LINER LTC2854 ±60v fault protected 3v to 5.5v rs485/rs422 transceiver with level 4 iec esd Datasheet

LTC2862A
±60V Fault Protected 3V to 5.5V
RS485/RS422 Transceiver
with Level 4 IEC ESD
Description
Features
Protected from Overvoltage Line Faults to ±60V
nn 3V to 5.5V Supply Voltage
nn 20Mbps or Low EMI 250kbps Data Rate
nn ±40kV HBM ESD Interface Pins, ±15kV Other Pins
nn Enhanced Receiver and Failsafe Noise Immunity
nn IEC Level 4 ESD and EFT on Interface Pins
nn Extended Common Mode Range: ±25V
nn Guaranteed Failsafe Receiver Operation
nn High Input Impedance Supports 224 Nodes
nn MP-Grade Option Available (–55°C to 125°C)
nn Fully Balanced Differential Receiver Thresholds for
Low Duty Cycle Distortion
nn Current Limited Drivers and Thermal Shutdown
nn Compliant with TIA/EIA-485-A
nn Pin Compatible with LTC2862 and LT®1785
nn Available in DFN and Leaded Packages
The LTC®2862A is a low power, 20Mbps or 250kbps RS485/
RS422 transceiver operating on 3V to 5.5V supplies with
±60V overvoltage fault protection on the interface pins
during all modes of operation, including power-down.
Improvements were made to the LTC2862 for greater robustness and signal integrity: ±40kV HBM and Level 4 IEC
ESD protection on the interface pins; increased resistance
to electrical overstress; increased receiver noise immunity;
additional receiver noise filtering on the LTC2862A-2; and
an improved failsafe function optimized for high speed in
the LTC2862A-1 and noise rejection in the LTC2862A-2.
Low EMI slew rate limited data transmission is available
in the 250kbps LTC2862A-2 option, while the LTC2862A-1
operates to 20Mbps.
nn
Extended ±25V input common mode range and full failsafe operation improve data communication reliability in
electrically noisy environments and in the presence of
large ground loop voltages.
Applications
Supervisory Control and Data Acquisition (SCADA)
Industrial Control and Instrumentation Networks
nn Automotive and Transportation Electronics
nn Building Automation, Security Systems and HVAC
nn Medical Equipment
nn Lighting and Sound System Control
nn
Product Selection Guide
nn
PART NUMBER
DUPLEX
ENABLES
MAX DATA
RATE (bps)
LTC2862A-1
HALF
YES
20M
LTC2862A-2
HALF
YES
250k
L, LT, LTC, LTM, Linear Technology the Linear logo and µModule are registered trademarks of
Analog Devices, Inc.. All other trademarks are the property of their respective owners.
Typical Application
LTC2862A-1 Receiving 10Mbps ±200mV Differential
Signal with 1MHz ±25V Common Mode Sweep
RS485 Link With Large Ground Loop Voltage
LTC2862A
LTC2862A
R
RO1
RE1
DE1
DI1
R
D
RO2
RE2
DE2
D
GND1
V GROUND LOOP
≤25V PEAK
GND2
A,B
A,B
50V/DIV
VCC2
VCC1
2862A TA01a
DI2
A–B
0.5V/DIV
RO
5V/DIV
A–B
RO
100ns/DIV
2862A TA01b
2862af
For more information www.linear.com/LTC2862A
1
LTC2862A
Absolute Maximum Ratings
(Note 1)
Supply Voltages
VCC............................................................. –0.3 to 6V
Logic Input Voltages (RE, DE, DI)................... –0.3 to 6V
Interface I/O: A, B...................................... –60V to +60V
Receiver Output (RO).......................–0.3V to (VCC+0.3V)
Operating Ambient Temperature Range (Note 4)
LTC2862AC............................................... 0°C to 70°C
LTC2862AI............................................–40°C to 85°C
LTC2862AH........................................ –40°C to 125°C
LTC2862AMP...................................... –55°C to 125°C
Storage Temperature Range................... –65°C to 150°C
Pin Configuration
LTC2862A-1, LTC2862A-2
LTC2862A-1, LTC2862A-2
TOP VIEW
TOP VIEW
RO 1
8
VCC
RE 2
7
B
DE 3
6
A
DI 4
5
GND
S8 PACKAGE
8-LEAD (150mil) PLASTIC SO
TJMAX = 150°C, θJA = 120°C/W, θJC = 39°C/W
Order Information
RO
1
RE
2
DE
3
DI
4
8 VCC
9
7 B
6 A
5 GND
DD PACKAGE
8-LEAD (3mm × 3mm) PLASTIC DFN
EXPOSED PAD (PIN 9) CONNECT TO PCB GND
TJMAX = 150°C, θJA = 43°C/W, θJC = 5.5°C/W
http://www.linear.com/product/LTC2862A#orderinfo
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC2862ACS8-1#PBF
LTC2862ACS8-1#TRPBF
2862A1
8-Lead (150mil) Plastic SO
0°C to 70°C
LTC2862AIS8-1#PBF
LTC2862AIS8-1#TRPBF
2862A1
8-Lead (150mil) Plastic SO
–40°C to 85°C
LTC2862AHS8-1#PBF
LTC2862AHS8-1#TRPBF
2862A1
8-Lead (150mil) Plastic SO
–40°C to 125°C
LTC2862AMPS8-1#PBF
LTC2862AMPS8-1#TRPBF
2862A1
8-Lead (150mm) Plastic SO
–55°C to 125°C
LTC2862ACS8-2#PBF
LTC2862ACS8-2#TRPBF
2862A2
8-Lead (150mil) Plastic SO
0°C to 70°C
LTC2862AIS8-2#PBF
LTC2862AIS8-2#TRPBF
2862A2
8-Lead (150mil) Plastic SO
–40°C to 85°C
LTC2862AHS8-2#PBF
LTC2862AHS8-2#TRPBF
2862A2
8-Lead (150mil) Plastic SO
–40°C to 125°C
LTC2862AMPS8-2#PBF
LTC2862AMPS8-2#TRPBF
2862A2
8-Lead (150mm) Plastic SO
–55°C to 125°C
LTC2862ACDD-1#PBF
LTC2862ACDD-1#TRPBF
LGYK
8-Lead (3mm × 3mm) Plastic DFN
0°C to 70°C
LTC2862AIDD-1#PBF
LTC2862AIDD-1#TRPBF
LGYK
8-Lead (3mm × 3mm) Plastic DFN
–40°C to 85°C
LTC2862AHDD-1#PBF
LTC2862AHDD-1#TRPBF
LGYK
8-Lead (3mm × 3mm) Plastic DFN
–40°C to 125°C
LTC2862ACDD-2#PBF
LTC2862ACDD-2#TRPBF
LGYM
8-Lead (3mm × 3mm) Plastic DFN
0°C to 70°C
LTC2862AIDD-2#PBF
LTC2862AIDD-2#TRPBF
LGYM
8-Lead (3mm × 3mm) Plastic DFN
–40°C to 85°C
LTC2862AHDD-2#PBF
LTC2862AHDD-2#TRPBF
LGYM
8-Lead (3mm × 3mm) Plastic DFN
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
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/
2
2862af
For more information www.linear.com/LTC2862A
LTC2862A
Electrical Characteristics
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 3.3V unless otherwise noted. (Note 2)
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Supplies
VCC
Primary Power Supply
5.5
V
ICCS
Supply Current in Shutdown Mode
(C-, I-Grade)
DE = 0V, RE = VCC
l
0
10
µA
Supply Current in Shutdown Mode
(H-, MP-Grade)
DE = 0V, RE = VCC
l
0
40
µA
ICCTR
Supply Current with Both Driver and
Receiver Enabled (LTC2862A-1)
No Load, DE = VCC , RE = 0V
l
1.1
1.6
mA
ICCR
Supply Current with Receiver Enabled
(LTC2862A-1)
No Load, DE = RE = 0V
l
1.0
1.4
mA
ICCTRS
Supply Current with Both Driver and
Receiver Enabled (LTC2862A-2)
No Load, DE = VCC , RE = 0V
l
3.5
8
mA
ICCRS
Supply Current with Receiver Enabled
(LTC2862A-2)
No Load, DE = RE = 0V
l
1.3
1.8
mA
Differential Driver Output Voltage
R = ∞ (Figure 1)
l
1.5
3
VCC
V
R = 27Ω (Figure 1)
l
1.5
2
5
V
R = 50Ω (Figure 1)
l
2
2.3
VCC
V
l
3
Driver
|VOD|
Δ|VOD|
Change in Magnitude of Driver Differential
Output Voltage
R = 27Ω or 50Ω (Figure 1)
l
0
0.2
V
VOC
Driver Common-Mode Output Voltage
R = 27Ω or 50Ω (Figure 1)
l
2
3
V
Δ|VOC|
Change in Magnitude of Driver
Common-Mode Output Voltage
R = 27Ω or 50Ω (Figure 1)
l
0
0.2
V
IOSD
Maximum Driver Short-Circuit Current
–60V ≤ (A or B) ≤ 60V (Figure 2)
l
±150
±250
mA
VCC = 0V or 3.3V, VIN = 12V (Figure 3)
l
143
µA
VCC = 0V or 3.3V, VIN = –7V (Figure 3)
l
Receiver
IIN
Receiver Input Current (A, B)
RIN
Receiver Input Resistance
VCM
Receiver Common Mode Input Voltage
(A + B)/2
VTH+
Positive Differential Input Signal Threshold
Voltage (A – B)
–25V ≤ VCM ≤ 25V
l
VTH–
Negative Differential Input Signal Threshold –25V ≤ VCM ≤ 25V
Voltage (A – B)
l
ΔVTH
Differential Input Signal Hysteresis
(VTH+ – VTH–)
VTFS
Differential Input Failsafe Threshold Voltage –25V ≤ VCM ≤ 25V
ΔVTFS
Differential Input Failsafe Hysteresis
(VTFS – VTH–)
VCM = 0V
VOH
Receiver Output High Voltage
I(RO) = –3mA (Sourcing)
l
VOL
Receiver Output Low Voltage
I(RO) = 3mA (Sinking)
l
IOZR
Receiver Three-State (High Impedance)
Output Current on RO
RE = High, VCC = 5V, RO = 0V or VCC
l
IOSR
Receiver Short-Circuit Current
RE = Low, RO = 0V or VCC
l
CIN
Input Capacitance (A and B)
(Note 5)
–100
0 ≤ VCC ≤ 5.5V, VIN = –25V or 25V (Figure 3)
µA
112
l
–25
125
–200
VCM = 0V
l
–200
kΩ
25
V
200
mV
–125
mV
250
mV
–75
–10
50
VCC –0.4V
mV
VCC –0.2V
0.2
–32
50
mV
V
0.4
V
5
µA
±20
mA
pF
2862af
For more information www.linear.com/LTC2862A
3
LTC2862A
Electrical Characteristics
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 3.3V unless otherwise noted. (Note 2)
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Logic
VTH
Input Threshold Voltage (DE, DI, RE)
3.0 ≤ VCC ≤ 5.5V
l
IINL
Logic Input Current (DE, DI, RE)
0 ≤ VIN ≤ VCC
l
0.33 • VCC
0.67 • VCC
V
±5
µA
0
ESD (Note 5)
ESD Protection Level of Interface Pins
(A,B), Powered or Unpowered
ESD Protection Level of All Other Pins
(RO, RE, DE, DI, VCC, GND)
Human Body Model, A or B to GND,
VCC, B or A, 1μF Between VCC and GND
±40kV
kV
IEC 61000-4-2 ESD Level 4, Contact, 1μF
Between VCC and GND
±8kV
kV
Human Body Model
±15kV
kV
Switching Characteristics
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 3.3V unless otherwise noted. (Note 2)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Driver – High Speed (LTC2862A-1)
fMAX
Maximum Data Rate
(Note 3)
l
tPLHD, tPHLD
ΔtPD
20
Mbps
Driver Input to Output
RDIFF = 54Ω, CL = 100pF (Figure 4)
l
25
50
ns
Driver Input to Output Difference
|tPLHD – tPHLD|
RDIFF = 54Ω, CL = 100pF (Figure 4)
l
2
5
ns
tSKEWD
Driver Output A to Output B
RDIFF = 54Ω, CL = 100pF (Figure 4)
l
±10
ns
tRD, tFD
Driver Rise or Fall Time
RDIFF = 54Ω, CL = 100pF (Figure 4)
l
4
15
ns
tZLD, tZHD
Driver Enable Time
RL = 27Ω, CL = 100pF,
RE = 0V (Figure 5)
l
25
50
ns
tLZD, tHZD
Driver Disable Time
RL = 27Ω, CL = 100pF,
RE = 0V (Figure 5)
l
45
75
ns
tZHSD, tZLSD
Driver Enable from Shutdown
RL = 27Ω, CL = 100pF,
RE = High (Figure 5)
l
5
10
µs
tSHDND
Time to Shutdown
RL = 27Ω, CL = 100pF,
RE = High (Figure 5)
l
50
90
ns
(Note 3)
l
RDIFF = 54Ω, CL = 100pF (Figure 4)
l
850
1500
ns
10
150
ns
±500
ns
800
1200
ns
Driver – Slew Rate Limited (LTC2862A-2)
fMAXS
Maximum Data Rate
tPLHDS, tPHLDS Driver Input to Output
250
kbps
ΔtPDS
Driver Input to Output Difference
|tPLHDS – tPHLDS|
RDIFF = 54Ω, CL = 100pF (Figure 4)
l
tSKEWDS
Driver Output A to Output B
RDIFF = 54Ω, CL = 100pF (Figure 4)
l
tRDS, tFDS
Driver Rise or Fall Time
RDIFF = 54Ω, CL =100pF (Figure 4)
l
tZLDS, tZHDS
Driver Enable Time
RL = 27Ω, CL = 100pF,
RE = 0V (Figure 5)
l
400
800
ns
tLZDS, tHZDS
Driver Disable Time
RL = 27Ω, CL = 100pF,
RE = 0V (Figure 5)
l
45
75
ns
RL = 27Ω, CL = 100pF,
RE = High (Figure 5)
l
6
11
µs
tZHSDS, tZLSDS Driver Enable from Shutdown
4
500
2862af
For more information www.linear.com/LTC2862A
LTC2862A
Switching Characteristics
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 3.3V unless otherwise noted. (Note 2)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
tSHDNDS
Time to Shutdown
RL = 27Ω, CL = 100pF,
RE = High (Figure 5)
Receiver Input to Output (LTC2862A-1)
tPLHRS, tPHLRS Receiver Input to Output (LTC2862A-2)
UNITS
l
50
90
ns
CL = 15pF, VCM = 0V, |VAB| = 1.5V,
tR and tF < 4ns (Figure 6)
l
50
65
ns
CL = 15pF, VCM = 0V, |VAB| = 1.5V,
tR and tF < 4ns (Figure 6)
l
400
700
ns
Receiver
tPLHR, tPHLR
tSKEWR
Differential Receiver Skew
|tPLHR – tPHLR| (LTC2862A-1)
CL = 15pF (Figure 6)
l
1
5
ns
tSKEWRS
Differential Receiver Skew
|tPLHRS – tPHLRS| (LTC2862A-2)
CL = 15pF (Figure 6)
l
5
30
ns
tPFSN
Failsafe Enter Delay (LTC2862A-1)
CL = 15pF, VCM = 0V, |VAB| = 1.5V,
tR and tF < 4ns (Figure 8)
l
80
110
ns
tPFSNS
Failsafe Enter Delay (LTC2862A-2)
CL = 15pF, VCM = 0V, |VAB| = 1.5V,
tR and tF < 4ns (Figure 8)
l
1.5
2.3
µs
tPFSX
Failsafe Exit Delay (LTC2862A-1)
CL = 15pF, VCM = 0V, |VAB| = 1.5V,
tR and tF < 4ns (Figure 8)
l
45
60
ns
tPFSXS
Failsafe Exit Delay (LTC2862A-2)
CL = 15pF, VCM = 0V, |VAB| = 1.5V,
tR and tF < 4ns (Figure 8)
l
0.7
1.3
µs
tRR, tFR
Receiver Output Rise or Fall Time
CL = 15pF (Figure 6)
l
3
6
ns
tZLR, tZHR
Receiver Enable Time
RL = 500Ω, CL = 15pF, DE = High
(Figure 7)
l
18
30
ns
tLZR, tHZR
Receiver Disable Time
RL = 500Ω, CL = 15pF, DE = High
(Figure 7)
l
29
40
ns
tZHSR, tZLSR
Receiver Enable from Shutdown
RL = 500Ω, CL = 15pF, DE = High
(Figure 7)
l
5
10
µs
tSHDNR
Time to Shutdown
RL = 500Ω, CL = 15pF, DE = High
(Figure 7)
l
24
40
ns
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: Maximum data rate is guaranteed by other measured parameters
and is not tested directly.
Note 4: This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed 150ºC when overtemperature protection is active.
Continuous operation above the specified maximum operating temperature
may result in device degradation or failure.
Note 5: Not tested in production.
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5
LTC2862A
Typical Performance Characteristics
ICCTRS
SUPPLY CURRENT (µA)
3.0
2.5
2.0
1.5
ICCTR
100
10
1
ICCS
0.5
0
3.0
4.0
4.5
VCC (V)
3.5
0.1
–50
5.5
5.0
2862A G01
60
–0.5
40
SLEW LIMITED
20
–1.0
DRIVER DELAY (NON SLEW LIMITED) (ns)
DRIVER SKEW (NON SLEW LIMITED) (ns)
0.0
0
150
50
100
TEMPERATURE (°C)
1000
SLEW LIMITED
30
800
NON SLEW LIMITED
20
–50
0
50
100
TEMPERATURE (°C)
2.3
2.0
1.5
50
0
–50
–100
OUTPUT HIGH
–200
–60
–40
–20
0
20
OUTPUT VOLTAGE (V)
RDIFF = 100Ω
2.1
1.9
RDIFF = 54Ω
1.7
40
60
2862A G06
Receiver Output Voltage vs
Output Current (Source and Sink)
6.0
1.0
VOL
OUTPUT LOW
100
–150
2.5
VOD (V)
DRIVER OUTPUT VOLTAGE (V)
150
Driver Differential Output Voltage
vs Temperature
VOH
0
60
45
50
55
40
SUPPLY CURRENT (mA)
200
700
150
2.5
0.0
35
2862A G05
3.5
VCC = 5.5V
5.0
4.0
VCC = 3.3V
3.0
2.0
1.0
VCC = 3V TO 5.5V
0
10
20
30
40
OUTPUT CURRENT (mA)
50
2862A G07
6
900
25
Driver Output Low/High Voltage
vs Output Current
0.5
30
Driver Output Short-Circuit
Current vs Voltage
RDIFF = 54Ω
CL = 100pF
2862A G04
3.0
50
4
2862A G03
DRIVER DELAY (SLEW LIMITED) (ns)
80
DRIVER SKEW (SLEW LIMITED) (ns)
100
0.5
0
35
120
NON SLEW LIMITED
–1.5
–50
NON SLEW LIMITED
Driver Propagation Delay vs
Temperature
RDIFF = 54Ω
CL = 100pF
1.0
100
8
2862A G02
Driver Skew vs Temperature
1.5
150
12
150
50
100
TEMPERATURE (°C)
200
SLEW LIMITED
0
0
250
RDIFF = 54Ω
CL = 100pF
16
OUTPUT CURRENT (mA)
1.0
ICCTR
RECEIVER OUTPUT VOLTAGE (V)
SUPPLY CURRENT (mA)
ICCTRS
1000
3.5
20
DATA RATE (SLEW LIMITED) (kbps)
4.0
Supply Current vs Data Rate
Supply Current vs Temperature
10000
4.5
DATA RATE (NON SLEW LIMITED) (Mbps)
Supply Current vs VCC
TA = 25°C, VCC = 3.3V, unless otherwise noted.
1.5
–50
0
50
100
TEMPERATURE (°C)
150
2862A G08
0.0
4.0
6.0
0.0
8.0
2.0
OUTPUT CURRENT (ABSOLUTE VALUE) (mA)
2862A G09
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LTC2862A
Typical Performance Characteristics
Transmitter Propagation Delay
vs Temperature (LTC2862A-2)
740
100
32
720
90
tPHLD
28
tPLHD
26
tPHLDS
700
FAILSAFE DELAY (ns)
30
24
680
tPLHDS
660
640
–25
0
25
50
75
TEMPERATURE (°C)
100
125
600
–50
–25
0
25
50
75
TEMPERATURE (°C)
Failsafe Enter and Exit Delay
vs Temperature (LTC2862A-2)
100
0
25
50
75
TEMPERATURE (°C)
100
125
Receiver Propagation Delay
vs Temperature (LTC2862A-2)
475
43
RECEIVER DELAY (ns)
RECEIVER DELAY (ns)
450
1.0
tPLHR
42
41
tPHLR
tPFSXS
0
25
50
75
TEMPERATURE (°C)
–25
2862A G12
tPFSNS
–25
tPFSX
40
–50
125
44
1.2
0.6
–50
60
Receiver Propagation Delay
vs Temperature (LTC2862A-1)
1.6
0.8
70
2862A G11
2862A G10
1.4
tPFSN
80
50
620
22
–50
FAILSAFE DELAY (µs)
Failsafe Enter and Exit Delay
vs Temperature (LTC2862A-1)
34
TRANSMITTER DELAY (ns)
TRANSMITTER DELAY (ns)
Transmitter Propagation Delay
vs Temperature (LTC2862A-1)
TA = 25°C, VCC = 3.3V, unless otherwise noted.
100
125
2862A G13
40
–50
–25
0
25
50
75
TEMPERATURE (°C)
425
400
tPHLRS
375
tPLHRS
350
325
100
125
2862A G14
300
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
2862A G15
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7
LTC2862A
Pin Functions
PIN NAME
PIN NUMBER
DESCRIPTION
RO
1
Receiver Output. If the receiver output is enabled (RE low) and A–B > 200mV, then RO will be high.
If A–B < –200mV, then RO will be low. If the receiver inputs are open, shorted, or terminated without a
signal, RO will be high. Integrated 250kΩ pull-up to VCC.
RE
2
Receiver Enable. A low input enables the receiver. A high input forces the receiver output into a high
impedance state. If RE is high with DE low, the part will enter a low power shutdown state.
DE
3
Driver Enable. A high input on DE enables the driver. A low input will force the driver outputs into a high
impedance state. If DE is low with RE high, the part will enter a low power shutdown state.
DI
4
Driver Input. If the driver outputs are enabled (DE high), then a low on DI forces the driver noninverting
output A low and inverting output B high. A high on DI, with the driver outputs enabled, forces the
driver noninverting output A high and inverting output B low.
GND
5
Ground.
Exposed Pad
9
Connect the exposed pad on the DFN packages to GND.
B
7
Inverting Receiver Input and Inverting Driver Output.
Impedance is ~112kΩ in receive mode or unpowered.
A
6
Noninverting Receiver Input and Noninverting Driver Output.
Impedance is ~112kΩ in receive mode or unpowered.
VCC
8
Power Supply. 3V < VCC < 5.5V. Bypass with 1µF ceramic capacitor to GND for best ESD performance.
Function Table
LTC2862A
LOGIC INPUTS
MODE
DE
RE
0
0
Receive
0
1
Shutdown
1
0
Transceive
1
1
Transmit
* 250kΩ pull-up to VCC.
8
A, B
RO
RIN
RIN
Active
Active
Active
High-Z*
Active
High-Z*
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LTC2862A
Block Diagram
LTC2862A
VCC
VCC
250k
RO
RECEIVER
A*
RE
DE
DI
MODE CONTROL
LOGIC
B*
DRIVER
GND
2862A BD
* 40kV ESD
ALL OTHER PINS 15kV
Test Circuits
A
A
GND
OR DI
VCC
+
VOD
–
DRIVER
B
R
R
GND
OR DI
VCC
+
VOC
–
IOSD
DRIVER
B
2862A FO2
2862A FO1
Figure 1. Driver DC Characteristics
Figure 2. Driver Output Short-Circuit Current
IIN
VIN
+
–
+
–
A OR B
B OR A
RECEIVER
2862A FO3
V
RIN = IN
IIN
Figure 3. Receiver Input Current and Input Resistance
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9
LTC2862A
Test Circuits
VCC
DI
A
DI
CL
RDIFF
DRIVER
tPLHD
0V
VO
A, B
tPHLD
tSKEWD
1/2 VO
CL
B
2862A FO4
90%
(A–B)
10%
0
0
tRD
90%
10%
tFD
2862A F04b
Figure 4. Driver Timing Measurement
RL
A
VCC
OR DI
GND
1/2 VCC
1/2 VCC
1/2 VCC
DRIVER
RL
B
VCC
0V
CL
DE
DE
A OR B
1/2 VCC
CL
tLZD,
tSHDN
tZLD,
tZLSD
375mV
375mV
375mV
375mV
VOL
VOH
B OR A
1/2 VCC
2862A FO5
2862A F05b
tZHD,
tZHSD
tHZD,
tSHDN
Figure 5. Driver Enable and Disable Timing Measurements
10
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LTC2862A
TEST CIRCUITS
±VAB/2
A
VCM
tSKEWR = |tPLHR – tPHLR|
VAB
B
0
A–B
RO
RECEIVER
–VAB
CL
±VAB/2
tPLHR
VCC
90%
10%
RO
0
1/2 VCC
tPHLR
90%
1/2 VCC
10%
tRR
2862A FO6a
tFR
2862A F06b
Figure 6. Receiver Propagation Delay Measurements
0V OR VCC
VCC OR 0V
RE
A
B
RECEIVER
1/2 VCC
RE
1/2 VCC
tLZR
1/2 VCC
RO
CL
DI = 0V OR VCC
tZLR,
tZLSR
0V
RL
RO
VCC
VOL
VOH
RO
1/2 VCC
1/4 VCC
1/4 VCC
3/4 VCC
3/4 VCC
tZHR,
tZHSR
2862A FO7a
tHZR,
tSHDNR
2862A F07b
Figure 7. Receiver Enable/Disable Time Measurements
±VAB /2
VCM
±VAB /2
0
A–B
–VAB
A
B
RECEIVER
RO
CL
VCC
–200mV
tPFSN, tPFSNS
RO
0
tPFSX, tPFSXS
1/2 VCC
1/2 VCC
2862A F08b
2862A FO8a
Figure 8. Failsafe Delay Measurements
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11
LTC2862A
Applications Information
±60V Fault Protection
±25V Extended Common Mode Range
The LTC2862A is an improved overvoltage fault-tolerant
RS485/RS422 transceiver that operates from 3V to 5.5V
power supplies. Industrial installations may encounter
common mode voltages between nodes far greater than
the –7V to 12V range specified by the RS485 standards.
Standard RS485 transceivers can be damaged by voltages
above their typical absolute maximum ratings of –8V to
12.5V. The limited overvoltage tolerance of standard RS485
transceivers makes implementation of effective external
protection networks difficult without interfering with proper
data network performance within the –7V to 12V region of
RS485 operation. Replacing standard RS485 transceivers
with the rugged LTC2862A devices may eliminate field
failures due to overvoltage faults without using costly
external protection devices.
To further increase the reliability of operation and extend
functionality in environments with high common mode
voltages due to electrical noise or local ground potential
differences due to ground loops, the LTC2862A features
an extended common mode operating range of –25V
to 25V. This extended common mode range allows the
LTC2862A to transmit and receive under conditions that
would cause data errors and possible device damage in
competing products.
The ±60V fault protection of the LTC2862A is achieved by
using a high-voltage BiCMOS integrated circuit technology.
The naturally high breakdown voltage of this technology
provides protection in powered-off and high-impedance
conditions. The driver outputs use a progressive foldback
current limit design to protect against overvoltage faults
while still allowing high current output drive.
The LTC2862A is protected from ±60V faults even with
the loss of GND or VCC (GND open faults not tested in
production). Additional precautions must be taken in the
case of VCC present and GND open. The LTC2862A chip
will protect itself from damage, but the chip ground current
may flow out through the ESD diodes on the logic I/O pins
and into associated circuitry. The system designer should
examine the susceptibility of the associated circuitry to
damage if the condition of a GND open fault with VCC
present is anticipated.
The high voltage rating of the LTC2862A makes it simple
to extend the overvoltage protection to higher levels using
external protection components. Compared to lower
voltage RS485 transceivers, external protection devices
with higher breakdown voltages can be used, so as not to
interfere with data transmission in the presence of large
common mode voltages. The Typical Applications section
shows a protection network against faults up to ±360V
peak, while still maintaining the extended ±25V common
mode range on the signal lines.
12
±40kV ESD Protection
The LTC2862A features exceptionally robust ESD
protection. The transceiver interface pins (A,B) feature
protection to ±40kV HBM with respect to GND, VCC (with a
1µF capacitor to GND), A or B without latchup or damage,
during all modes of operation or while unpowered. All
the other pins are protected to ±15kV HBM to make this
a component capable of reliable operation under severe
environmental conditions.
Level 4 IEC ESD and EFT Protection
The improved ESD protection of the LTC2862A provides a
high level of protection in the IEC ESD and EFT (Electrical
Fast Transient) tests. The IEC ESD stress exceeds that of
the HBM test in peak current, amplitude, and rise time,
while the EFT test provides a prolonged repetitive stress.
Combined with the HBM test, the IEC tests help ensure
that the LTC2862A is robust under a wide range of real
world hazards. The LTC2862A passes the following tests
on the A, B pins:
•
IEC 61000-4-2 Edition 2.0 2008-12 ESD Level 4: ±8kV
contact (A or B to GND, direct discharge to bus pins
with transceiver and protection circuit mounted on a
test card with a low impedance ground discharge path
from board GND to ESD gun return lead, per Figure 4
of the standard)
•
IEC 61000-4-4 Second Edition 2004-07 EFT Level 4:
±5kV (line to GND, 5kHz repetition rate, 15ms burst
duration, 60 second test duration, discharge coupled
to bus pins through 100pF capacitor per paragraph
7.3.2 of the standard)
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LTC2862A
Applications Information
Enhanced EOS Protection
The improved ESD protection of the LTC2862A also provides superior resistance to electrical overstress (EOS)
damage in the presence of large fault voltages applied from
low impedance faults. The LTC2862A employs thyristor
type ESD protection on the A, B pins. While thyristors have
the low on-state impedance and high robustness needed
to achieve the very high levels of ESD protection of the
LTC2862A, they have the disadvantage of snapping back
to a low voltage conduction state after they have been
triggered by an initial voltage that exceeds ~±80V. In the
presence of a high voltage, high current fault source, the
large resulting currents will blow the bond wires inside
the LTC2862A package, resulting in a failed chip.
The LTC2862A mitigates the probability of this type of failure
by establishing a very high trigger current in addition to a
higher trigger voltage. In order to trigger the ESD cell, the
fault must not only exceed the ~±80V trigger voltage, but
must be able to source ~±500mA at that voltage to initiate
the snapback of the ESD cell. This makes the LTC2862A
much less susceptible to snapback induced failures created
by high voltage noise spikes or voltage transients caused
by inductive overshoot when the A,B pins are shorted to a
fault voltage source. (The snapback characteristics of the
ESD protection are not tested during production.)
Driver
The driver provides full RS485/RS422 compatibility. When
enabled, if DI is high, A–B is positive. When the driver is
disabled, both transmitter outputs are high impedance,
and the impedance is dominated by the receiver input
resistance, RIN.
All devices also feature thermal shutdown protection that
disables the driver and receiver in case of excessive power
dissipation (see Note 4). (Thermal shutdown is not tested
during production.)
Full Failsafe Operation
When the absolute value of the differential voltage between
the A and B pins is greater than 200mV with the receiver
enabled, the state of RO will reflect the polarity of (A–B).
These parts have a failsafe feature that guarantees the
receiver output will be in a logic 1 state (the idle state) when
the inputs are shorted, left open, or terminated but not
driven. The delay allows normal data signals to transition
through the threshold region without being interpreted as
a failsafe condition. This failsafe feature is guaranteed to
work for inputs spanning the entire common mode range
of –25V to 25V.
Most competing devices achieve the failsafe function by a
simple negative offset of the input threshold voltage. This
causes the receiver to interpret a zero differential voltage
as a logic 1 state. The disadvantage of this approach is
the input offset can introduce duty cycle asymmetry at the
receiver output that becomes increasingly worse with low
input signal levels and slow input edge rates.
Other competing devices use internal biasing resistors to
create a positive bias at the receiver inputs in the absence
of an external signal. This type of failsafe biasing is
ineffective if the network lines are shorted, or if the network
is terminated but not driven by an active transmitter.
A, B
200mV/DIV
Driver Overvoltage and Overcurrent Protection
The driver outputs are protected from short circuits to any
voltage within the Absolute Maximum range of –60V to
60V. The maximum current in a fault condition is ±250mA.
The driver includes a progressive foldback current limiting
circuit that continuously reduces the driver current limit
with increasing output fault voltage. The fault current is
less than ±15mA for fault voltages over ±40V.
A–B
200mV/DIV
RO
1.6V/DIV
40ns/DIV
286A F08
Figure 9. Duty Cycle of Balanced Receiver with ±200mV
10Mbps Input Signal
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13
LTC2862A
Applications Information
The LTC2862A uses fully symmetric positive and negative
receiver thresholds VTH– and VTH+ (typically ±125mV) to
maintain good duty cycle symmetry at low signal levels. The
failsafe operation is performed with a window comparator
to determine when the differential input voltage falls above
the VTFS failsafe threshold (typically –75mV) but below
the VTH+ threshold. If this condition persists for more
than about 40ns for the LTC2862A-1 or 1.2µs for the
LTC2862A-2 the failsafe condition is asserted and the RO
pin is forced to the logic 1 state. This circuit provides full
failsafe operation and a large dynamic signal hysteresis of
~250mV between VTH– and VTH+ with no negative impact
to receiver duty cycle symmetry, as shown in Figure 9.
The input signal in Figure 9 was obtained by driving a
10Mbps RS485 signal through 1000 feet of cable, thereby
attenuating it to a ±200mV signal with slow rise and fall
times. Good duty cycle symmetry is observed at RO despite
the degraded input signal.
The failsafe circuit has been enhanced with noise filtering
to exit the failsafe state. In the absence of noise filtering, a
noise transient that momentarily forces the A-B differential
voltage below the VTH– receiver threshold will cause the
RO output to go low, which may be interpreted as a false
start character by the microcontroller. The LTC2862A
receiver reduces these false signals by low pass filtering
the signal to exit the failsafe state. The noise filtering in the
failsafe circuit of the LTC2862A-2 is much greater than in
the LTC2862A-1, commensurate with its lower data rate.
For example, the LTC2862A-1 exits the failsafe state when
a –1V differential pulse of about 3ns duration is applied,
while the LTC2862A-2 requires a –1V pulse of about 400ns
duration to exit the failsafe state. (The minimum pulse
widths to enter or exit the failsafe state are not tested in
production, but the underlying filtering is reflected in the
tFSN, tFSX, tFSNS, and tFSXS measurements).
Enhanced Receiver Noise Immunity
An additional benefit of the fully symmetric receiver
thresholds is enhanced receiver noise immunity. The
differential input signal must go above the positive
threshold to register as a logic 1 and go below the
negative threshold to register as a logic 0. This provides
14
a hysteresis of 250mV (typical) at the receiver inputs for
any valid data signal. (An invalid data condition such as
a DC sweep of the receiver inputs will produce a different
observed hysteresis due to the activation of the failsafe
circuit.) Competing devices that employ a negative offset
of the input threshold voltage generally have a much
smaller hysteresis and subsequently have lower receiver
noise immunity.
The LTC2862A-2 provides additional noise immunity
by adding low-pass filtering to the differential signal in
its receiver. Commensurate with its maximum data rate
of 250kbps, the LTC2862A-2 receiver attenuates high
frequency signals above approximately 660kHz. This lowpass filter removes high frequency noise transients that
might otherwise be interpreted as data. (High frequency
noise filtering is not tested in production, but the underlying
filtering is reflected in the tPLHR, tPHLR, tPLHRS, and tPHLRS
measurements).
RS485 Network Biasing
RS485 networks are usually biased with a resistive divider
to generate a differential voltage of ≥200mV on the data
lines, which establishes a logic 1 state (the idle state)
when all the transmitters on the network are disabled. The
values of the biasing resistors are not fixed, but 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 LTC2862A eliminates the
need for external network biasing resistors provided they
are used in a network of transceivers with similar internal
failsafe features. The LTC2862A transceivers will operate
correctly on biased, unbiased, or under-biased networks.
Hi-Z State
The receiver output is internally driven high (to VCC) or
low (to GND) with no external pull-up needed. When the
receiver is disabled the RO pin becomes Hi-Z with a 250k
pull-up resistor to VCC.
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LTC2862A
Applications Information
High Receiver Input Resistance
The bus receiver input load from A or B to GND is less than
one-seventh unit load, permitting a total of 224 receivers
per system without exceeding the RS485 receiver loading
specification. The input load of the receiver is unaffected by
enabling/disabling the receiver or by powering/unpowering
the part.
Supply Current
The unloaded static supply currents in these devices
are low — typically 1.1mA for non slew limited devices
and 3.5mA for slew limited devices. In applications
with resistively terminated cables, the supply current is
dominated by the driver load. For example, when using two
120Ω terminators with a differential driver output voltage
of 2V, the DC load current is 33mA, which is sourced by
the positive voltage supply. Power supply current increases
with toggling data due to capacitive loading and this term
can increase significantly at high data rates. A plot of
the supply current vs data rate is shown in the Typical
Performance Characteristics of this data sheet.
During fault conditions with a positive voltage larger than
the supply voltage applied to the transmitter pins, or during
transmitter operation with a high positive common mode
voltage, positive current of up to 80mA may flow from the
transmitter pins back to VCC. If the system power supply
or loading cannot sink this excess current, a 5.6V 1W
1N4734 Zener diode may be placed between VCC and GND
to prevent an overvoltage condition on VCC.
The LTC2862A contains a supply undervoltage lockout
circuit that enables the transmitter and receiver outputs
when VCC exceeds ~2.7V and disables the transmitter and
receiver outputs when VCC falls below ~2.5V.
When the LTC2862A is unpowered, the logic inputs (DE,
DI, RE) are high impedance for voltages > 0V. Each input
has a diode clamp to GND that will conduct if a negative
voltage sufficient to forward bias the diode (~ –0.6V at
25°C) is applied to the pad. The RO output contains a CMOS
driver with parasitic diodes to GND and VCC. The diode to
GND will conduct if forward biased by a negative voltage
below GND, while the diode to VCC will conduct if forward
biased by a positive voltage above VCC. If VCC is low, this
will result in the RO line being clamped to approximately
0.6V above VCC. The impedance of the logic inputs and the
RO output are not tested with the LTC2862A unpowered.
Shutdown Mode Delay
The LTC2862A features a low power shutdown mode
that is entered when both the driver and the receiver
are simultaneously disabled (pin DE low and RE high).
A shutdown mode delay of approximately 250ns (not
tested in production) is imposed after this state is received
before the chip enters shutdown. If either DE goes high
or RE goes low during this delay, the delay timer is reset
and the chip does not enter shutdown. This reduces the
chance of accidentally entering shutdown if DE and RE are
driven in parallel by a slowly changing signal or if DE and
RE are driven by two independent signals with a timing
skew between them.
This shutdown mode delay does not affect the outputs of
the transmitter and receiver, which start to switch to the
high impedance state upon the reception of their respective disable signals as defined by the parameters tSHDND
and tSHDNR. The shutdown mode delay affects only the
time when all the internal circuits that draw DC power
from VCC are turned off.
High Speed Considerations
A ground plane layout with a 0.1µF bypass capacitor placed
less than 7mm away from the VCC pin is recommended.
The PC board traces connected to signals A/B should be
symmetrical and as short as possible to maintain good
differential signal integrity. To minimize capacitive effects,
the differential signals should be separated by more than
the width of a trace and should not be routed on top of
each other if they are on different signal planes.
Care should be taken to route outputs away from any
sensitive inputs to reduce feedback effects that might
cause noise, jitter, or even oscillations.
The logic inputs have a typical hysteresis of 100mV to
provide noise immunity. Fast edges on the outputs can
cause glitches in the ground and power supplies which are
exacerbated by capacitive loading. If a logic input is held
near its threshold (typically VCC /2), a noise glitch from a
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15
LTC2862A
Applications Information
driver transition may exceed the hysteresis levels on the
logic and data input pins, causing an unintended state
change. This can be avoided by maintaining normal logic
levels on the pins and by slewing inputs faster than 1V/μs.
Good supply decoupling and proper driver termination
also reduce glitches caused by driver transitions.
The boundary at 20Mbps in Figure 10 represents the
guaranteed maximum operating rate of the LTC2862A-1.
The dashed vertical line at 10Mbps represents the specified
maximum data rate in the RS485 standard. This boundary
is not a limit, but reflects the maximum data rate that the
specification was written for.
RS485 Cable Length vs Data Rate
It should be emphasized that the plot in Figure 10 shows
a typical relation between maximum data rate and cable
length. Results with the LTC2862A will vary, depending on
cable properties such as conductor gauge, characteristic
impedance, insulation material, and solid versus stranded
conductors.
Many factors contribute to the maximum cable length
that can be used for RS485 or RS422 communication,
including driver transition times, receiver threshold, duty
cycle distortion, cable properties and data rate. A typical
curve of cable length versus maximum data rate is shown
in Figure 10. Various regions of this curve reflect different
performance limiting factors in data transmission.
At frequencies below 100kbps, the maximum cable length is
determined by DC resistance in the cable. In this example,
a cable longer than 4000ft will attenuate the signal at the
far end to less than what can be reliably detected by the
receiver.
For data rates above 100kbps the capacitive and inductive
properties of the cable begin to dominate this relationship.
The attenuation of the cable is frequency and length
dependent, resulting in increased rise and fall times at
the far end of the cable. At high data rates or long cable
lengths, these transition times become a significant part
of the signal bit time. Jitter and intersymbol interference
aggravate this so that the time window for capturing valid
data at the receiver becomes impossibly small.
Low EMI 250kbps Data Rate
The LTC2862A-2 features slew rate limited transmitters
for low electromagnetic interference (EMI) in sensitive
applications. The slew rate limit circuit maintains
consistent control of transmitter slew rates across voltage
and temperature to ensure low EMI under all operating
conditions. Figure 11 demonstrates the reduction in
high frequency content achieved by the 250kbps mode
compared to the 20Mbps mode.
The 250kbps mode has the added advantage of reducing
signal reflections in an unterminated network, and thereby increasing the length of a network that can be used
without termination. Using the rule of thumb that the rise
time of the transmitter should be greater than four times
the one-way delay of the signal, networks of up to 140
feet can be driven without termination.
20
A–B (NON SLEW LIMITED) (dB)
1k
100
LOW EMI
MODE
LTC2862A-2
RS485
STANDARD
SPEC
10
10k
100k
1M
10M
DATA RATE (bps)
100M
80
0
–20
40
–40
20
–60
0
–80
–20
–100
–120
16
–40
SLEW LIMITED
0
2
4
6
8
FREQUENCY (MHz)
10
–60
12
2862A F11
2862A F10
Figure 10. Cable Length vs Data Rate (RS485/RS422 Standard
Shown in Vertical Dashed Line)
60
NON SLEW LIMITED
A–B (SLEW LIMITED) (dB)
CABLE LENGTH (FT)
10k
Figure 11. High Frequency EMI Reduction of Slew Limited
250kbps Mode Compared to Non Slew Limited 20Mbps Mode
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LTC2862A
Applications Information
PROFIBUS Compatible Interface
PROFIBUS is an RS485-based field bus. In addition
to the specifications of TIA/EIA-485-A, the PROFIBUS
specification contains additional requirements for cables,
interconnects, line termination, and signal levels. The
following discussion applies to the PROFIBUS Type A cables
with associated connectors and termination. The Type A
cable is a twisted pair shielded cable with a characteristic
impedance of 135Ω to 165Ω and a loop resistance of
< 110Ω/km.
The LTC2862A RS485 transceiver may be used in
PROFIBUS compatible equipment if the following
considerations are implemented. (Please refer to the
schematic of the PROFIBUS Compatible Interface in the
Typical Applications Section.)
1. The polarity of the PROFIBUS signal is opposite to the
polarity convention used in this data sheet. The PROFIBUS B wire is driven by a non-inverted signal, while
the A wire is driven by an inverted signal. Therefore,
it is necessary to swap the output connections from
the transceiver. Pin A is connected to the PROFIBUS
B wire, and Pin B is connected to the PROFIBUS A
wire.
2. Each end of the PROFIBUS line is terminated with
a 220Ω resistor between B and A, a 390Ω pull-up
resistor between B and VCC, and a 390Ω pull-down
resistor between A and GND. This provides suitable
termination for the 150Ω twisted pair transmission
cable.
3. The peak to peak differential voltage VOD received at
the end of a 100m cable with the cable and terminations described above must be greater than 4V and
less than 7V. The LTC2862A produces signal levels
in excess of 7V when driving this network directly.
8.2Ω resistors may be inserted between the A and
B pins of the transceiver and the B and A pins of the
PROFIBUS cable to attenuate the transmitted signal
to meet the PROFIBUS upper limit of 7V while still
providing enough drive strength to meet the lower
limit of 4V.
4. The LTC2862A transceiver should be powered by a
5% tolerance 5V supply (4.75V to 5.25V) to ensure
that the PROFIBUS VOD tolerances are met.
Auxiliary Protection for 5kV Surge, 5kV EFT, and 30kV
IEC ESD
An interface transceiver used in an industrial setting may
be exposed to extremely high levels of electrical overstress
due to phenomena such as lightning surge, electrical fast
transient (EFT) from switching high current inductive loads,
and electrostatic discharge (ESD) from the discharge of
electrically charged personnel or equipment. Test methods
to evaluate immunity of electronic equipment to these
phenomena are defined in the IEC standards 61000-4-2,
61000-4-4, and 61000-4-5, which address ESD, EFT, and
surge, respectively. The transients produced by the EFT and
particularly the surge tests contain much more energy than
the ESD transients. The LTC2862A is designed for high
robustness against ESD, but the on-chip protection is not
able to absorb the energy associated with the 61000-4-5
surge transients. Therefore, a properly designed external
protection network is necessary to achieve a high level of
surge protection, and can also extend the ESD and EFT
performance of the LTC2862A to extremely high levels.
In addition to providing surge, EFT and ESD protection,
an external network should preserve or extend the ability
of the LTC2862A to withstand overvoltage faults, operate
over a wide common mode, and communicate at high
frequencies. In order to meet the first two requirements,
protection components with suitably high conduction
voltages must be chosen. A means to limit current must be
provided to prevent damage in case a secondary protection
device or the ESD cell on the LTC2862A fires and conducts.
The capacitance of these components must be kept low
in order to permit high frequency communication over a
network with multiple nodes. Meeting the requirements
for conducting very high energy electrical transients while
maintaining high hold-off voltages and low capacitance is
a considerable challenge.
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17
LTC2862A
Applications Information
A protection network shown in the Typical Applications
section (Network for IEC Level 4 Protection Against 5kV
Surge, 5kV EFT and 30kV IEC ESD Plus ±360V Overvoltage
Protection) meets this challenge. The network provides
the following protection:
•
IEC 61000-4-2 ESD Level 4: ±30kV contact, ±30kV
air (line to GND, direct discharge to bus pins with
transceiver and protection circuit mounted on a ground
referenced test card per Figure 4 of the standard)
•
IEC 61000-4-4 EFT Level 4: ±5kV (line to GND, 5kHz
repetition rate, 15ms burst duration, 60 second test
duration, discharge coupled to bus pins through 100pF
capacitor per paragraph 7.3.2 of the standard)
•
IEC 61000-4-5 Surge Level 4: ±5kV (line to GND, line to
line, 8/20µs waveform, each line coupled to generator
through 80Ω resistor per Figure 14 of the standard)
This protection circuit adds only ~8pF of capacitance per
line (line to GND), thereby providing an extremely high level
of protection without significant impact to the performance
of the LTC2862A transceivers at high data rates.
18
The gas discharge tubes (GDTs) provide the primary
protection against electrical surges. These devices
provide a very low impedance and high current carrying
capability when they fire, safely discharging the surge
current to GND. The transient blocking units (TBUs) are
solid state devices that switch from a low impedance pass
through state to a high impedance current limiting state
when a specified current level is reached. These devices
limit the current and power that can pass through to the
secondary protection. The secondary protection consists
of a bidirectional thyristor, which triggers above 35V to
protect the bus pins of the LTC2862A transceiver. The high
trigger voltage of the secondary protection maintains the
full ±25V common mode range of the receivers. The final
component of the network is the metal oxide varistors
(MOVs) which are used to clamp the voltage across the
TBUs to protect them against fast ESD and EFT transients
which exceed the turn-on time of the GDT.
The high performance of this network is attributable to
the low capacitance of the GDT and thyristor primary
and secondary protection devices. The high capacitance
MOV floats on the line and is shunted by the TBU, so it
contributes no appreciable capacitive load on the signal.
2862af
For more information www.linear.com/LTC2862A
LTC2862A
Typical Applications
PROFIBUS Compatible Line Interface
VCC
(4.75V TO 5.25V)
VCC
VCC
LTC2862A
RO
R
A*
8.2Ω
B*
8.2Ω
390Ω
B WIRE
100m
RE
DI
390Ω
B WIRE
220Ω
220Ω
VOD
A WIRE
5.5Ω/WIRE
D
390Ω
390Ω
A WIRE
DE
GND
4VP-P ≤ VOD ≤ 7VP-P UP TO 1500kbps
* THE POLARITY OF A AND B IN THIS DATA SHEET IS OPPOSITE THE POLARITY DEFINED BY PROFIBUS.
2862A TA02
±60V 20Mbps Level Shifter/Isolator
C
LTC2862A-1
VCC
DI
D
R2
A
DATA OUT 1
GND
B
C
GND
RO
R
R1
B
VCC1
VCC
R1
A
DATA IN 1
LTC2862A-1
VCC2
±60V
2862A TA03
R1 = 200k 1%. PLACE R1 RESISTORS NEAR A AND B PINS OF RECEIVER.
R2 = 10k
C = 47pF, 5%, 50 WVDC. MAY BE OMITTED FOR DATA RATES < 100kbps.
Failsafe O Application (Idle State = Logic O)
5V
LTC2862A
VCC
RO
I1
R
B
“A”
DE
DE
DI
RO
I2
DI
A
D
“B”
GND
2862A TA04
2862af
For more information www.linear.com/LTC2862A
19
LTC2862A
Package Description
Please refer to http://www.linear.com/product/LTC2862A#packaging for the most recent package drawings.
DD Package
8-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1698 Rev C)
0.70 ±0.05
3.5 ±0.05
1.65 ±0.05
2.10 ±0.05 (2 SIDES)
PACKAGE
OUTLINE
0.25 ± 0.05
0.50
BSC
2.38 ±0.05
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
PIN 1
TOP MARK
(NOTE 6)
0.200 REF
3.00 ±0.10
(4 SIDES)
R = 0.125
TYP
5
0.40 ± 0.10
8
1.65 ± 0.10
(2 SIDES)
0.75 ±0.05
4
0.25 ± 0.05
1
(DD8) DFN 0509 REV C
0.50 BSC
2.38 ±0.10
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-1)
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 TOP AND BOTTOM OF PACKAGE
20
2862af
For more information www.linear.com/LTC2862A
LTC2862A
Package Description
Please refer to http://www.linear.com/product/LTC2862A#packaging for the most recent package drawings.
S8 Package
S8 Package
8-Lead Plastic Small
Outline (Narrow .150 Inch)
8-Lead (Reference
Plastic Small
Outline
(NarrowRev
.150
LTC DWG
# 05-08-1610
G) Inch)
(Reference LTC DWG # 05-08-1610 Rev G)
.050 BSC
.189 – .197
(4.801 – 5.004)
NOTE 3
.045 ±.005
8
.245
MIN
.160 ±.005
5
.150 – .157
(3.810 – 3.988)
NOTE 3
1
RECOMMENDED SOLDER PAD LAYOUT
.010 – .020
× 45°
(0.254 – 0.508)
2
3
4
.053 – .069
(1.346 – 1.752)
.004 – .010
(0.101 – 0.254)
0°– 8° TYP
.016 – .050
(0.406 – 1.270)
NOTE:
1. DIMENSIONS IN
6
.228 – .244
(5.791 – 6.197)
.030 ±.005
TYP
.008 – .010
(0.203 – 0.254)
7
.014 – .019
(0.355 – 0.483)
TYP
INCHES
(MILLIMETERS)
2. DRAWING NOT TO SCALE
3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)
4. PIN 1 CAN BE BEVEL EDGE OR A DIMPLE
.050
(1.270)
BSC
SO8 REV G 0212
2862af
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 representaFor more ofinformation
tion that the interconnection
its circuits aswww.linear.com/LTC2862A
described herein will not infringe on existing patent rights.
21
LTC2862A
Typical Application
Network for IEC Level 4 Protection Against 5kV Surge, 5kV EFT
and 30kV IEC ESD Plus ±360V Overvoltage Protection
MOV
RS485 A
(EXTERNAL)
VCC
DE
TBU
GDT
LTC2862A-1
A
SCR
RO
R
GND
B
GDT
TBU
SCR
D
DI
RE
GND
RS485 B
(EXTERNAL)
2862A TA05
MOV
GDT: BOURNS 2031-42T-SM; 420V GAS DISCHARGE TUBE
TBU: BOURNS TBU-CA085-300-WH; 850V TRANSIENT BLOCKING UNIT
MOV: BOURNS MOV-7D391K; 390V 25J METAL OXIDE VARISTOR
SCR: BOURNS TISP4P035L1NR-S; 35V BIDIRECTIONAL THYRISTOR
Related Parts
PART NUMBER
DESCRIPTION
COMMENTS
LT1785, LT1791
±60V Fault Protected RS485/RS422 Transceivers
±60V Tolerant, ±15kV ESD, 250kbps
LTC2863/LTC2864/ ±60V Fault Protected 3V to 5.5V RS485/RS422 Transceivers
LTC2865
±60V Tolerant, ±15kV ESD, 20Mbps or 250kbps
LTC2877
±60V Rugged PROFIBUS RS485 Transceivers
PROFIBUS IEC 61158-2 Compliant, ±52kV ESD
LTM®2885
6500VRMS Isolated RS485/RS422 μModule® Transceiver + Power
6500VRMS for 1 Minute, Isolated Power: 5V at 150mA
LTC2850/LTC2851/ 3.3V 20Mbps ±15kV RS485 Transceivers
LTC2852
Up to 256 Transceivers Per Bus
LTC2854, LTC2855 3.3V 20Mbps RS485 Transceivers with Integrated Switchable Termination
±25kV ESD (LTC2854), ±15kV ESD (LTC2855)
LTC2856-1 Family
±15kV ESD
5V 20Mbps and Slew Rate Limited RS485 Transceivers
LTC2859, LTC2861 5V 20Mbps RS485 Transceivers with Integrated Switchable Termination
±15kV ESD
LTC1535
Isolated RS485 Transceiver
2500VRMS Isolation, Requires External Transceiver
LTM2881
Complete 3.3V Isolated RS485/RS422 μModule Transceiver + Power
2500VRMS Isolation with Integrated Isolated DC/DC
Converter, 1W Power, Low EMI, ±15kV ESD, 30kV/µs
Common Mode Transient Immunity
22
2862af
LT 0617 • PRINTED IN USA
For more information www.linear.com/LTC2862A
www.linear.com/LTC2862A
 LINEAR TECHNOLOGY CORPORATION 2017