_________________General Description
The MAX1480A/MAX1480B/MAX1480C/MAX1490A/
MAX1490B are complete, electrically isolated, RS-485/
RS-422 data-communications interface solutions in a
hybrid microcircuit. Transceivers, optocouplers, and a
transformer provide a complete interface in a standard
DIP package. A single +5V supply on the logic side pow-
ers both sides of the interface.
The MAX1480B/MAX1480C/MAX1490B feature reduced-
slew-rate drivers that minimize EMI and reduce reflec-
tions caused by improperly terminated cables, allowing
error-free data transmission at data rates up to 250kbps.
The MAX1480A/MAX1490A driver slew rate is not limited,
allowing transmission rates up to 2.5Mbps. The
MAX1480A/B/C are designed for half-duplex communi-
cation, while the MAX1490A/B feature full-duplex com-
munication.
Drivers are short-circuit current limited and protected
against excessive power dissipation by thermal shut-
down circuitry that places the driver outputs into a high-
impedance state. The receiver input has a fail-safe
feature that guarantees a known output (RO low for the
MAX1480A/B/C, RO high for the MAX1490A/B) if the
input is open circuit.
The MAX1480A/MAX1480B/MAX1480C/MAX1490A/
MAX1490B typically withstand 1600VRMS (1 minute) or
2000VRMS (1 second). Their isolated outputs meet all
RS-485/RS-422 specifications. The MAX1480A/B/C are
available in a 28-pin DIP package, and the MAX1490A/B
are available in a 24-pin DIP package.
________________________Applications
Isolated RS-485/RS-422 Data Interface
Transceivers for EMI-Sensitive Applications
Industrial-Control Local Area Networks
Automatic Test Equipment
HVAC/Building Control Networks
Next-Generation Device Features
♦♦For Integrated ESD Protection
MAX1480E/MAX1490E: ±15kV ESD-Protected,
Isolated RS-485/RS-422 Data Interfaces
♦♦For Space-Constrained Applications
MAX3157: High CMRR, RS-485 Transceiver with
±50V Isolation
MAX1480A/B/C/MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
________________________________________________________________
Maxim Integrated Products
1
124
23
22
21
20
19
18
17
2
3
4
5
6
7
8
AC1
AC2
ISO VCC1
ISO RO DRVD2
D1
A
B
Z
Y
SD
FS
GND1
16
15
14
13
9
10
11
12
ISO COM1
ISO DI DRV
ISO VCC2
ISO RO LED
GND2
RO
DI
DIP
VCC2
VCC3
VCC4
VCC1 MAX1490A/B
MAX845
MAX488
MAX490
TOP VIEW
ISOLATION BARRIER
Pin Configurations
19-0259; Rev 5; 5/05
_______________Ordering Information
Ordering Information continued at end of data sheet.
†
Data rate for “A” parts is up to 2.5Mbps. Data rate for “B” and
“C” parts is up to 250kbps.
Pin Configurations continued at end of data sheet.
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
PART†TEMP RANGE PIN-PACKAGE
MAX1480ACPI 0°C to +70°C
28 Wide Plastic DIP
MAX1480AEPI -40°C to +85°C
28 Wide Plastic DIP
_____________________Selection Table
PART
HALF/
FULL
DUPLEX
DATA
RATE
(MBPS)
SLEW-
RATE
LIMITED
DRIVER
ENABLE
TIME
(µs)
MAX1480A Half 2.5 No 0.2
MAX1480B Half 0.25 Yes 35
MAX1480C Half 0.25 Yes 0.5
MAX1490A Full 2.5 No —
MAX1490B Full 0.25 Yes —
Complete, Isolated RS-485/RS-422
Data Interface
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VCC_ = 5V ±10%, VFS = VCC_, TA= TMIN to TMAX, unless otherwise noted. Typical values are at VCC_ = 5V and TA= +25°C.) (Notes 1, 2)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
With Respect to GND_
Supply Voltage (VCC_)...........................................-0.3V to +6V
Control Input Voltage (SD, FS)...............-0.3V to (VCC_ + 0.3V)
Receiver Output Voltage (RO, RO)........-0.3V to (VCC_ + 0.3V)
Output Switch Voltage (D1, D2)........................................+12V
With Respect to ISO COM_
Control Input Voltage (ISO DE_ ) ....-0.3V to (ISO VCC_ + 0.3V)
Driver Input Voltage (ISO DI_ ) .......-0.3V to (ISO VCC_ + 0.3V)
Receiver Output Voltage (ISO RO_)
...-0.3V to (ISO VCC_ + 0.3V)
Driver Output Voltage (A, B, Y, Z ) ......................-8V to +12.5V
Receiver Input Voltage (A, B)..............................-8V to +12.5V
LED Forward Current (DI, DE, ISO RO LED) ......................50mA
Continuous Power Dissipation (TA= +70°C)
24-Pin Plastic DIP (derate 8.7mW°C above +70°C) .....696mW
28-Pin Plastic DIP (derate 9.09mW/°C above +70°C) ..727mW
Operating Temperature Ranges
MAX1480_CPI/MAX1490_CPG............................0°C to +70°C
MAX1480_EPI/MAX1490_EPG .........................-40°C to +85°C
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10s) .................................+300°C
MAX1480A/B/C/MAX1490A/B
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
fSWL VFS = 0V 535
Switch Frequency fSWH FS = VCC_ or open 725 kHz
RL = ∞, +25°C only 60 90
MAX1480A,
DE´ = VCC_ or open RL = 54Ω120
RL = ∞, +25°C only 35 45
MAX1480B,
DE´ = VCC_ or open RL = 54Ω95
RL = ∞, +25°C only 35 75
MAX1480C,
DE´ = VCC_ or open RL = 54Ω95
RL = ∞, +25°C only 100 150
MAX1490A RL = 54Ω170
RL = ∞, +25°C only 65 125
Operating Supply Current ICC
MAX1490B RL = 54Ω130
mA
Shutdown Supply Current
(Note 3) ISHDN SD = VCC_ 0.2 µA
VSDH High 2.4
Shutdown Input Threshold VSDL Low 0.8 V
Shutdown Input Leakage Current 10 pA
VFSH High 2.4
FS Input Threshold VFSL Low 0.8 V
FS Input Pullup Current FS low 50 µA
FS Input Leakage Current FS high 10 pA
Input High Voltage VIH DE´, DI´VCC_ - 0.4 V
Input Low Voltage VIL DE´, DI´0.4 V
Isolation Resistance RISO TA = +25°C, VISO = 50VDC 100 10,000 MΩ
Isolation Capacitance CISO TA = +25°C, VISO = 50VDC 10 pF
Differential Driver Output
(No Load) VOD1 8V
MAX1480A/B/C/MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
_______________________________________________________________________________________ 3
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
R = 50Ω (RS-422) 2
Differential Driver Output
(With Load) VOD2 R = 27Ω (RS-485), Figure 4 1.5 5.0 V
Differential 0.3
Change in Magnitude of
Differential Output Voltage for
Complementary Output States
ΔVOD R = 27Ω or 50Ω,
Figure 4 Common mode 0.3
V
Driver Common-Mode Output
Voltage VOC R = 27Ω or 50Ω, Figure 4 4 V
MAX1480A/B/C 1
VIN = 12V MAX1490A/B 0.25
MAX1480A/B/C 0.8
Input Current (A, B) ISO IIN
DE´ = 0V,
VCC_ = 0V
or 5.5V VIN = -7V MAX1490A/B 0.2
mA
MAX1480A/B/C 48
Receiver Input Resistance RIN -7V ≤ VCM ≤ 12V MAX1490A/B 12 kΩ
Receiver Differential Threshold
Voltage VTH -7V ≤ VCM ≤ 12V -0.2 +0.2 V
Receiver Input Hysteresis ΔVTH VCM = 0V 70 mV
Receiver Output/Receiver Output
Low Voltage VOL Using resistor values listed in
Tables 1 and 2 0.4 V
Receiver Output/Receiver Output
High Current IOH VOUT = 5.5V 250 µA
Driver Short-Circuit Current ISO IOSD -7V ≤ VO ≤ 12V (Note 4) 100 mA
ELECTRICAL CHARACTERISTICS (continued)
(VCC_ = 5V ±10%, VFS = VCC_, TA= TMIN to TMAX, unless otherwise noted. Typical values are at VCC_ = 5V and TA= +25°C.) (Notes 1, 2)
SWITCHING CHARACTERISTICS—MAX1480A/MAX1490A
(VCC_ = 5V ±10%, FS = VCC_, TA= TMIN to TMAX, unless otherwise noted. Typical values are at VCC_ = 5V and TA= +25°C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
tPLH 100 275
Driver Input to Output
Propagation Delay tPHL
Figures 5 and 7, RDIFF = 54Ω, CL1 = CL2
= 100pF 100 275 ns
Driver Output Skew tSKEW Figures 5 and 7, RDIFF = 54Ω, CL1 = CL2
= 100pF 25 90 ns
Driver Rise or Fall Time tR, tFFigures 5 and 7, RDIFF = 54Ω, CL1 = CL2
= 100pF 15 40 ns
Driver Enable to Output High
(MAX1480A Only) tZH Figures 6 and 8, CL = 100pF, S2 closed 0.2 1.5 µs
Driver Enable to Output Low
(MAX1480A Only) tZL Figures 6 and 8, CL = 100pF, S1 closed 0.2 1.5 µs
Driver Disable Time from Low
(MAX1480A Only) tLZ Figures 6 and 8, CL = 15pF, S1 closed 0.2 1.5 µs
Driver Disable Time from High
(MAX1480A Only) tHZ Figures 6 and 8, CL = 15pF, S2 closed 0.2 1.5 µs
tPLH 100 225
Receiver Input to Output
Propagation Delay tPHL
Figures 5 and 10, RDIFF = 54Ω, CL1 = CL2
= 100pF 100 225 ns
MAX1480A/B/C/MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
4 _______________________________________________________________________________________
SWITCHING CHARACTERISTICS—MAX1480A/MAX1490A (continued)
(VCC_ = 5V ±10%, FS = VCC_, TA= TMIN to TMAX, unless otherwise noted. Typical values are at VCC_ = 5V and TA= +25°C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
|tPLH - tPHL| Differential Receiver
Skew tSKD Figures 5 and 10, RDIFF = 54Ω, CL1 = CL2
= 100pF 20 ns
Maximum Data Rate fMAX tPLH, tPHL < 50% of data period 2.5 Mbps
Time to Shutdown tSHDN 100 µs
Shutdown to Driver Output High tZH
(
SHDN
)
Figures 6 and 9, CL = 100pF, S2 closed 3 10 µs
Shutdown to Driver Output Low tZL
(
SHDN
)
Figures 6 and 9, CL = 100pF, S1 closed 3 10 µs
SWITCHING CHARACTERISTICS—MAX1480B/MAX1480C/MAX1490B
(VCC_ = 5V ±10%, FS = VCC_, TA= TMIN to TMAX, unless otherwise noted. Typical values are at VCC_ = 5V and TA= +25°C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
tPLH 2 3.0
Driver Input to Output
Propagation Delay tPHL
Figures 5 and 7, RDIFF = 54Ω,
CL1 = CL2 = 100pF 2 3.0 µs
Driver Output Skew tSKEW Figures 5 and 7, RDIFF = 54Ω,
CL1 = CL2 = 100pF 900 1600 ns
Driver Rise or Fall Time tR, tFFigures 5 and 7, RDIFF = 54Ω,
CL1 = CL2 = 100pF 1.0 2.0 µs
Driver Enable to Output High
(MAX1480B Only) tZH Figures 6 and 8, CL = 100pF, S2 closed 35 100 µs
Driver Enable to Output Low
(MAX1480B Only) tZL Figures 6 and 8, CL = 100pF, S1 closed 35 100 µs
Driver Disable Time from Low
(MAX1480B Only) tLZ Figures 6 and 8, CL = 15pF, S1 closed 13 50 µs
Driver Disable Time from High
(MAX1480B Only) tHZ Figures 6 and 8, CL = 15pF, S2 closed 13 50 µs
Driver Enable to Output High
(MAX1480C Only) tZH Figures 6 and 8, CL = 100pF, S2 closed 0.5 4.5 µs
Driver Enable to Output Low
(MAX1480C Only) tZL Figures 6 and 8, CL = 100pF, S1 closed 0.5 4.5 µs
MAX1480A/B/C, MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
_______________________________________________________________________________________ 5
Note 1: All currents into device pins are positive; all currents out of device pins are negative. All voltages are referenced to logic-
side ground (GND_), unless otherwise specified.
Note 2: For DE´ and DI´pin descriptions, see
Detailed Block Diagram and Typical Application Circuit
(Figure 1 for MAX1480A/
MAX1480B/MAX1480C, Figure 2 for MAX1490A/MAX1490B).
Note 3: Shutdown supply current is the current at VCC1 and VCC2 when shutdown is enabled.
Note 4: Applies to peak current (see
Typical Operating Characteristics
). Although the MAX1480A/B/C and MAX1490A/B provide
electrical isolation between logic ground and signal paths, they do not provide isolation between external shields and the
signal paths (see
Isolated Common Connection
section).
SWITCHING CHARACTERISTICS—MAX1480B/MAX1480C/MAX1490B (continued)
(VCC_ = 5V ±10%, FS = VCC_, TA= TMIN to TMAX, unless otherwise noted. Typical values are at VCC_ = 5V and TA= +25°C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Driver Disable Time from Low
(MAX1480C Only) tLZ Figures 6 and 8, CL = 15pF, S1 closed 2.0 4.5 µs
Driver Disable Time from High
(MAX1480C Only) tHZ Figures 6 and 8, CL = 15pF, S2 closed 2.0 4.5 µs
tPLH 2 3.0
Receiver Input to Output
Propagation Delay tPHL
Figures 5 and 10, RDIFF = 54Ω,
CL1 = CL2 = 100pF 2 3.0 µs
|tPLH - tPHL| Differential Receiver
Skew tSKD Figures 5 and 10, RDIFF = 54Ω,
CL1 = CL2 = 100pF 1200 ns
Maximum Data Rate fMAX tPLH, tPHL < 50% of data period 0.25 Mbps
Time to Shutdown tSHDN 100 µs
Shutdown to Driver Output High tZH
(
SHDN
)
Figures 6 and 9, CL = 100pF, S2 closed 35 100 µs
Shutdown to Driver Output Low tZL
(
SHDN
)
Figures 6 and 9, CL = 100pF, S1 closed 35 100 µs
MAX1480A/B/C, MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
6 _______________________________________________________________________________________
0
OUTPUT CURRENT vs.
RECEIVER OUTPUT LOW VOLTAGE
MAX1480/90A/B-01
OUTPUT LOW VOLTAGE (V)
OUTPUT CURRENT (mA)
1.5
10
20
30
40
50
60
70
80 MEASURED AT ISO RO DRV
1.00.50 3.53.02.52.0 5.04.54.0
0
OUTPUT CURRENT vs.
RECEIVER OUTPUT HIGH VOLTAGE
MAX1480/90A/B-02
OUTPUT HIGH VOLTAGE (V)
OUTPUT CURRENT (mA)
1.5
-5
MEASURED AT ISO RO DRV
1.00.50 3.53.02.52.0 5.04.54.0
-10
-15
-20
-25
-30
3.00
-40 20
RECEIVER OUTPUT HIGH VOLTAGE
vs. TEMPERATURE
MAX1480/90A/B-03
TEMPERATURE (°C)
OUTPUT HIGH VOLTAGE (V)
0-20 6040 80
3.25
3.50
3.75
4.00
4.25
4.50
4.75
5.00 MEASURED AT ISO RO DRV
IRO = 8mA
0
-40 20
RECEIVER OUTPUT LOW VOLTAGE
vs. TEMPERATURE
MAX1480/90A/B-04
TEMPERATURE (°C)
OUTPUT LOW VOLTAGE (V)
0-20 6040 80
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8 MEASURED AT ISO RO DRV
IRO = 8mA
0
DRIVER OUTPUT CURRENT
vs. DIFFERENTIAL OUTPUT VOLTAGE
MAX1480/90A/B-07
DIFFERENTIAL OUTPUT VOLTAGE (V)
OUTPUT CURRENT (mA)
1.5
10
20
30
40
50
60
70
80
DI´ = HIGH OR OPEN
1.00.50 3.53.02.52.0 5.04.54.0
OUTPUT CURRENT vs.
DRIVER OUTPUT LOW VOLTAGE
MAX1480/90A/B-05
OUTPUT LOW VOLTAGE (V)
OUTPUT CURRENT (mA)
0
160
180
140
100
120
80
40
60
0
20
123456789101112
0
-7
OUTPUT CURRENT vs.
DRIVER OUTPUT HIGH VOLTAGE
MAX1480/90A/B-06
OUTPUT HIGH VOLTAGE (V)
OUTPUT CURRENT (mA)
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
-6 -5 -4 -3 -2 -1 1 2 3 4 5 6
2.0
-40 20
DRIVER DIFFERENTIAL OUTPUT VOLTAGE
vs. TEMPERATURE
MAX1480/90A/B-08
TEMPERATURE (°C)
DIFFERENTIAL OUTPUT VOLTAGE (V)
0-20 6040 80
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3.0
DI´ = HIGH OR OPEN
RL = 54Ω
0
-40 20
MAX1480B/MAX1480C/MAX1490B
SHUTDOWN CURRENT vs. TEMPERATURE
MAX1480/90A/B-09
TEMPERATURE (°C)
SHUTDOWN CURRENT (μA)
0-20 6040 80
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
SD = VCC_, DI´ = VCC_
DE´ (MAX1480B/C ONLY) = VCC_
MEASURED AT VCC1 AND VCC2
__________________________________________Typical Operating Characteristics
(VCC_ = 5V, FS = VCC_, TA = +25°C, unless otherwise noted.)
MAX1480A/B/C, MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
_______________________________________________________________________________________
7
_____________________________Typical Operating Characteristics (continued)
(VCC_ = 5V, FS = VCC_, TA = +25°C, unless otherwise noted.)
0
60
40
20
80
100
120
140
160
MAX1480A
SUPPLY CURRENT vs. TEMPERATURE
MAX1480/90A/B-10
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
-40 -20 0 20 40 60 80
VCC = 5.5V
VCC = 5.0V
VCC = 5.5V VCC = 5.0V
VCC = 4.5V
RL = 54Ω
RL = ∞
VCC = 4.5V
DE´ = VCC
20
60
40
80
100
120
140
MAX1480B
SUPPLY CURRENT vs. TEMPERATURE
MAX1480/90A/B-11
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
-40 -20 0 20 40 60 80
VCC = 5.5V
VCC = 5.0V
VCC = 5.5V VCC = 5.0V
RL = 54Ω
RL = ∞
DE´ = VCC
VCC = 4.5V
VCC = 4.5V
20
70
60
50
30
40
80
90
100
110
120
MAX1480C
SUPPLY CURRENT vs. TEMPERATURE
MAX1480/90A/B-12
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
-40 -20 0 20 40 60 80
VCC = 5.5V
VCC = 5.0V
VCC = 5.5V
VCC = 5.0V
VCC = 4.5V
RL = 54Ω
RL = ∞
VCC = 4.5V
DE´ = VCC
80
120
100
140
160
180
200
MAX1490A
SUPPLY CURRENT vs. TEMPERATURE
MAX1480/90A/B-13
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
-40 -20 0 20 40 60 80
VCC = 5.5V
VCC = 5.0V
VCC = 5.5V
VCC = 5.0V
VCC = 4.5V
RL = 54Ω
RL = ∞
VCC = 4.5V
50
100
90
80
60
70
110
120
130
140
150
MAX1490B
SUPPLY CURRENT vs. TEMPERATURE
MAX1480/90A/B-14
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
-40 -20 0 20 40 60 80
VCC = 5.5V
VCC = 5.0V
VCC = 5.5V
VCC = 5.0V
VCC = 4.5V
RL = 54Ω
RL = ∞
VCC = 4.5V
0.1
10
1
100
DRIVER ENABLE TIME
vs. TEMPERATURE
MAX1480/90A/B-15b
TEMPERATURE (°C)
DRIVER ENABLE TIME (μs)
-40 -20 0 20 40 60 80
MAX1480A
MAX1480C
MAX1480B
RL = 54Ω
VDI´ = 0V MEASURED FROM
DE´ TO VALID OUTPUT
MAX1480A/B/C, MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
8 _______________________________________________________________________________________
VCC_ = 5.0V, DI´= 0V
DE´ TOGGLED 0V TO 5V AT 5kHz
MAX1480B
DRIVER ENABLE TIME
DRIVER
OUTPUT B
2V/div
DE´
2V/div
10μs/div
MAX1480/90-17
VCC_ = 5.0V, DI´= 0V
DE´ TOGGLED 0V TO 5V AT 5kHz
MAX1480B
DRIVER DISABLE TIME
DE´
2V/div
5μs/div
DRIVER
OUTPUT B
2V/div
MAX1480/90-18
VCC_ = 5.0V, DI´= 0V
DE
´
TOGGLED 0V TO 5V AT 5kH
MAX1480C
DRIVER ENABLE TIME
DE´
2V/div
500ns/div
DRIVER
OUTPUT B
2V/div
MAX1480/90-25
VCC_ = 5.0V, DI´ = 0V
DE´ TOGGLED 0V TO 5V AT 5kHz
MAX1480C
DRIVER DISABLE TIME
DE´
2V/div
500ns/div
DRIVER
OUTPUT B
2V/div
MAX1480/90-26
VCC_ = 5.0V, DI´= 0V
DE´ TOGGLED 0V TO 5V AT 5kHz
MAX1480A
DRIVER ENABLE TIME
DE´
2V/div
200ns/div
DRIVER
OUTPUT B
2V/div
MAX1480/90-19
_____________________________Typical Operating Characteristics (continued)
(VCC_ = 5V, FS = VCC_, VDI´= 0V, DE´toggled 0V to 5V at 5kHz, TA = +25°C, unless otherwise noted.)
VCC_ = 5.0V, DI´ = 0V
DE´ TOGGLED 0V TO 5V AT 5kHz
MAX1480A
DRIVER DISABLE TIME
DE´
2V/div
200ns/div
DRIVER
OUTPUT B
2V/div
MAX1480/90-20
MAX1480A/B/C, MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
_______________________________________________________________________________________
9
_____________________________Typical Operating Characteristics (continued)
(VCC_ = 5V, FS = VCC_, DE´= VCC_, VDI´= 0V to 5V at 1.25MHz, TA = +25°C, unless otherwise noted.)
VCC_ = 5.0V, DE´= VCC_
DI´ = 0V TO 5V AT 1.25MHz
MAX1480A/MAX1490A
RECEIVER tPHL
RO/RO
2V/div
20ns/div
RECEIVER
INPUT A
1V/div
RECEIVER
INPUT B
1V/div
MAX1480/90-21
VCC_ = 5.0V, DE´= VCC_
DI´ = 0V TO 5V AT 1.25MHz
MAX1480A/MAX1490A
RECEIVER tPLH
RO/RO
2V/div
20ns/div
RECEIVER
INPUT B
1V/div
RECEIVER
INPUT A
1V/div
MAX1480/90-22
VCC_ = 5.0V, DE´= VCC_
DI´= 0V TO 5V AT 125kHz
MAX1480B/MAX1480C/MAX1490B
RECEIVER tPHL
RECEIVER
INPUT A
1V/div
RECEIVER
INPUT B
1V/div
RO/RO
2V/div
200ns/div
MAX1480/90-23
VCC_ = 5.0V, DE´= VCC_
DI´= 0V TO 5V AT 125kHz
MAX1480B/MAX1480C/MAX1490B
RECEIVER tPLH
RECEIVER
INPUT A
1V/div
RECEIVER
INPUT B
1V/div
RO/RO
2V/div
500ns/div
MAX1480/90-24
VDI´ = 0V
VSD = 5V TO 0V AT 1kHz
POWER-UP DELAY TO DRIVER OUTPUTS VALID
DRIVER
OUTPUT B
(Z FOR MAX1490)
2V/div
1μs/div
SD
2V/div
MAX1480/90-16
MAX1480A/B/C, MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
10 ______________________________________________________________________________________
________________________________________________________________Pin Description
Internal Connections. Leave these pins unconnected.3, 43, 4
Logic-Side (nonisolated side) +5V Supply Voltages1, 2, 8, 101, 2, 8, 10
FUNCTION
PIN
D1, D2
VCC1–VCC4
NAME
Shutdown Input. Ground for normal operation. When high, the power oscillator is
disabled.
77
Frequency Select Input. If FS = VCC_ or is open, switch frequency is high; if FS
= GND, switch frequency is low. For optimal performance and minimal supply
current, connect FS to VCC_ or leave unconnected.
66
Logic-Side Ground. Connect to GND2 (pin 12).55
SD
FS
GND1
Logic-Side (non-isolated side) +5V Supply Voltage—14
Receiver Output. If A > B by 200mV, RO will be low; if A < B by 200mV, RO will
be high. Open collector; must have pullup to VCC_ (Table 1 of Figure 1).
—13
Logic-Side Ground. Connect to GND1 (pin 5).1212
VCC5
RO
GND2
Receiver Output. If A > B by 200mV, RO will be high; if A < B by 200mV, RO
will be low. Open collector; must have pullup to VCC (Table 2 of Figure 2).
11—
Driver-Enable Input. The driver outputs, A and B, are enabled by bringing DE´
high. The driver outputs are high impedance when DE´is low. If the driver out-
puts are enabled, the device functions as a line driver. While the driver outputs
are high impedance, the device functions as a line receiver. Drives internal
LED cathode through a resistor (Table 1 of Figure 1).
—11
Driver Input. With DE´high (MAX1480A/B/C only), a low on DI´forces output A
low and output B high. Similarly, a high on DI´forces output A high and output
B low. Drives internal LED cathode through a resistor (Table 1 of Figure 1 for
MAX1480A/B/C, Table 2 of Figure 2 for MAX1490A/B).
99
RO
DE
DI
Isolated Driver-Input Drive. With DE´high (MAX1480A/B/C only), a low on DI´
forces output A low and output B high. Similarly, a high on DI´forces output A
high and output B low. Connect to ISO DI IN (on the MAX1480A/B/C only) for
normal operation. Open-collector output; connect a pullup resistor to ISO VCC_
(Table 1 of Figure 1 for MAX1480A/B/C; Table 2 of Figure 2 for MAX1490A/B).
1519
Isolated Supply Voltage. Connect to ISO VCC1 (pin 26 for MAX1480A/B/C, or
pin 22 for MAX1490A/B).
1418
Isolated Driver-Enable Drive. The driver outputs, A and B, are enabled by bring-
ing DE´high. The driver outputs are high impedance when DE´ is low. If the driv-
er outputs are enabled, the device functions as a line driver. While the driver
outputs are high impedance, the device functions as a line receiver. Open-
collector output; must have pullup to ISO VCC_ and be connected to ISO DE IN
for normal operation (Table 1 of Figure 1).
—17
ISO DI DRV
ISO VCC2
ISO DE DRV
Isolated Common. Connect to ISO COM1 (pin 20).—16
Isolated Receiver Output LED. Internal LED anode in MAX1480A/B/C and LED
cathode in MAX1490A/B. Connect to ISO RO DRV through a resistor (Table 1 of
Figure 1 for MAX1480A/B/C; Table 2 of Figure 2 for MAX1490A/B).
1315
Isolated Common. For MAX1480A/B/C, connect to ISO COM2 (pin 16)
(Figures 1 and 2).
1620 ISO COM1
ISO COM2
ISO RO LED
MAX1480A/B/C MAX1490A/B
PINS ON THE NON-ISOLATED SIDE
PINS ON THE ISOLATED RS-485/RS-422 SIDE
PINS ON THE NON-ISOLATED SIDE
PINS ON THE ISOLATED RS-485/RS-422 SIDE
MAX1480A/B/C, MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
______________________________________________________________________________________ 11
Detailed Description
The MAX1480A/MAX1480B/MAX1480C/MAX1490A/
MAX1490B are complete, electrically isolated, RS-485/
RS-422 data-communications interface solutions.
Transceivers, optocouplers, a power driver, and a
transformer in one standard 28-pin DIP package (24-
pin for the MAX1490A/B) provide a complete interface.
Signals and power are internally transported across the
isolation barrier (Figures 1, 2). Power is transferred from
the logic side (nonisolated side) to the isolated side of
the barrier through a center-tapped transformer.
Signals cross the barrier through high-speed optocou-
plers. A single +5V supply on the logic side powers
both sides of the interface. The MAX1480A/B/C offer
half-duplex communications while the MAX1490A/B
feature full-duplex communication. The functional
input/output relationships are shown in Tables 3–6.
The MAX1480B/MAX1480C/MAX1490B feature reduced-
slew-rate drivers that minimize EMI and reduce reflec-
tions caused by improperly terminated cables, allowing
error-free transmission at data rates up to 250kbps. The
MAX1480A/MAX1490A driver slew rate is not limited,
allowing transmission rates up to 2.5Mbps.
The MAX1480B/MAX1480C/MAX1490B shutdown feature
reduces supply current to as low as 0.2µA by using the
SD pin (see the
Low-Power Shutdown Mode
section).
Use the FS pin to select between high and low switching
frequencies for the isolated power driver. The driver
switches at the lower frequency 535kHz when FS is low,
and at the higher frequency 725kHz when FS is high. The
FS pin has a weak internal pull-up that switches the
device to the high-frequency mode when FS is left
unconnected. With FS high or open, no-load supply
current is reduced by approximately 4mA, and by up to
8mA when fully loaded. For optimal performance and
minimal supply current, connect FS to VCC_ or leave
unconnected.
Drivers are short-circuit current limited and are protect-
ed against excessive power dissipation by thermal
shutdown circuitry that puts the driver outputs into a
high-impedance state. The receiver input has a fail-safe
feature that guarantees a logic-high RO (logic-low RO)
output if the input is open circuit.
On the MAX1480A/B/C, the driver outputs are enabled
by bringing DE´high. Driver-enable times are typically
0.2µs for the MAX1480A, 35µs for the MAX1480B, and
0.5µs for the MAX1480C. Allow time for the devices to be
enabled before sending data (see the Driver Enable
Time vs. Temperature graph in the
Typical Operating
Characteristics
). When enabled, driver outputs function
as line drivers. Driver outputs are high impedance when
DE´is low. While outputs are high impedance, they func-
tion as line receivers.
___________________________________________________Pin Description (continued)
Note: For DE´and DI´pin descriptions, see
Detailed Block Diagram and Typical Application Circuit
(Figure 1 for MAX1480A/B/C,
Figure 2 for MAX1490A/B).
PIN
MAX1490A/B
MAX1480A/B/C
A
ISO RO DRV
B
23 —Noninverting Driver Output and Noninverting Receiver Input
24 21 Isolated Receiver-Output Drive. Connect to ISO RO LED through a resistor
(Table 1 of Figure 1 for MAX1480A/B/C, Table 2 of Figure 2 for MAX1490A/B).
25 —Inverting Driver Output and Inverting Receiver Input
ISO VCC1
AC2, AC1
26 22 Isolated Supply Voltage Source
27, 28 23, 24 Internal Connections. Leave these pins unconnected.
ISO DI IN22 —Isolated Driver Input. Connect to ISO DI DRV for normal operation.
Z— 18 Inverting Driver Output
B
A
ISO DE IN
—19 Inverting Receiver Input
—20 Noninverting Receiver Input
21 —Isolated Driver-Enable Input. Connect to ISO DE DRV for normal operation.
NAME FUNCTION
Y— 17 Noninverting Driver Output
PINS ON THE ISOLATED RS-485/RS-422 SIDE (continued)
MAX1480A/B/C, MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
12 ______________________________________________________________________________________
The MAX1480A/MAX1480B/MAX1480C/MAX1490A/
MAX1490B typically withstand 1600VRMS (1 minute) or
2000VRMS (1 second). The logic inputs can be driven
from TTL/CMOS-logic with a series resistor, and the
received data output can directly drive TTL or CMOS-
logic families with only resistive pullup.
Low-Power Shutdown Mode
The SD pin shuts down the oscillator on the internal power
driver. With the primary side in shutdown, no power is
transferred across the isolation barrier. The DI and DE
optocouplers, however, still consume current if the drive
signals on the nonisolated side are low. Therefore, leave
DI´and DE´high or floating when in shutdown mode.
AC1 (MAKE NO CONNECTION)
AC2 (MAKE NO CONNECTION)
SHIELD (OPTIONAL)
EXTERNAL RS-485/RS-422 WIRING
ISO VCC1
B
D2
D1
VCC2
VCC1
ISO RO DRV
A
B
A
SH
ISO DI IN
ISO DE IN
VCC3
SD
FS
GND1
ISO COM1
ISO DI DRV
ISO VCC2
ISO DE DRV
GND2
DE
VCC4
DI
ISO COM2
ISO RO LED
VCC5
RO
RL
RL
R4
R5
R7
100Ω
R1
R2
R3
R6
DE´
DI´
VIN
5V
22μF 0.1μF
C1 C2
MAX1480A/B/C
LOGIC GROUND ISOLATION BARRIER ISOLATED COMMON
DRIVER INPUT
DRIVER ENABLE
RECEIVER OUTPUT
DE
DI
RO
74HC86
OR EQUIVALENT
MAX1487
MAX487
MAX845
1
2
28
27
3
4
5
6
7
8
9
10
11
12
13
14
26
25
24
23
22
21
20
19
18
17
16
15
MAX845
NMAX1480A: MAX1487
MAX1480B: MAX487
MAX1480C: MAX487
RE
ISO RO DRV
ISO DE IN
ISO DI IN
ISO COM1
ISO VCC1
A
B
R
D
N
Q
Q
T F/F
VCC3
FS OSC
1.07MHz/
1.45MHz
SD GND1
D2
D1
SHIELD (OPTIONAL)
NOTE: RESISTOR R7 PROTECTS
THE MAX1480A/B/C FROM TRANSIENT
CURRENTS BETWEEN SHIELD AND
TRANSMISSION LINES.
TWISTED PAIR
TO OTHER TRANSCEIVERS
TERMINATING RESISTOR
(ONE RESISTOR ON EACH END)
TWISTED PAIR
TO OTHER TRANSCEIVERS
Figure 1. MAX1480A/MAX1480B/MAX1480C Detailed Block Diagram and Typical Application Circuit
200
510
R2 (Ω)
4300
2200
R4 (Ω)
1000
3000
R3 (Ω)
200
200
R6 (Ω)
1000
3000
R5 (Ω)
200MAX1480A
200MAX1480B
R1 (Ω)PART
Table 1. Pull-Up and LED Drive Resistors
200 30003000 2003000200MAX1480C
MAX1480A/B/C, MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
______________________________________________________________________________________ 13
Under these conditions, the MAX1480B/MAX1480C/
MAX1490B supply current is reduced to as low as 0.2µA.
The high-speed optocouplers on the MAX1480A/
MAX1480C/MAX1490A consume an additional 10mA
through VCC5 (VCC4 for the MAX1490A). Therefore, to
completely shut down these devices, use an external P-
channel MOSFET as shown in Figure 3. In normal opera-
tion, SD is low, turning the MOSFET on and thereby pro-
viding power to all the VCC_ pins. When SD is pulled high,
the power oscillator is disabled and the switch is turned
off, disconnecting power from the DI and DE optocou-
plers. In normal operating mode, the switch carries only
the optocoupler currents, so an on-resistance of several
ohms will not significantly degrade efficiency.
SHIELD (OPTIONAL)
EXTERNAL RS-485/RS-422 WIRING
A
RL
RL
B
Z
YRL
RL
R3
R4
R5, 100ΩSH1
SH2
R1
R2
R6, 100Ω
DI´
VIN
5V
22μF 0.1μF
C1 C2
MAX1490A/B
LOGIC GROUND
ISOLATION BARRIER ISOLATED COMMON
DRIVER INPUT
RECEIVER OUTPUT
DI
RO
74HC86
OR EQUIVALENT
MAX845
N
MAX1490A: MAX490
MAX1490B: MAX488
ISO DI DRV
ISO RO DRV
A
B
Z
Y
D
R
N
Q
Q
T F/F
VCC3
FS
OSC
1.07MHz/
1.45MHz
SD GND1
D2
D1
SHIELD (OPTIONAL)
NOTE: RESISTORS R5 AND R6 PROTECT
THE MAX1490A/B FROM TRANSIENT
CURRENTS BETWEEN SHIELD AND
TRANSMISSION LINES.
TWISTED PAIR
TO OTHER TRANSCEIVERS
TERMINATING RESISTOR
(ONE RESISTOR ON EACH END)
TWISTED PAIR
TO OTHER TRANSCEIVERS
24
23
22
21
20
19
18
17
1
2
3
4
5
6
7
8
AC1 (MAKE NO CONNECTION)
AC2 (MAKE NO CONNECTION)
ISO VCC1
ISO RO DRV
D2
D1
VCC2
VCC1
A
B
Z
Y
VCC3
SD
FS
GND1
16
15
14
13
9
10
11
12
ISO COM1
ISO DI DRV
ISO VCC2
ISO RO LED
GND2
R0
VCC4
DI
MAX845
MAX488
MAX490
Figure 2. MAX1490A/MAX1490B Detailed Block Diagram and Typical Application Circuit
Table 2. Pull-Up and LED Drive Resistors
1000
3000
R2 (Ω)
1000
3000
R4 (Ω)
330
330
R3 (Ω)
200MAX1490A
200MAX1490B
R1 (Ω)PART
MAX1480A/B/C, MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
14 ______________________________________________________________________________________
Figure 4. Driver DC Test Load
R
R
VOD
VOC
D
Figure 5. Driver/Receiver Timing Test Circuit
DI´
CL1
(DE´)
CL2
RO (RO)*
RDIFF
VID
ISOLATION BARRIER
( ) ARE FOR
THE MAX1480A/B/C
* OPTOCOUPLER
OUTPUTS. SEE FIGURES 1
AND 2 FOR DETAILED BLOCK
DIAGRAM AND TYPICAL
APPLICATION CIRCUIT.
ISOLATION BARRIER
RD
Test Circuits
28
27
26
25
24
23
22
21
1
2
3
4
5
6
7
8
AC1VIN
5V
SHUTDOWN
Si943304
DI
GND
DE
R1
R2
R3
P
RO
AC2
ISO VCC1
B
D2
D1
VCC2
VCC1
ISO RO DRV
A
ISO DI IN
ISO DE IN
VCC3
SD
FS
GND1
20
19
18
17
9
10
11
12
ISO COM1
ISO DI DRV
ISO VCC2
ISO DE DRV
GND2
DE
VCC4
DI
16
15
13
14
ISO COM2
ISO RO LED
VCC5
RO
MAX1487MAX845
ISOLATION BARRIER
MAX1480A
Figure 3. MAX1480A Low-Power Shutdown Mode
MAX1480A/B/C, MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
______________________________________________________________________________________ 15
Figure 6. Driver Timing Test Load
OUTPUT
UNDER TEST
500ΩS1
S2
ISO VCC_
CL
Figure 7. Driver Propagation Delays and Transition Times
DI´0V
B
A
VO
0V
-VO
VO
tPLH
1/2 VO
10%
tR
90% 90%
tPHL 1/2 VO
10%
tF
VDIFF = V (A) - V (B)
VDIFF
VCC_ - 0.4V
VCC_ - 0.4V
2
tSKEW = ⎢tPLH - tPHL ⎢
VCC_ - 0.4V
2
Figure 8. Driver Enable and Disable Times
OUTPUT NORMALLY LOW
OUTPUT NORMALLY HIGH
0V
A, B
VOL
A, B
0V
VOL + 0.5V
VCC_ - 0.4V
2
VCC_ - 0.4V
2
VCC_ -0.4V
VOH - 0.5V
2.3V
2.3V
tZL tLZ
tZH tHZ
DE´
Figure 9. Times to/from Shutdown
OUTPUT NORMALLY LOW
OUTPUT NORMALLY HIGH
2.4V
0.8V
A, B
VOL
A, B
0V
1.6V 1.6V
VOL + 0.5V
VOH - 0.5V
2.3V
2.3V
tZL(SHDN) tSHDN
tZH(SHDN) tSHDN
SD
Figure 10. Receiver Propagation Delays
VOH
VOL
-VID
VID
1.5V
0V
1.5V
1.5V 1.5V
MAX1480A/B/C
OUTPUT
MAX1490A/B
OUTPUT
INPUT
0V
RO
RO VOH
VOL
VA - VB
tPHL tPLH
tPLH
tPHL
tSKEW = ⏐tPLH - tPHL⏐
Switching Waveforms
____________________________________________________Test Circuits (continued)
MAX1480A/B/C, MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
16 ______________________________________________________________________________________
MAX1480B/MAX1480C/MAX1490B:
Reduced EMI and Reflections
The MAX1480B/MAX1480C/MAX1490B are slew-rate-
limited, minimizing EMI and reducing reflections
caused by improperly terminated cables. Figure 11
shows both the driver output waveform of a
MAX1480A/MAX1490A transmitting a 150kHz signal
and the Fourier analysis of that waveform. High-fre-
quency harmonics with large amplitudes are evident.
Figure 12 shows the same information for the slew-rate-
limited MAX1480B/MAX1480C/MAX1490B transmitting
the same signal. The high-frequency harmonics have
much lower amplitudes, and therefore the potential for
EMI is significantly reduced.
Table 3. Transmitting
Table 4. Receiving
Table 5. Transmitting
Table 6. Receiving
1
X
INPUTS*
1
High-Z
OUTPUTS
0
High-Z
1
0
Figure 11. Driver Output Waveform and FFT Plot of
MAX1480A/MAX1490A Transmitting a 150kHz Signal
10dB/div
0Hz 5MHz
500kHz/div
Figure 12. Driver Output Waveform and FFT Plot of
MAX1480B/MAX1480C/MAX1490B Transmitting a 150kHz
Signal
10dB/div
0Hz 5MHz
500kHz/div
_____________________Function Tables
Half-Duplex Devices
(MAX1480A/MAX1480B/MAX1480C)
Full-Duplex Devices
(MAX1490A/MAX1490B)
DI´AB
DE´
0 011
≥+0.2V
Open
INPUTS*
0
0
VA- VB
OUTPUT
(RO)
DE´
≤-0.2V 10
0
0
0 1
Z Y
1 00
1
1
1
OUTPUT
(RO)
0≤-0.2V
≥+0.2V
Open
INPUT
(VA- VB)
X = Don’t care
High-Z = High impedance
*
For DE´ and DI´ pin descriptions, see Detailed Block Diagram
and Typical Application Circuit (Figure 1 for MAX1480A/B/C,
Figure 2 for MAX1490A/B).
OUTPUTS
INPUT*
(DI´)
MAX1480A/B/C, MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
______________________________________________________________________________________ 17
DI
100Ω
DE
RO
BA
R
D
RE
RO
DE
DI
R
120ΩD
A
B
RERE
DI
DE
RO
BA
R
D
AC1 (MAKE NO CONNECTION)
AC2 (MAKE NO CONNECTION)
SHIELD
(OPTIONAL)
NOTE: RESISTOR R7 PROTECTS
THE MAX1480A/B/C FROM
TRANSIENT CURRENTS
BETWEEN SHIELD AND
TRANSMISSION LINES.
ISO VCC1
B
D2
D1
VCC2
VCC1
ISO RO DRV
A
B
A
SH
ISO DI IN
ISO DE IN
VCC3
SD
FS
GND1
ISO COM1
ISO DI DRV
ISO VCC2
ISO DE DRV
GND2
DE
VCC4
DI
ISO COM2
ISO RO LED
VCC5
RO
R4
R5
R7
100Ω
120Ω
R1
R2
R3
R6
VIN
5V
22μF 0.1μF
C1 C2
MAX1480A/B/C
LOGIC GROUND ISOLATION BARRIER ISOLATED COMMON
TERMINATING RESISTOR
(ONE RESISTOR ON EACH END)
DRIVER INPUT
DRIVER ENABLE
RECEIVER OUTPUT
DE
DI
RO
74HC86
OR EQUIVALENT
MAX487
MAX1487
MAX845
1
2
28
27
3
4
5
6
7
8
9
10
11
12
13
14
26
25
24
23
22
21
20
19
18
17
16
15
TERMINATING RESISTOR
(ONE RESISTOR ON EACH END)
Figure 13. Typical Half-Duplex RS-485/RS-422 Network
MAX1480A/B/C, MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
18 ______________________________________________________________________________________
Driver Output Protection
There are two mechanisms to prevent excessive output
current and power dissipation caused by faults or by
bus contention. A foldback current limit on the output
stage provides immediate protection against short cir-
cuits over the entire common-mode range (see the
Typical Operating Characteristics
). In addition, a ther-
mal shutdown circuit forces the driver outputs into a
high-impedance state if the die temperature rises
excessively.
Propagation Delay Skew
Typical propagation delays are shown in the
Typical
Operating Characteristics
using the test circuit of
Figure 5. Propagation delay skew is simply the differ-
ence between the low-to-high and high-to-low propaga-
tion delay. Small driver/receiver skew times help
reduce EMI and reflections by maintaining balanced
differential signals.
The receiver skew time, I tPLH - tPHL I, is typically under
100ns for the MAX1480A/MAX1490A and under 1µs for
the MAX1480B/MAX1480C/MAX1490B.
The driver skew time is typically 25ns for the
MAX1480A/MAX1490A and 100ns for the MAX1480B/
MAX1480C/MAX1490B.
___________Applications Information
DI and DE are intended to be driven through a
series current-limiting resistor. Directly grounding
these pins destroys the device.
The MAX1480A/MAX1480B/MAX1480C are designed
for bidirectional data communications on multipoint
bus-transmission lines. The MAX1490A/MAX1490B are
designed for full-duplex bidirectional communications
that are primarily point-to-point. Figures 13 and 14
show half-duplex and full-duplex typical network appli-
cation circuits, respectively. To minimize reflections,
terminate the line at both ends with its characteristic
impedance, and keep stub lengths off the main line as
short as possible. The slew-rate-limited MAX1480B/
MAX1480C/MAX1490B are more tolerant of imperfect
termination and stubs off the main line.
Layout Considerations
The MAX1480A/MAX1480B/MAX1480C/MAX1490A/
MAX1490B pinouts enable optimal PC board layout by
minimizing interconnect lengths and crossovers.
•For maximum isolation, the “isolation barrier” should
not be breached except by the MAX1480A/
MAX1480B/MAX1480C/MAX1490A/MAX1490B.
SHIELD (OPTIONAL)
NOTE: RESISTORS R5 AND R6 PROTECT
THE MAX1490A/B FROM TRANSIENT
CURRENTS BETWEEN SHIELD AND
TRANSMISSION LINES.
120Ω
120Ω
120Ω
A
B
Z
Y
Y
Z
R3
R4
R5, 100Ω
SH1
SH2
R1
R2
R6, 100Ω
DI´
VIN
5V
22μF 0.1μF
C1 C2
MAX1490A/B
LOGIC GROUND
ISOLATION BARRIER ISOLATED COMMON
DRIVER INPUT
RECEIVER OUTPUT
DI
RO
74HC86
OR EQUIVALENT
SHIELD (OPTIONAL)
24
23
22
21
20
19
18
17
1
2
3
4
5
6
7
8
AC1 (MAKE NO CONNECTION)
AC2 (MAKE NO CONNECTION)
ISO VCC1
ISO RO DRV
D2
D1
VCC2
VCC1
A
B
Z
Y
VCC3
SD
FS
GND1
16
15
14
13
9
10
11
12
ISO COM1
ISO DI DRV
ISO VCC2
ISO RO LED
GND2
RO
VCC4
DI
MAX845
MAX488
MAX490
DDI
RO
120Ω
B
A
R
Figure 14. Typical Full-Duplex RS-485/RS-422 Network
MAX1480A/B/C, MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
______________________________________________________________________________________ 19
Connections and components from one side should
not be located near those of the other side.
•A shield trace connected to the ground on each side
of the barrier can help intercept capacitive currents
that might otherwise couple into the signal path. In a
double-sided or multilayer board, these shield traces
should be present on all conductor layers.
•Try to maximize the width of the isolation barrier
wherever possible; a clear space of at least 0.25
inches between ground and isolated common is
suggested.
Pullup and LED Drive Resistors
The MAX1480A/MAX1480B/MAX1480C/MAX1490A/
MAX1490B are specified and characterized using the
resistor values shown in Table 1 of Figure 1 and Table
2 of Figure 2. Altering the recommended values can
degrade performance.
The DI and DE (MAX1480A/B/C only) inputs are the
cathodes of LEDs whose anodes are connected to the
supply. These points are best driven by a CMOS-logic
gate with a series resistor to limit the current. The resis-
tor values shown in Tables 1 and 2 are recommended
when the 74HC86 gate or equivalent is used. These
values may need to be adjusted if a driving gate with
dissimilar series resistance is used.
All pull-up resistors are based on optocoupler specifica-
tions in order to optimize the devices’ data-transfer rates.
Isolated Common Connection
The isolated common may be completely floating with
respect to the logic ground and the effective network
ground. The receiver input resistors will cause the iso-
lated common voltage to go to the mean voltage of the
receiver inputs. If using shielded cable, connect the
isolated common to the shield through a 100Ωresistor.
In the case of the MAX1490, each shield should have
its own 100Ωresistor (Figures 1, 2, 13, and 14).
28
3kΩ
3kΩ3kΩ
5712 5712
11
23 13 1
3kΩ
2
43 13
3kΩ
74HC04
200Ω9
25 25
23
26
A
B
A
B
19 9200Ω
200Ω
DRIVER
ENABLE
B > A 200Ω
74HC123
CLR
4
AQ
311
1
DRIVER
ENABLE
A > B
11
22
17
200Ω
15
21
24 24
10 14
NETWORK SEGMENT A NETWORK SEGMENT B
2 8 10 14
CLR
74HC123
12AQ9
3kΩ
26
19
22
17
200Ω
15
21
1000pF51kΩ
+5V
+5V +5V
+5V
51kΩ
16 15 14
13
2B Q
1000pF
76
5
10 BQ
MAX1480C MAX1480C
Figure 15. Doubly Isolated RS-485 Repeater
MAX1480A/B/C, MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
20 ______________________________________________________________________________________
Doubly Isolated RS-485 Repeater
The RS-422/RS-485 standard is specified for cable
lengths up to 4000 feet. When approaching or exceed-
ing the specified maximum cable length, a ground-
potential difference of several tens of volts can easily
develop. This difference can be either DC, AC, at
power-line frequency, or any imaginable noise or
impulse waveform. It is typically very low impedance so
that if a connection between the two grounds is
attempted, very large currents may flow. These cur-
rents are by their nature unstable and unpredictable. In
addition, they may cause noise to be injected into sen-
sitive instrumentation and, in severe cases, might actu-
ally cause physical damage to such equipment.
Figure 15 shows a half-duplex (two-wire), bidirectional,
party-line repeater system that prevents interference
and/or damage from ground-potential differences. Two
MAX1480A/MAX1480B/MAX1480C isolated RS-485
transceivers are used to isolate each of the network
segments from the electrical environment of the
repeater. The MAX1480A/MAX1480B/MAX1480C also
regenerate bus signals that may have been degraded
by line attenuation or dispersion.
In the idle state, both transmitters are disabled, while all
receivers in the system are enabled. If any device on
the system has information for any other device, it starts
sending its data onto the bus. Each data transmission
on the bus retriggers the one-shot, keeping the sending
transmitter enabled until there are no more transmis-
sions. All receivers receive all data; if this is undesir-
able, the protocol must allow for an address field so
receivers can ignore data not directed to them.
Each node must refrain from transmitting when data
already exists on the bus, and must resend data that is
corrupted by the collisions that inevitably occur with a
party-line system. With the repeater of Figure 15, there
might be transmitters up to 8000 feet apart. That repre-
sents more than 8µs (assuming 1ns/foot of delay) in
which two nodes could be transmitting simultaneously.
The circuit in Figure 15 can be used either directly as
shown, with the slew-rate-limited MAX1480B/MAX1480C,
for data transfer rates up to 250kbps, or with the
MAX1480A for data rates up to 2.5Mbps (see Table 1
for pullup and LED resistor values when using the
MAX1480A, MAX1480B, or MAX1480C). If dual-port iso-
lation is not needed, one of the MAX1480C devices can
be replaced by a MAX487 for 250kbps applications.
MAX1480A/B/C, MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________
21
© 2005 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.
Ordering Information (continued)Pin Configurations (continued)
28
27
26
25
24
23
22
21
1
2
3
4
5
6
7
8
AC1
AC2
ISO VCC1
B
D2
D1
VCC2
VCC1
ISO RO DRV
A
ISO DI IN
ISO DE IN
VCC3
SD
FS
GND1
20
19
18
17
9
10
11
12
ISO COM1
ISO DI DRV
ISO VCC2
ISO DE DRV
GND2
DE
VCC4
DI
16
15
13
14
ISO COM2
ISO RO LED
VCC5
RO
MAX487
MAX1487
MAX845
ISOLATION BARRIER
DIP
TOP VIEW
MAX1480A/B/C
†
Data rate for “A” parts is up to 2.5Mbps. Data rate for “B” and
“C” parts is up to 250kbps.
PART†TEMP RANGE PIN-PACKAGE
MAX1480BCPI 0°C to +70°C 28 Wide Plastic DIP
MAX1480BEPI -40°C to +85°C 28 Wide Plastic DIP
MAX1480CCPI 0°C to +70°C 28 Wide Plastic DIP
MAX1480CEPI -40°C to +85°C 28 Wide Plastic DIP
MAX1490ACPG 0°C to +70°C 24 Wide Plastic DIP
MAX1490AEPG -40°C to +85°C 24 Wide Plastic DIP
MAX1490BCPG 0°C to +70°C 24 Wide Plastic DIP
MAX1490BEPG -40°C to +85°C 24 Wide Plastic DIP
PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
28 PDIP P28M-1 21-0044
Package Information
For the latest package outline information and land patterns,
go to www.maxim-ic.com/packages. Note that a “+”, “#”, or
“-” in the package code indicates RoHS status only. Package
drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.