
10μH
2.2μF
0.1μF
VL
VCC
SW
CAP
DX232
DX485
VDD
RX232
RX485
RT232
CONTROL
LOGIC
TE485
RT485
H/F
VEE
PULSE-SKIPPING
BOOST
REGULATOR
f = 1.2MHz
CH2
1μF
1μF
FEN
DRIVERS
LB
232
DIN1
DOUT1
Y
RT485
DI
485
120Ω
Z
DOUT2
232
DIN2
LOOPBACK
PATH
125k
125k
H/F
RECEIVERS
RT232
ROUT1
232
RIN1
5k
A
125k
RO
RT485
485
120Ω
5k
ROUT2
125k
B
RIN2
232
GND
2871 BD
28701f
12
LTC2870/LTC2871
TEST CIRCUITS
Y OR Z
Y
GND
OR
VL
DY/DI
+
RL
GND
DY/DI
OR
VL
VOD
DRIVER
Z
–
RL
+
IOZD485, IOSD485
DRIVER
+
–
Z OR Y
VOUT
VOC
–
28701 F02
28701 F01
Figure 1. RS485 Driver DC Characteristics
Figure 2. RS485 Driver Output Current
IIN485
+
–
VIN
RIN485 =
A OR B
B OR A
RECEIVER
VIN
IIN485
28701 F03
Figure 3. RS485 Receiver Input Current and Resistance (Note 5)
tPLHD485
DY/DI
Y
DY/DI
RDIFF
Z
0V
tSKEWD485
CL
DRIVER
VL
tPLHD485
Y, Z
VOD
½VOD
CL
Y-Z
90%
10%
0V
0V
tRD485
90%
10%
tFD485
28701 F04
Figure 4. RS485 Driver Timing Measurement
28701f
13
LTC2870/LTC2871
TEST CIRCUITS
RL
Y
VL
DY/DI
OR
GND
GND
OR
VCC
DXEN/
DX485
VL
½VL
½VL
tZLD485,
tZLSD485
CL
½VCC
Y OR Z
DRIVER
0V
tLZD485
VCC
0.5V
VOL
Z
RL
DXEN/DX485
VCC
OR
GND
½VCC
Z OR Y
0V
tHZD485
tZHD485,
tZHSD485
CL
VOH
0.5V
28701 F05
Figure 5. RS485 Driver Enable and Disable Timing Measurements
VAB
±VAB/2
A-B
A
VCM
RECEIVER
0V
tPLHR485
RA/RO
B
CL
±VAB/2
RA/RO
tPHLR485
90%
10%
VL
90%
½VL
½VL
tRR485
–VAB
10%
tFR485
tSKEWR485 = tPLHR485 – tPHLR485
0V
28701 F06
Figure 6. RS485 Receiver Propagation Delay Measurements (Note 5)
RXEN/
RX485
0V TO 3V
VL
½VL
½VL
tZLR485
B
0V
tLZR485
A
RECEIVER
RA/RO
3V TO 0V
RL
VL
OR
GND
½VL
RA/RO
0.5V
CL
RXEN/RX485
0.5V
½VL
RA/RO
tZHR485
VL
tHZR485
VOL
VOH
0V
28701 F07
Figure 7. RS485 Receiver Enable and Disable Timing Measurements (Note 5)
28701f
14
LTC2870/LTC2871
TEST CIRCUITS
IA
A
RECEIVER
TE485
RTERM =
VAB
VL
IA
TE485
+
–
½VL
½VL
0V
VAB
tRTEN485
B
90%
IA
+
–
tRTZ485
10%
VB
28701 F08
Figure 8. RS485 Termination Resistance and Timing Measurements (Note 5)
DRIVER
INPUT
DRIVER
OUTPUT
DRIVER
INPUT
tPHLD232
½VL
tPLHD232
tF
RL
CL
3V
DRIVER
INPUT
–3V
SLEW RATE =
VL
½VL
0V
tR
0V
6V
0V
3V
–3V
VOHD
VOLD
tSKEWD232 = |tPHLD232 – tPLHD232|
tF OR tR
28701 F09
Figure 9. RS232 Driver Timing and Slew Rate Measurements
DRIVER
OUTPUT
0V OR VL
DXEN/DX232
RL
DXEN/
DX232
VL
½VL
½VL
0V
tZHD232
CL
DRIVER
OUTPUT
tHZD232
tZLD232
DRIVER
OUTPUT
0.5V
5V
0V
tLZD232
5V
VOHD
0V
0.5V
VOLD
28701 F10
Figure 10. RS232 Driver Enable and Disable Times
28701f
15
LTC2870/LTC2871
TEST CIRCUITS
RECEIVER
OUTPUT
RECEIVER
INPUT
RECEIVER
INPUT
+3V
1.5V
1.5V
tPHLR232
CL
RECEIVER
OUTPUT
90%
10%
–3V
tPLHR232
½VL
½VL
VL
90%
10%
tRR232
tFR232
tSKEWR232 = |tPLHR232 – tPHLR232|
0V
28701 F11
Figure 11. RS232 Receiver Timing Measurements
RECEIVER
OUTPUT
RL
–3V OR +3V
RXEN/RX232
GND
OR VL
RXEN/
RX232
VL
½VL
½VL
0V
tHZR232
tZHR232
CL
RECEIVER
OUTPUT
tZLR232
RECEIVER
OUTPUT
0.5V
½VL
0V
tLZR232
½VL
VOHR
VL
0.5V
VOLR
28701 F12
Figure 12. RS232 Receiver Enable and Disable Times
28701f
16
LTC2870/LTC2871
FUNCTION TABLES
Table 1. LTC2870 Mode Selection Table
TE485
H/F
LB
DC/DC
CONVERTER MODE AND COMMENTS
0
0
X
X
OFF
Low Power Shutdown: All Main Functions Off
0
X
X
X
OFF
Low Power Shutdown: All Main Functions Off
1
0
0
X
X
ON
Fast-Enable: DC/DC Converter On Only
X
1
X
X
0
ON
RS232 Drivers On
0
0
X
X
X
0
ON
RS232 Receivers On
1
X
1
X
X
0
ON
RS485 Driver On
X
1
0
X
X
X
0
ON
RS485 Receiver On
X
1
X
X
1
X
X
ON
RS485 Driver and Receiver 120Ω Termination Enabled
X
1
X
X
X
0
0
X
RS485 Full-Duplex Mode
X
1
X
X
X
1
0
X
RS485 Half-Duplex Mode
X
1
0
X
X
X
1
ON
RS485 Loopback Mode
X
0
0
X
X
X
1
ON
RS232 Loopback Mode
FEN
485/232
RXEN
DXEN
0
X
1
0
0
1
1
X
X
0
X
X
Table 2. LTC2871 Mode Selection Table (CH2 = 0)
FEN
RX232
DX232
RX485
DX485
TE485
H/F
LB
DC/DC
CONVERTER MODE AND COMMENTS
0
1
0
1
0
0
X
X
OFF
Low Power Shutdown: All Main Functions Off
1
1
0
1
0
0
X
X
ON
Fast-Enable: DC/DC Converter On Only
X
X
1
X
X
X
X
0
ON
RS232 Drivers On
X
0
X
X
X
X
X
0
ON
RS232 Receivers On
X
X
X
X
1
X
X
0
ON
RS485 Driver On
X
X
X
0
X
X
X
0
ON
RS485 Receiver On
X
X
X
X
X
X
0
0
X
RS485 Full-Duplex Mode
X
X
X
X
X
X
1
0
X
RS485 Half-Duplex Mode
X
X
X
0
X
X
X
1
ON
RS485 Loopback Mode
X
0
X
X
X
X
X
1
ON
RS232 Loopback Mode
Table 3. RS232 Receiver Mode (485/232 = 0 for LTC2870, CH2 = 0 for LTC2871)
RX232 OR RXEN
RECEIVER INPUTS
(A, B, RIN1, RIN2)
CONDITIONS
RECEIVER OUTPUTS
(RA, RB, ROUT1, ROUT2)
LTC2870 RECEIVER INPUTS LTC2871 RECEIVER INPUTS
(A, B)
(RIN1, RIN2)
1
X
No Fault
Hi-Z
125kΩ
Hi-Z
0
0
No Fault
1
5kΩ
5kΩ
0
1
No Fault
0
5kΩ
5kΩ
0
X
Thermal Fault
Hi-Z
5kΩ
5kΩ
Table 4. RS232 Driver Mode (485/232 = 0 for LTC2870, CH2 = 0 for LTC2871)
DX232 OR DXEN
DRIVER INPUTS
(DY, DZ, DIN1, DIN2)
CONDITIONS
LTC2870 DRIVER OUTPUTS
(Y, Z)
LTC2871 DRIVER OUTPUTS
(DOUT1, DOUT2)
0
X
No Fault
125kΩ
Hi-Z
1
0
No Fault
1
1
1
1
No Fault
0
0
X
X
Thermal Fault
125kΩ
Hi-Z
28701f
17
LTC2870/LTC2871
FUNCTION TABLES
Table 5. LTC2871 CH2 CONTROL
RS232 RECEIVER INPUTS
RS232 DRIVER OUTPUTS
CH2
DX232
RX232
RIN1
RIN2
DOUT1
DOUT2
X
0
1
Hi-Z
Hi-Z
Hi-Z
Hi-Z
Both Drivers and Receivers Disabled
0
0
0
5kΩ
5kΩ
Hi-Z
Hi-Z
Both Receivers Enabled, Both Drivers Disabled
0
1
1
Hi-Z
Hi-Z
Driven
Driven
Both Receivers Disabled, Both Drivers Enabled
0
1
0
5kΩ
5kΩ
Driven
Driven
1
0
0
5kΩ
Hi-Z
Hi-Z
Hi-Z
Channel 2 Drivers and Receivers Disabled
1
1
1
Hi-Z
Hi-Z
Driven
Hi-Z
Channel 2 Drivers and Receivers Disabled
1
1
0
5kΩ
Hi-Z
Driven
Hi-Z
Channel 2 Drivers and Receivers Disabled
COMMENTS
Both Receivers and Drivers Enabled
Table 6. RS485 Driver Mode (TE485 = 0)
DX485 OR DXEN
DI
CONDITIONS
Y
Z
0
X
No Fault
125kΩ
125kΩ
1
0
No Fault
0
1
1
1
No Fault
1
0
X
X
Thermal Fault
125kΩ
125kΩ
Table 7. RS485 Receiver Mode (LB = 0)
RXEN OR RX485
A - B (NOTE 5)
CONDITIONS
RA, RO
1
X
No Fault
Hi-Z
0
< –200mV
No Fault
0
0
> 200mV
No Fault
1
0
Inputs Open or Shorted Together (DC)
Failsafe
1
X
X
Thermal Fault
Hi-Z
Table 8. RS485 Termination (485/232 = 1 for LTC2870)
TE485
H/F, LB
CONDITIONS
R (A TO B)
R (Y TO Z)
0
X
No Fault
Hi-Z
Hi-Z
1
X
No Fault
120Ω
120Ω
X
X
Thermal Fault
Hi-Z
Hi-Z
Table 9. RS485 Duplex Control (485/232 = 1 for LTC2870)
H/F
RS485 DRIVER OUTPUTS
RS485 RECEIVER INPUTS
0
Y, Z
A, B
1
Y, Z
Y, Z
Table 10. LTC2870 Loopback Functions
Table 11. LTC2871 Loopback Functions
LB
RXEN
MODE
LB
RX232
RX485
MODE
0
X
Not Loopback
0
X
X
Not Loopback
X
1
Not Loopback
X
1
1
Not Loopback
1
0
Loopback (RA = DY, RB = DZ)
1
0
1
Loopback RS232 (ROUT1 = DIN1, ROUT2 = DIN2)
1
1
0
Loopback RS485 (R0 = DI)
1
0
0
Loopback All (ROUT1 = DIN1, ROUT2 = DIN2, RO = DI)
28701f
18
LTC2870/LTC2871
APPLICATIONS INFORMATION
Overview
The LTC2870 and LTC2871 are flexible multiprotocol transceivers 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. Automatically selected integrated termination resistors for both
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.
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 LTC2871 separates the RS232 and RS485 transceivers
into independent I/Os allowing simultaneous operation
of two RS232 transceivers and one RS485 transceiver.
Independent control over driver and receiver mode for
each protocol is provided with logic inputs DX232, RX232,
DX485, RX485. Single channel RS232 operation is possible
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.
Both parts feature rugged operation with ESD ratings
of ±26kV (LTC2870) and ±16kV (LTC2871) HBM on the
RS232 and RS485 receiver inputs and driver outputs, both
unpowered and powered. All other pins offer protection
exceeding ±4kV.
DC/DC Converter
The on-chip DC/DC converter operates from the VCC input,
generating a 7V VDD supply and a charge pumped –6.3V
VEE supply, as shown in Figure 13. VDD and VEE power
the output stage of the RS232 drivers and are regulated
to levels that guarantee greater than ±5V output swing.
C1
220nF
L1
10μH
3V TO 5.5V
C4
2.2μF
SW
VCC
CAP
VDD
C2
1μF
PULSE-SKIPPING
BOOST
REGULATOR
f = 1.2MHz
VEE
28701 F13
C3
1μF
Figure 13. DC/DC Converter
The DC/DC converter requires a 10μH inductor (L1) and a
bypass capacitor (C4) of 2.2μF. The charge pump capacitor
(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 Applications section.
Inductor Selection
A 10μH inductor with a saturation current (ISAT) rating
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
PART NUMBER
MAX
ISAT
(mA) DCR (Ω)
LBC2016T100K
CBC2016T100M
245
380
FSLB2520-100K
220
SIZE(mm)
MANUFACTURER
1.07
1.07
2 × 1.6 × 1.6
2 × 1.6 × 1.6
Taiyo Yuden
www.t-yuden.com
1.1
2.5 × 2 × 1.6
Toko
www.tokoam.com
Capacitor Selection
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.
28701f
19
LTC2870/LTC2871
APPLICATIONS INFORMATION
Inrush Current and Supply Overshoot Precaution
VL Logic Supply and Logic Pins
In certain applications fast supply slew rates are generated
when power is connected. If the VCC voltage is greater
than 4.5V and its rise time is faster than 10μs, the pins
VDD and SW can exceed their absolute maximum values
during start-up. When supply voltage is applied to VCC, the
voltage difference between VCC and VDD generates inrush
current flowing through inductor L1 and capacitors C1 and
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 10μs.
A separate logic supply pin VL allows the LTC2870 and
LTC2871 to interface with any logic signal from 1.7V to
5.5V. All logic I/Os use VL as their high supply. For proper
operation, VL should not be greater than VCC. During
power-up, if VL is higher than VCC, the device will not be
damaged, but behavior of the device is not guaranteed.
If VL is not connected to VCC, bypass VL with a 0.1μF
capacitor to GND.
Although all logic input pins reference VL as their high
supply, they can be driven up to 7V, independent of VL and
VCC, with the exception of FEN, which must not exceed VL
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.
5V
0V
≤10μs
R1
1Ω
1/8W
C4
2.2μF
L1
10μH
C1
220nF
INRUSH
CURRENT
SW
RS232 and RS485 driver outputs are undriven and the
RS485 termination resistors are disabled when VL or VCC
is grounded or VCC is disconnected.
CAP
RS485 Driver
VCC
28701 F14
VDD
GND
C2
1μF
Figure 14. Supply Current Overshoot Protection
for Input Supplies of 4.5V of Higher
The RS485 driver provides full RS485/RS422 compatibility. 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.
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. The maximum current in this condition is 90mA
for the RS232 driver and 250mA for the RS485 driver.
If the RS485 driver output is shorted to a voltage greater
than VCC, when it is active, positive current of up to 100mA
may flow from the driver output back to VCC. If the system
power supply or loading cannot sink this excess current,
clamp VCC to GND with a Zener diode (e.g., 5.6V, 1W,
1N4734) to prevent an overvoltage condition on VCC.
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.
RS485 Balanced Receiver with Full Failsafe Operation
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.
The LTC2870 and LTC2871 receivers use a window comparator with two voltage thresholds centered around zero
for low pulse width distortion. As illustrated in Figure 15, for
a differential signal approaching from a negative direction,
the threshold is typically +65mV. When approaching from
the positive direction, the threshold is typically –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.
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,
where a signal is driven through 4000 feet of CAT5e cable at
3Mbps. Even though the differential signal peaks at just over
±100mV and is heavily slewed, the output maintains a nearly
perfect signal with almost no duty cycle distortion.
An additional benefit of the window comparator architecture
is excellent noise immunity due to the wide effective differential hysteresis (or ‘AC’ hysteresis) of about 130mV for
normal signals transitioning through the window region in
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.
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.
B
0.1V/DIV
A
RO
(A-B)
RECEIVER
OUTPUT HIGH
0.1V/DIV
RECEIVER
OUTPUT LOW
–200mV
–65mV
0V
65mV
200mV
VAB
28701 F15
Figure 15. RS485 Receiver Input Threshold Characteristics
5V/DIV
RO
200ns/DIV
28701 F16
Figure 16. 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
28701f
21
LTC2870/LTC2871
APPLICATIONS INFORMATION
The RS232 and RS485 receiver outputs are internally
driven high (to VL) or low (to GND) with no external pullup needed. When the receivers are disabled the output pin
becomes Hi-Z with leakage of less than ±5μA for voltages
within the VL supply range.
RS485 Receiver Input Resistance
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
receivers per system without exceeding the RS485 receiver
loading specification. The input resistance of the receiver
is unaffected by enabling/disabling the receiver or whether
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.
125k
A
60Ω
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.
126
VCC = 5.0V
VCC = 3.3V
124
122
120
118
TE485
125k
through logic control, the proper line termination for correct 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.
RESISTANCE (Ω)
Receiver Outputs
60Ω
116
–10
–5
0
5
VOLTAGE (V)
10
15
28701 F18
B
28701 F17
Figure 17: Equivalent RS485 Receiver
Input Resistance Into A and B (Note 5)
Selectable RS485 Termination
Proper cable termination is important for good signal fidelity. When the cable is not terminated with its characteristic
impedance, reflections cause waveform distortion.
The LTC2870 and LTC2871 offer integrated switchable
120Ω termination resistors between the differential receiver
inputs and also between the differential driver outputs.
This provides the advantage of being able to easily change,
Figure 18. Typical Resistance of the Enabled RS485
Terminator vs Common Mode Voltage on A /B
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.
28701f
22
LTC2870/LTC2871
APPLICATIONS INFORMATION
Logic Loopback
A loopback mode connects the driver inputs to the receiver 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.
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.
CABLE LENGTH (FT)
10k
1k
LTC2870/LTC2871
MAX DATA RATE
100
RS485/RS422
MAX DATA RATE
10
10k
100k
1M
10M
DATA RATE (bps)
100M
28701 F19
Figure 19. Cable Length vs Data Rate (RS485/RS422
Standard Shown in Vertical Solid Line)
RS485 Cable Length vs Data Rate
For a given data rate, the maximum transmission distance 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 factors 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.
The solid vertical line represents the specified maximum
data rate in the RS485/RS422 standards. The dashed lines
at 20Mbps show the maximum data rates of the LTC2870
and LTC2871.
Layout Considerations
All VCC pins must be connected together on the PC board
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 VCC pin
that is adjacent to the VDD pin.
0.1μF capacitors to GND can be added on the VCC pins
adjacent to the B and VL pins if the connection to the 2.2μF
decoupling capacitor is not direct or if the trace is very
narrow. All GND pins must be connected together and
all VEE pins must be connected together, including the
exposed pad on the bottom of the package. The bypass
capacitor at VEE, C3, should be positioned closest to the
VEE pin that is adjacent to the CAP pin, with no more than
1cm of total trace length between the VEE and GND pins.
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.
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 differential signal integrity. To minimize capacitive loading
effects, the differential signals should be separated by
more than the width of a trace.
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, VL = 1.7V to VCC. Logic input pins not shown are tied to a valid logic state.
VL
VL
DXEN
LTC2870
485/232
VL
DXEN
RXEN
LTC2870
485/232
DXEN
RXEN
LB
LB
DY
DY
Y
LTC2870
H/F
TE485
LB
Y
Y
DY
RA
A
RA
A
DZ
Z
DZ
Z
120Ω
Z
A
RA
RB
RB
B
Figure 20. LTC2870 in
RS232 Mode
GND
DXEN
485/232
RXEN
H/F
LB
28701 F22
Figure 21. LTC2870 in RS232
Mode with Loopback
TE485
Figure 22. LTC2870 in RS485
Mode, Terminated
VL
VL
LTC2870
B
28701 F21
28701 F20
VL
120Ω
B
GND
GND
RXEN
485/232
DXEN
LTC2870
485/232
RXEN
DXEN
TE485
485/232
LB
H/F
LTC2870
RXEN
LB
H/F
Y
Y
TE485
DY
DY
Y
Z
Z
DY
120Ω
Z
A
A
RA
RA
RA
B
120Ω
B
GND
GND
28701 F23
Figure 23. LTC2870 in RS485
Mode in Loopback
GND
28701 F24
Figure 24. LTC2870 in RS485
Mode Half-Duplex
28701 F25
Figure 25. LTC2870 in RS485
Mode, Half-Duplex, with
Loopback and Terminated
28701f
24
LTC2870/LTC2871
TYPICAL APPLICATIONS
VCC = 3V to 5.5V, VL = 1.7V to VCC. Logic input pins not shown are tied to a valid logic state.
VL
VL
VL
DXEN
LTC2870
RXEN
DX485
H/F
RX232
TE485
LTC2871
LB
RS RS
232 485
485/232
DY
DX232
DX232
RX485
RX485
LTC2871
DX485
RX232
CH2
CH2
TE485
TE485
H/F
H/F
LB
LB
Y
Y
DI
120Ω
DZ
Z
RA
A
Z
DIN1
A
ROUT1
B
DIN2
DOUT1
RIN1
RO
ROUT2
120Ω
RIN2
B
RB
GND
Figure 26. LTC2870 Protocol Switching
VL
LTC2871
GND
GND
28701 F26
DX232
DOUT2
DX485
28701 F28
28701 F27
Figure 27. LTC2871 in RS485 Mode
Figure 28. LTC2871 in RS232 Mode
VL
VL
DX232
LTC2871
RX232
DX232
CH2
DX485
RX485
RX232
CH2
TE485
RX485
LB
H/F
TE485
TE485
LB
H/F
DX485
LTC2871
RX232
CH2
RX485
H/F
LB
Y
Y
DI
120Ω
DI
Z
Z
DIN1
DOUT1
ROUT1
RIN1
A
A
RO
B
DIN1
120Ω
RO
B
DIN1
DOUT1
DOUT1
ROUT1
RIN1
RIN1
ROUT1
DIN2
DIN2
ROUT2
RIN2
GND
GND
28701 F29
Figure 29. LTC2871 Single
RS232 Channel Active
DOUT2
DOUT2
RIN2
ROUT2
GND
28701 F30
Figure 30. LTC2871 in
RS485 and RS232 Mode
28701 F31
Figure 31. LTC2871 in RS485 and
RS232 Mode with Loopback and
RS485 Termination
28701f
25
LTC2870/LTC2871
TYPICAL APPLICATIONS
VCC = 3V to 5.5V, VL = 1.7V to VCC. Logic input pins not shown are tied to a valid logic state.
VL
VL
VL
H/F
LTC2871
CH2
DX232
LB
DX485
TE485
D R 485
DX485
LTC2871
RX232
DX232
CH2
DX485
H/F
RX485
H/F
LB
TE485
TE485
LTC2871
RX232
CH2
RX485
LB
RX485
DX232
D R 232
RX232
Y
Y
Y
DI
DI
DI
Z
120Ω
Z
Z
A
RO
RO
RO
DIN1
DIN1
B
DIN1
DOUT1
RIN1
ROUT1
RIN1
ROUT1
DIN2
DIN2
RIN2
RIN1
ROUT1
DIN2
DOUT2
RIN2
ROUT2
RIN2
ROUT2
GND
GND
GND
28701 F32
Figure 32. LTC2871 in RS485 and
RS232 Mode, Both Half-Duplex
DOUT1
DOUT2
DOUT2
ROUT2
120Ω
DOUT1
28701 F34
28701 F33
Figure 33. LTC2871 in RS485 and RS232
Mode, RS485 Half-Duplex, Loopback
Figure 34. LTC2871 in RS485
and RS232 Mode, RS485
Half-Duplex, Terminated
VL
485/232
LTC2870/
LTC2871
H/F
3V TO 5.5V
LB
TE485
1.7V TO VCC
LTC2870/
LTC2871
VCC
VL
LTC2870/
LTC2871
CONTROL
SIGNALS
Y
DI
Z
DY
RS485
FULL HALF
DY, DIN1
Y
RA, ROUT1
A
DZ, DIN2
Z
RB, ROUT2
B
120Ω
H/F
μP
RS232
DUPLEX
28701 F37
A
RO
120Ω
B
RB
GND
28701 F36
GND
Figure 36. Microprocessor Interface
28701 F35
DATA RATE CL
100kbps 5nF
500kbps 1nF
CL
3k
Figure 37. Driving Larger
RS232 Loads
Figure 35. RS485 Duplex Switching
28701f
26
LTC2870/LTC2871
TYPICAL APPLICATIONS
1.7V TO VCC
VL
VL
3V TO 5.5V
LTC2870
VCC
DXEN
RXEN
485/232
H/F
RS485
FULL-DUPLEX
RS485
HALF-DUPLEX
RS232
FULL-DUPLEX
485/232 = 1
H/F = 0
485/232 = 1
H/F = 1
485/232 = 0
H/F = X
RS485
RS485
RS232
RS485
RS485
RS232
TE485
DY
Y
CONTROLLER
Z
DZ
CONNECTOR
RA
A
B
RS485
RS232
RS485
RS232
RB
GND
28701 F38
Figure 38. LTC2870: Making Use of Shared I/O for Various Communication Configurations
1.7V TO VCC
VL
VL
3V TO 5.5V
LTC2870
DXEN
VCC
TE485
RXEN
485/232
H/F
RS485
HALF-DUPLEX
RS232
HALF-DUPLEX
DY
485/232 = 1
H/F = 0
485/232 = 0
H/F = X
RS485
RS232
RS485
RS232
Y
CONTROLLER
Z
CONNECTOR
DZ
RA
A
B
RB
GND
28701 F39
Figure 39. LTC2870: Using External Connections for Half-Duplex RS232 or RS485 Operation
28701f
27
LTC2870/LTC2871
TYPICAL APPLICATIONS
1.7V TO VCC
VL
DX232
RX232
DX485
RX485
H/F
TE485
VL
3V TO 5.5V
LTC2871
VCC
RS232
FULL-DUPLEX
RS232
FULL-DUPLEX
RS485
FULL-DUPLEX
RS485
HALF-DUPLEX
H/F = 0
H/F = 1
RS232
RS232
RS485
RS485
RS485
RS485
RS232
RS232
RS232
RS232
DOUT1
DIN1
Y
DI
Z
CONTROLLER
DOUT2
DIN2
CONNECTOR
ROUT1
RIN1
RS485
A
RO
RS485
B
ROUT2
RS232
RIN2
RS232
GND
28701 F40
Figure 40. LTC2871: Various Communication Configurations
1.7V TO VCC
VL
VL
3V TO 5.5V
LTC2871
DX232
RX232
DX485
RX485
H/F
TE485
DIN1
VCC
DOUT1
Y
DI
Z
CONTROLLER
DOUT2
DIN2
RS232
HALF-DUPLEX
RS232
HALF-DUPLEX
RS485
FULL-DUPLEX
RS485
HALF-DUPLEX
H/F = 0
H/F = 1
RS232
RS232
RS485
RS485
RS485
RS485
RS232
RS232
CONNECTOR
RIN1
ROUT1
A
RO
B
RS485
RS485
RIN2
ROUT2
GND
28701 F41
Figure 41. LTC2871: More Communication Configurations Using External Connections
28701f
28
LTC2870/LTC2871
TYPICAL APPLICATIONS
VCC = 3V to 5.5V, VL = 1.7V to VCC. Logic input pins not shown are tied to a valid logic state.
VL
VL
DX232
LTC2871
RX232
RX232
LB
DX485
LB
RX485
CH2
DI
120Ω
CH2
H/F
Y
A
Z
B
TE485
RO
120Ω
ROUT1
RXIN
DIN1
RIN1
DOUT1
RS485
ROUT1
RIN1
ROUT1
DIN1
RO
120Ω
RXOUT
RS232
UP TO 4000 FT
CAT5e CABLE
RS232
DRIVER
OUT
DX232
DX485
RX485
H/F
TE485
LTC2871
A
Y
B
Z
DI
120Ω
GND
DRIVER
IN
GND
28701 F42
Figure 42. RS232 Extension Cord Using RS232 to RS485 Conversion
SLAVE
SLAVE
LTC2852
LTC2852
SLAVE
MASTER
LTC2870/LTC2871
LTC2855
120Ω
120Ω
120Ω
3.3V
VL
TE485
TE
28701 F43
Figure 43. RS485 Full-Duplex Network
28701f
29
LTC2870/LTC2871
TYPICAL APPLICATIONS
LTC2871
DIN1
PORT 1
LOGIC
INTERFACE
ROUT1
RIN1
DIN2
PORT 2A/2B
LOGIC
INTERFACE
LTC2871
DOUT1
DIN1
PORT 1
LINE
INTERFACE
PORT 1
LOGIC
INTERFACE
PORT 2A
LINE
INTERFACE
PORT 2A
LOGIC
INTERFACE
DOUT2
ROUT2
RIN2
RIN1
PORT 1
LINE
INTERFACE
DOUT2
ROUT2
PORT 2A/2B
LINE
INTERFACE
RIN2
CH2
SELECT LINE 2A
SELECT LINE 2A
LTC2871
SELECT LINE 2B
CH2
DIN2
ROUT2
DIN1
PORT 3
LOGIC
INTERFACE
ROUT1
DIN2
CH2
SELECT LINE 2B
DOUT1
ROUT1
DOUT2
RIN2
DIN2
PORT 2B
LINE
INTERFACE
PORT 2B
LOGIC
INTERFACE
PORT 3
LINE
INTERFACE
PORT 3
LOGIC
INTERFACE
DOUT1
RIN1
LTC2871
CH2
ROUT2
DIN1
ROUT1
28701 F44
DOUT2
RIN2
DOUT1
RIN1
PORT 3
LINE
INTERFACE
28701 F45
Figure 44. RS232 Triple Transceiver
with Selectable Line Interface
Figure 45. RS232 Triple Transceiver
with Selectable Logic Interface
LTC2870/
LTC2871
SELECT
H/F
INPUT2 INPUT1
Y
RS485
INTERFACE
Z
RA,
RO
INPUT1
A
B
INPUT2
28701 F46
Figure 46. RS485 Receiver with Multiplexed Inputs
28701f
30
LTC2870/LTC2871
TYPICAL APPLICATIONS
3V TO 5.5V
220nF
10μH
2.2μF
1.7V TO VCC
VCC
SW
220nF
CAP
CAP
VCC
SW
LTC2870
LTC2871
H/F
H/F
2.2μF
0.1μF
TE485
TE485
RS485
INTERFACE
Y
DI
120Ω
RO
485/232
Y
Z
Z
A
A
RA
120Ω
B
DIN1
DY
120Ω
120Ω
B
DOUT1
ROUT1
RIN1
DIN2
1μF
1.7V TO VCC
VL
VL
0.1μF
3V TO 5.5V
10μH
RS232
INTERFACE
DOUT2
ROUT2
RIN2
VDD
GND
VDD
VEE
1μF
VEE
GND
28701 F47
1μF
1μF
Figure 47. Typical Supply Connections with External Components Shown
3V TO 5.5V
470nF
22μH
2.2μF
VCC
VL
GND
CAP
SW
CAP
LTC2870/
LTC2871
VDD
VCC
LTC2870/
LTC2871
VEE
VEE
VDD
VL
SW
GND
28701 F48
2.2μF
2.2μF
INDUCTOR: TAIYO YUDEN CBC2518T220M,
MURATA LQH32CN220K53
Figure 48. Running Two LTC2870 or LTC2871 Devices from One Shared Power Source
28701f
31
LTC2870/LTC2871
PACKAGE DESCRIPTION
FE Package
28-Lead 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)
4.50 ±0.10
SEE NOTE 4
0.45 ±0.05
EXPOSED
PAD HEAT SINK
ON BOTTOM OF
PACKAGE
6.40
2.74
(.252)
(.108)
BSC
1.05 ±0.10
0.65 BSC
RECOMMENDED SOLDER PAD LAYOUT
4.30 – 4.50*
(.169 – .177)
0.09 – 0.20
(.0035 – .0079)
0.50 – 0.75
(.020 – .030)
NOTE:
1. CONTROLLING DIMENSION: MILLIMETERS
2. DIMENSIONS ARE IN MILLIMETERS
(INCHES)
3. DRAWING NOT TO SCALE
1 2 3 4 5 6 7 8 9 10 11 12 13 14
0.25
REF
1.20
(.047)
MAX
0° – 8°
0.65
(.0256)
BSC
0.195 – 0.30
(.0077 – .0118)
TYP
0.05 – 0.15
(.002 – .006)
FE28 (EB) TSSOP 0204
4. RECOMMENDED MINIMUM PCB METAL SIZE
FOR EXPOSED PAD ATTACHMENT
*DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.150mm (.006") PER SIDE
28701f
32
LTC2870/LTC2871
PACKAGE DESCRIPTION
FE Package
38-Lead Plastic TSSOP (4.4mm)
(Reference LTC DWG # 05-08-1772 Rev A)
Exposed Pad Variation AA
4.75 REF
38
9.60 – 9.80*
(.378 – .386)
4.75 REF
(.187)
20
6.60 ±0.10
2.74 REF
4.50 REF
SEE NOTE 4
6.40
2.74
REF (.252)
(.108)
BSC
0.315 ±0.05
1.05 ±0.10
0.50 BSC
RECOMMENDED SOLDER PAD LAYOUT
4.30 – 4.50*
(.169 – .177)
0.09 – 0.20
(.0035 – .0079)
0.50 – 0.75
(.020 – .030)
NOTE:
1. CONTROLLING DIMENSION: MILLIMETERS
2. DIMENSIONS ARE IN MILLIMETERS
(INCHES)
3. DRAWING NOT TO SCALE
1
0.25
REF
19
1.20
(.047)
MAX
0o – 8o
0.50
(.0196)
BSC
0.17 – 0.27
(.0067 – .0106)
TYP
0.05 – 0.15
(.002 – .006)
FE38 (AA) TSSOP 0608 REV A
4. RECOMMENDED MINIMUM PCB METAL SIZE
FOR EXPOSED PAD ATTACHMENT
*DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.150mm (.006") PER SIDE
28701f
33
LTC2870/LTC2871
PACKAGE DESCRIPTION
UFD Package
28-Lead 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
4.00 ± 0.10
(2 SIDES)
0.75 ± 0.05
R = 0.05
TYP
PIN 1 NOTCH
R = 0.20 OR 0.35
× 45° CHAMFER
2.50 REF
R = 0.115
TYP
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
0.200 REF
0.00 – 0.05
0.25 ± 0.05
0.50 BSC
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-Lead Plastic QFN (5mm × 7mm)
(Reference LTC DWG # 05-08-1701 Rev C)
0.70 p 0.05
5.50 p 0.05
5.15 ± 0.05
4.10 p 0.05
3.00 REF
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
5.00 p 0.10
0.75 p 0.05
PIN 1 NOTCH
R = 0.30 TYP OR
0.35 s 45o CHAMFER
3.00 REF
37
0.00 – 0.05
38
0.40 p0.10
PIN 1
TOP MARK
(SEE NOTE 6)
1
2
5.15 ± 0.10
7.00 p 0.10
5.50 REF
3.15 ± 0.10
(UH) QFN REF C 1107
0.200 REF 0.25 p 0.05
0.50 BSC
R = 0.125
TYP
R = 0.10
TYP
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING CONFORMS TO JEDEC PACKAGE
OUTLINE M0-220 VARIATION WHKD
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 0.20mm 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
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 representation 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
VCC
VL
CAP
SW
CAP
VCC
LTC2871
T1IN
TE485
DOUT1
DIN1
RIN1
ROUT1
DOUT2
DIN2
RIN2
ROUT2
VL
LTC2804
SW
T1OUT1
ROUT1
RIN1
T2IN
T2OUT
ROUT2
VEE
RIN2
VDD
GND
RO
120Ω
B
DI
GND
3.3V
A
VDD
LTC2854
Y
A
120Ω
Z
B
VCC
0.1μF
TE
DI
120Ω
RO
VEE
GND
2.2μF
2.2μF
28701 TA02
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC1334
Single 5V RS232/RS485 Multiprotocol Transceiver
Dual Port, Single 5V Supply, Configurable, 10kV ESD
LTC1387
Single 5V RS232/RS485 Multiprotocol Transceiver
Single Port, Configurable
LTC2801/LTC2802/
LTC2803/LTC2804
1.8V to 5.5V RS232 Single and Dual Transceivers
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
LTC2859/LTC2861
20Mbps RS485 Transceiver with Integrated
Switchable Termination
5V Supply, Integrated, Switchable, 120Ω Termination Resistor, 15kV ESD
LTM2881
Complete Isolated RS485/RS422 μModule
Transceiver + Power
20Mbps, 2500VRMS Isolation with Integrated DC/DC Converter, Integrated,
Switchable, 120Ω Termination Resistor, 15kV ESD
LTM2882
Dual Isolated RS232 μModule Transceiver + Power
1Mbps, 2500VRMS Isolation with Integrated DC/DC Converter, ±10kV ESD
28701f
36 Linear Technology Corporation
LT 1210 • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2010