19-0259; Rev 5; 5/05
Complete, Isolated RS-485/RS-422
Data Interface
Next-Generation Device Features
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 powers both sides of the interface.
♦ 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
The MAX1480B/MAX1480C/MAX1490B feature reducedslew-rate drivers that minimize EMI and reduce reflections 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 communication, while the MAX1490A/B feature full-duplex communication.
Drivers are short-circuit current limited and protected
against excessive power dissipation by thermal shutdown circuitry that places the driver outputs into a highimpedance 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
_______________Ordering Information
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
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.
_____________________Selection Table
PART
HALF/
FULL
DUPLEX
DATA
RATE
(MBPS)
SLEWRATE
LIMITED
DRIVER
ENABLE
TIME
(µs)
0.2
MAX1480A
Half
2.5
No
MAX1480B
Half
0.25
Yes
35
MAX1480C
Half
0.25
Yes
0.5
MAX1490A
Full
2.5
No
—
MAX1490B
Full
0.25
Yes
—
Pin Configurations
TOP VIEW
Isolated RS-485/RS-422 Data Interface
VCC1
1
Transceivers for EMI-Sensitive Applications
VCC2
2
23 AC2
Industrial-Control Local Area Networks
D1
3
22 ISO VCC1
Automatic Test Equipment
D2
4
21 ISO RO DRV
GND1
5
20 A
MAX488
MAX490
FS 6
MAX845
HVAC/Building Control Networks
24 AC1
MAX1490A/B
19 B
SD
7
18 Z
VCC3
8
17 Y
DI
9
16 ISO COM1
VCC4 10
15 ISO DI DRV
14 ISO VCC2
RO 11
13 ISO RO LED
GND2 12
ISOLATION BARRIER
DIP
Pin Configurations continued at end of data sheet.
________________________________________________________________ Maxim Integrated Products
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.
1
MAX1480A/B/C/MAX1490A/B
_________________General Description
MAX1480A/B/C/MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
ABSOLUTE MAXIMUM RATINGS
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
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.
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)
PARAMETER
Switch Frequency
Operating Supply Current
SYMBOL
CONDITIONS
535
fSWH
FS = VCC_ or open
725
ICC
MAX1480A,
DE´ = VCC_ or open
RL = ∞, +25°C only
60
RL = 54Ω
120
MAX1480B,
DE´ = VCC_ or open
RL = ∞, +25°C only
35
RL = 54Ω
95
RL = ∞, +25°C only
35
RL = 54Ω
95
RL = ∞, +25°C only
100
RL = 54Ω
170
MAX1480C,
DE´ = VCC_ or open
MAX1490B
Shutdown Input Threshold
ISHDN
SD = VCC_
VSDH
High
VSDL
Low
VFSH
High
VFSL
Low
RL = ∞, +25°C only
65
RL = 54Ω
130
FS low
FS Input Leakage Current
FS high
Input High Voltage
VIH
DE´, DI´
Input Low Voltage
VIL
DE´, DI´
Isolation Resistance
RISO
TA = +25°C, VISO = 50VDC
90
45
75
Isolation Capacitance
CISO
TA = +25°C, VISO = 50VDC
Differential Driver Output
(No Load)
VOD1
mA
150
125
µA
2.4
0.8
V
pA
2.4
0.8
50
10
V
µA
pA
VCC_ - 0.4
V
0.4
100
UNITS
kHz
10
FS Input Pullup Current
2
MAX
0.2
Shutdown Input Leakage Current
FS Input Threshold
TYP
VFS = 0V
MAX1490A
Shutdown Supply Current
(Note 3)
MIN
fSWL
V
10,000
MΩ
10
pF
_______________________________________________________________________________________
8
V
Complete, Isolated RS-485/RS-422
Data Interface
(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)
PARAMETER
SYMBOL
Differential Driver Output
(With Load)
VOD2
Change in Magnitude of
Differential Output Voltage for
Complementary Output States
ΔVOD
Driver Common-Mode Output
Voltage
VOC
Input Current (A, B)
ISO IIN
CONDITIONS
R = 50Ω (RS-422)
DE´ = 0V,
VCC_ = 0V
or 5.5V
VIN = 12V
VIN = -7V
RIN
-7V ≤ VCM ≤ 12V
Receiver Differential Threshold
Voltage
VTH
-7V ≤ VCM ≤ 12V
Receiver Output/Receiver Output
Low Voltage
Receiver Output/Receiver Output
High Current
Driver Short-Circuit Current
ΔVTH
1.5
MAX
5.0
Differential
0.3
Common mode
0.3
UNITS
V
V
R = 27Ω or 50Ω, Figure 4
Receiver Input Resistance
Receiver Input Hysteresis
TYP
2
R = 27Ω (RS-485), Figure 4
R = 27Ω or 50Ω,
Figure 4
MIN
4
MAX1480A/B/C
V
1
MAX1490A/B
0.25
MAX1480A/B/C
0.8
MAX1490A/B
mA
0.2
MAX1480A/B/C
48
MAX1490A/B
12
kΩ
-0.2
VCM = 0V
+0.2
70
V
mV
VOL
Using resistor values listed in
Tables 1 and 2
0.4
V
IOH
VOUT = 5.5V
250
µA
ISO IOSD
-7V ≤ VO ≤ 12V (Note 4)
100
mA
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
Driver Input to Output
Propagation Delay
SYMBOL
tPLH
tPHL
CONDITIONS
Figures 5 and 7, RDIFF = 54Ω, CL1 = CL2
= 100pF
MIN
TYP
MAX
100
275
100
275
UNITS
ns
tSKEW
Figures 5 and 7, RDIFF = 54Ω, CL1 = CL2
= 100pF
25
90
ns
tR, tF
Figures 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
Figures 5 and 10, RDIFF = 54Ω, CL1 = CL2
= 100pF
100
225
100
225
Driver Output Skew
Driver Rise or Fall Time
Receiver Input to Output
Propagation Delay
tPHL
ns
_______________________________________________________________________________________
3
MAX1480A/B/C/MAX1490A/B
ELECTRICAL CHARACTERISTICS (continued)
MAX1480A/B/C/MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
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
|tPLH - tPHL| Differential Receiver
Skew
Maximum Data Rate
Time to Shutdown
SYMBOL
CONDITIONS
tSKD
Figures 5 and 10, RDIFF = 54Ω, CL1 = CL2
= 100pF
fMAX
tPLH, tPHL < 50% of data period
MIN
TYP
MAX
20
ns
2.5
tSHDN
UNITS
Mbps
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
Driver Input to Output
Propagation Delay
Driver Output Skew
Driver Rise or Fall Time
SYMBOL
tPLH
tPHL
CONDITIONS
Figures 5 and 7, RDIFF = 54Ω,
CL1 = CL2 = 100pF
MIN
TYP
MAX
2
3.0
2
3.0
UNITS
µs
tSKEW
Figures 5 and 7, RDIFF = 54Ω,
CL1 = CL2 = 100pF
900
1600
ns
tR, tF
Figures 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
4
_______________________________________________________________________________________
Complete, Isolated RS-485/RS-422
Data Interface
MAX1480A/B/C, MAX1490A/B
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
Figures 5 and 10, RDIFF = 54Ω,
CL1 = CL2 = 100pF
2
3.0
2
3.0
Receiver Input to Output
Propagation Delay
|tPLH - tPHL| Differential Receiver
Skew
Maximum Data Rate
Time to Shutdown
tPHL
tSKD
Figures 5 and 10, RDIFF = 54Ω,
CL1 = CL2 = 100pF
fMAX
tPLH, tPHL < 50% of data period
tSHDN
1200
µs
ns
0.25
Mbps
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
Note 1: All currents into device pins are positive; all currents out of device pins are negative. All voltages are referenced to logicside 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).
_______________________________________________________________________________________
5
__________________________________________Typical Operating Characteristics
(VCC_ = 5V, FS = VCC_, TA = +25°C, unless otherwise noted.)
50
40
30
-20
-15
-10
20
10
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
3.50
3.00
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
-40
0
20
40
60
80
OUTPUT CURRENT vs.
DRIVER OUTPUT LOW VOLTAGE
OUTPUT CURRENT vs.
DRIVER OUTPUT HIGH VOLTAGE
0.2
120
100
80
60
-80
-70
-60
-50
-40
-30
40
-20
0.1
20
-10
0
0
-20
0
20
40
60
80
0
0
1
2
3 4
5
6
7 8
9 10 11 12
TEMPERATURE (°C)
OUTPUT LOW VOLTAGE (V)
DRIVER OUTPUT CURRENT
vs. DIFFERENTIAL OUTPUT VOLTAGE
DRIVER DIFFERENTIAL OUTPUT VOLTAGE
vs. TEMPERATURE
70
60
50
40
30
20
3.0
2.8
2.7
2.6
2.5
2.4
2.3
2.2
10
2.1
0
2.0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
DIFFERENTIAL OUTPUT VOLTAGE (V)
DI´ = HIGH OR OPEN
RL = 54Ω
2.9
-7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6
OUTPUT HIGH VOLTAGE (V)
MAX1480/90A/B-08
DI´ = HIGH OR OPEN
DIFFERENTIAL OUTPUT VOLTAGE (V)
80
MAX1480/90A/B-06
MAX1480/90A/B-05
140
-90
MAX1480B/MAX1480C/MAX1490B
SHUTDOWN CURRENT vs. TEMPERATURE
0.40
MAX1480/90A/B-09
0.3
160
-100
OUTPUT CURRENT (mA)
0.4
180
OUTPUT CURRENT (mA)
0.5
0
-20
RECEIVER OUTPUT LOW VOLTAGE
vs. TEMPERATURE
MAX1480/90A/B-07
OUTPUT LOW VOLTAGE (V)
3.75
TEMPERATURE (°C)
0.6
-40
6
4.00
OUTPUT HIGH VOLTAGE (V)
MEASURED AT ISO RO DRV
IRO = 8mA
0.7
4.25
OUTPUT LOW VOLTAGE (V)
MAX1480/90A/B-04
0.8
4.50
3.25
0
0
MEASURED AT ISO RO DRV
IRO = 8mA
4.75
-5
MAX1480/90A/B-03
-25
5.00
OUTPUT HIGH VOLTAGE (V)
60
MEASURED AT ISO RO DRV
SD = VCC_, DI´ = VCC_
DE´ (MAX1480B/C ONLY) = VCC_
MEASURED AT VCC1 AND VCC2
0.35
SHUTDOWN CURRENT (μA)
OUTPUT CURRENT (mA)
70
-30
RECEIVER OUTPUT HIGH VOLTAGE
vs. TEMPERATURE
MAX1480/90A/B-02
MEASURED AT ISO RO DRV
OUTPUT CURRENT (mA)
80
OUTPUT CURRENT vs.
RECEIVER OUTPUT HIGH VOLTAGE
MAX1480/90A/B-01
OUTPUT CURRENT vs.
RECEIVER OUTPUT LOW VOLTAGE
OUTPUT CURRENT (mA)
MAX1480A/B/C, MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
0.30
0.25
0.20
0.15
0.10
0.05
0
-40
-20
0
20
40
TEMPERATURE (°C)
60
80
-40
-20
0
20
40
TEMPERATURE (°C)
_______________________________________________________________________________________
60
80
Complete, Isolated RS-485/RS-422
Data Interface
(VCC_ = 5V, FS = VCC_, TA = +25°C, unless otherwise noted.)
VCC = 4.5V
100
DE´ = VCC
RL = ∞
80
60
40
VCC = 5.5V
VCC = 4.5V
20
RL = 54Ω
VCC = 5.5V
VCC = 5.0V
100
120
100
VCC = 4.5V
80
DE´ = VCC
60
VCC = 5.5V
VCC = 5.0V
RL = ∞
VCC = 5.0V
RL = 54Ω
VCC = 5.5V
110
VCC = 5.0V
90
VCC = 4.5V
80
DE´ = VCC
70
60
VCC = 5.5V
50
30
VCC = 4.5V
20
20
40
60
80
-40
TEMPERATURE (°C)
-20
0
20
40
60
-20
0
180
VCC = 5.0V
VCC = 4.5V
140
VCC = 5.5V
VCC = 5.0V
40
60
80
TEMPERATURE (°C)
RL = ∞
150
VCC = 5.5V
140
VCC = 5.0V
130
SUPPLY CURRENT (mA)
RL = 54Ω
VCC = 5.5V
20
MAX1490B
SUPPLY CURRENT vs. TEMPERATURE
MAX1480/90A/B-13
200
120
-40
TEMPERATURE (°C)
MAX1490A
SUPPLY CURRENT vs. TEMPERATURE
160
VCC = 4.5V
20
80
MAX1480/90A/B-14
0
VCC = 4.5V
120
RL = 54Ω
110
100
90
80
VCC = 5.0V
VCC = 5.5V
RL = ∞
70
100
60
VCC = 4.5V
80
-20
0
20
40
60
20
40
60
DRIVER ENABLE TIME
vs. TEMPERATURE
MAX1480/90A/B-15a
MAX1480B
MAX1480C
RL = 54Ω
VDI´ = 0V MEASURED FROM
DE´ TO VALID OUTPUT
0
20
40
TEMPERATURE (°C)
80
100
MAX1480B
10
RL = 54Ω
VDI´ = 0V MEASURED FROM
DE´ TO VALID OUTPUT
1
MAX1480C
MAX1480A
MAX1480A
0.1
-20
0
DRIVER DISABLE TIME
vs. TEMPERATURE
10
-40
-20
TEMPERATURE (°C)
100
1
-40
80
TEMPERATURE (°C)
DRIVER ENABLE TIME (μs)
-40
VCC = 4.5V
50
MAX1480/90A/B-15b
-20
SUPPLY CURRENT (mA)
-40
RL = ∞
VCC = 5.0V
40
40
0
MAX1480/90A/B-12
120
MAX1480C
SUPPLY CURRENT vs. TEMPERATURE
MAX1480/90A/B-11
140
SUPPLY CURRENT (mA)
VCC = 5.0V
120
DRIVER DISABLE TIME (μs)
SUPPLY CURRENT (mA)
RL = 54Ω
VCC = 5.5V
140
MAX1480/90A/B-10
160
MAX1480B
SUPPLY CURRENT vs. TEMPERATURE
SUPPLY CURRENT (mA)
MAX1480A
SUPPLY CURRENT vs. TEMPERATURE
0.1
60
80
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
_______________________________________________________________________________________
7
MAX1480A/B/C, MAX1490A/B
_____________________________Typical Operating Characteristics (continued)
_____________________________Typical Operating Characteristics (continued)
(VCC_ = 5V, FS = VCC_, VDI´ = 0V, DE´ toggled 0V to 5V at 5kHz, TA = +25°C, unless otherwise noted.)
MAX1480/90-19
MAX1480/90-20
MAX1480A
DRIVER DISABLE TIME
MAX1480A
DRIVER ENABLE TIME
DRIVER
OUTPUT B
2V/div
DRIVER
OUTPUT B
2V/div
DE´
2V/div
DE´
2V/div
200ns/div
VCC_ = 5.0V, DI´ = 0V
DE´ TOGGLED 0V TO 5V AT 5kHz
200ns/div
VCC_ = 5.0V, DI´= 0V
DE´ TOGGLED 0V TO 5V AT 5kHz
MAX1480/90-17
MAX1480/90-18
MAX1480B
DRIVER DISABLE TIME
MAX1480B
DRIVER ENABLE TIME
DRIVER
OUTPUT B
2V/div
DRIVER
OUTPUT B
2V/div
DE´
2V/div
DE´
2V/div
5μs/div
VCC_ = 5.0V, DI´= 0V
DE´ TOGGLED 0V TO 5V AT 5kHz
10μs/div
VCC_ = 5.0V, DI´= 0V
DE´ TOGGLED 0V TO 5V AT 5kHz
MAX1480/90-26
MAX1480C
DRIVER DISABLE TIME
MAX1480C
DRIVER ENABLE TIME
MAX1480/90-25
MAX1480A/B/C, MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
500ns/div
VCC_ = 5.0V, DI´= 0V
DE´ TOGGLED 0V TO 5V AT 5kH
8
DRIVER
OUTPUT B
2V/div
DRIVER
OUTPUT B
2V/div
DE´
2V/div
DE´
2V/div
500ns/div
VCC_ = 5.0V, DI´ = 0V
DE´ TOGGLED 0V TO 5V AT 5kHz
_______________________________________________________________________________________
Complete, Isolated RS-485/RS-422
Data Interface
(VCC_ = 5V, FS = VCC_, DE´ = VCC_, VDI´ = 0V to 5V at 1.25MHz, TA = +25°C, unless otherwise noted.)
MAX1480A/MAX1490A
RECEIVER tPHL
MAX1480A/MAX1490A
RECEIVER tPLH
MAX1480/90-21
MAX1480/90-22
RECEIVER
INPUT A
1V/div
RECEIVER
INPUT B
1V/div
RECEIVER
INPUT B
1V/div
RECEIVER
INPUT A
1V/div
RO/RO
2V/div
RO/RO
2V/div
20ns/div
20ns/div
VCC_ = 5.0V, DE´= VCC_
DI´ = 0V TO 5V AT 1.25MHz
VCC_ = 5.0V, DE´= VCC_
DI´ = 0V TO 5V AT 1.25MHz
MAX1480B/MAX1480C/MAX1490B
RECEIVER tPHL
MAX1480B/MAX1480C/MAX1490B
RECEIVER tPLH
MAX1480/90-23
MAX1480/90-24
RECEIVER
INPUT A
1V/div
RECEIVER
INPUT A
1V/div
RECEIVER
INPUT B
1V/div
RECEIVER
INPUT B
1V/div
RO/RO
2V/div
RO/RO
2V/div
200ns/div
500ns/div
VCC_ = 5.0V, DE´= VCC_
DI´= 0V TO 5V AT 125kHz
VCC_ = 5.0V, DE´= VCC_
DI´= 0V TO 5V AT 125kHz
MAX1480/90-16
POWER-UP DELAY TO DRIVER OUTPUTS VALID
DRIVER
OUTPUT B
(Z FOR MAX1490)
2V/div
SD
2V/div
1μs/div
VDI´ = 0V
VSD = 5V TO 0V AT 1kHz
_______________________________________________________________________________________
9
MAX1480A/B/C, MAX1490A/B
_____________________________Typical Operating Characteristics (continued)
MAX1480A/B/C, MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
________________________________________________________________Pin Description
PIN
MAX1480A/B/C
MAX1490A/B
NAME
PINS
PINSON
ONTHE
THENON-ISOLATED
NON-ISOLATEDSIDE
SIDE
1, 2, 8, 10
1, 2, 8, 10
VCC1–VCC4
3, 4
3, 4
D1, D2
5
5
GND1
FUNCTION
Logic-Side (nonisolated side) +5V Supply Voltages
Internal Connections. Leave these pins unconnected.
Logic-Side Ground. Connect to GND2 (pin 12).
6
6
FS
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.
7
7
SD
Shutdown Input. Ground for normal operation. When high, the power oscillator is
disabled.
9
9
DI
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).
11
—
DE
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 outputs 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
RO
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).
12
12
GND2
13
—
RO
14
—
VCC5
Logic-Side Ground. Connect to GND1 (pin 5).
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).
Logic-Side (non-isolated side) +5V Supply Voltage
PINS
PINSON
ONTHE
THEISOLATED
ISOLATEDRS-485/RS-422
RS-485/RS-422SIDE
SIDE
10
15
13
ISO RO LED
16
—
ISO COM2
17
—
ISO DE DRV
18
14
ISO VCC2
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).
Isolated Common. Connect to ISO COM1 (pin 20).
Isolated Driver-Enable Drive. 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 outputs are enabled, the device functions as a line driver. While the driver
outputs are high impedance, the device functions as a line receiver. Opencollector output; must have pullup to ISO VCC_ and be connected to ISO DE IN
for normal operation (Table 1 of Figure 1).
Isolated Supply Voltage. Connect to ISO VCC1 (pin 26 for MAX1480A/B/C, or
pin 22 for MAX1490A/B).
19
15
ISO DI DRV
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).
20
16
ISO COM1
Isolated Common. For MAX1480A/B/C, connect to ISO COM2 (pin 16)
(Figures 1 and 2).
______________________________________________________________________________________
Complete, Isolated RS-485/RS-422
Data Interface
PIN
MAX1480A/B/C
MAX1490A/B
NAME
FUNCTION
PINS ON THE ISOLATED RS-485/RS-422 SIDE (continued)
—
17
Y
Noninverting Driver Output
—
18
Z
Inverting Driver Output
—
19
B
Inverting Receiver Input
—
20
A
Noninverting Receiver Input
21
—
ISO DE IN
Isolated Driver-Enable Input. Connect to ISO DE DRV for normal operation.
22
—
ISO DI IN
Isolated Driver Input. Connect to ISO DI DRV for normal operation.
23
—
A
Noninverting Driver Output and Noninverting Receiver Input
24
21
ISO RO DRV
25
26
27, 28
—
22
23, 24
B
ISO VCC1
AC2, AC1
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).
Inverting Driver Output and Inverting Receiver Input
Isolated Supply Voltage Source
Internal Connections. Leave these pins unconnected.
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).
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 (24pin 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 optocouplers. 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 reducedslew-rate drivers that minimize EMI and reduce reflections 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 protected 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 function as line receivers.
______________________________________________________________________________________
11
MAX1480A/B/C, MAX1490A/B
___________________________________________________Pin Description (continued)
MAX1480A/B/C, MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
VCC3
ISO VCC1
D1
MAX845
Q
FS
OSC
1.07MHz/
1.45MHz
MAX1480A: MAX1487
MAX1480B: MAX487
MAX1480C: MAX487
N
T F/F
ISO DI IN
Q
N
A
ISO DE IN
ISO RO DRV
R
RE
GND1
SD
B
D
D2
ISO COM1
EXTERNAL RS-485/RS-422 WIRING
VIN
5V
C1
C2
22μF
0.1μF
TERMINATING RESISTOR
(ONE RESISTOR ON EACH END)
MAX1480A/B/C
VCC1
1
28 AC1 (MAKE NO CONNECTION)
VCC2
2
27 AC2 (MAKE NO CONNECTION)
26 ISO VCC1
B
25
D1 3
D2 4
GND1
5
FS 6
SD
7
74HC86
OR EQUIVALENT
DI
VCC3
R1
DRIVER INPUT
DI´
DE
R2
DRIVER ENABLE
DE´
R3
RECEIVER OUTPUT
DI
VCC4
DE
GND2
24
MAX845
MAX1487
MAX487
VCC5
A
TWISTED PAIR
TO OTHER TRANSCEIVERS
23 A
9
20 ISO COM1
10
19 ISO DI DRV
11
18 ISO VCC2
12
17 ISO DE DRV
16
15
SH
R6
RL
ISO DE IN
21
LOGIC GROUND
SHIELD (OPTIONAL)
ISO RO DRV
8
14
RL
B
22 ISO DI IN
RO 13
RO
TWISTED PAIR
TO OTHER TRANSCEIVERS
R4
SHIELD (OPTIONAL)
R5
R7
100Ω
ISO COM2
NOTE: RESISTOR R7 PROTECTS
THE MAX1480A/B/C FROM TRANSIENT
CURRENTS BETWEEN SHIELD AND
TRANSMISSION LINES.
ISO RO LED
ISOLATION BARRIER
ISOLATED COMMON
Table 1. Pull-Up and LED Drive Resistors
PART
R1 (Ω)
R2 (Ω)
R3 (Ω)
R4 (Ω)
R5 (Ω)
R6 (Ω)
MAX1480A
200
200
1000
4300
1000
200
MAX1480B
200
510
3000
2200
3000
200
MAX1480C
200
200
3000
3000
3000
200
Figure 1. MAX1480A/MAX1480B/MAX1480C Detailed Block Diagram and Typical Application Circuit
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 CMOSlogic families with only resistive pullup.
12
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.
______________________________________________________________________________________
Complete, Isolated RS-485/RS-422
Data Interface
D1
MAX845
Q
OSC
1.07MHz/
1.45MHz
FS
N
A
R
T F/F
ISO RO DRV
D2
Q
B
ISO DI DRV
N
MAX1490A: MAX490
MAX1490B: MAX488
Z
D
SD
Y
GND1
MAX1490A/B
EXTERNAL RS-485/RS-422 WIRING
VIN
5V
C1
VCC1
C2
VCC2
22μF
0.1μF
D1
1
24 AC1 (MAKE NO CONNECTION)
2
23 AC2 (MAKE NO CONNECTION)
3
22 ISO VCC1
DI
R1
DRIVER INPUT
DI´
RECEIVER OUTPUT
RO
R2
RL
20 A
A
19 B
B
SD 7
18 Z
Z
VCC3 8
17 Y
MAX488
MAX490
MAX845
5
FS 6
74HC86
OR EQUIVALENT
TWISTED PAIR
TO OTHER TRANSCEIVERS
21 ISO RO DRV
D2 4
GND1
TERMINATING RESISTOR
(ONE RESISTOR ON EACH END)
DI 9
16 ISO COM1
VCC4 10
15 ISO DI DRV
13 ISO RO LED
GND2 12
SHIELD (OPTIONAL)
RL
TWISTED PAIR
TO OTHER TRANSCEIVERS
Y
R5, 100Ω
R4
14 ISO VCC2
R0 11
RL
RL
SH1
SH2
SHIELD (OPTIONAL)
R6, 100Ω
R3
ISOLATION BARRIER
ISOLATED COMMON
NOTE: RESISTORS R5 AND R6 PROTECT
THE MAX1490A/B FROM TRANSIENT
CURRENTS BETWEEN SHIELD AND
TRANSMISSION LINES.
LOGIC GROUND
Table 2. Pull-Up and LED Drive Resistors
PART
R1 (Ω)
R2 (Ω)
R3 (Ω)
R4 (Ω)
MAX1490A
200
1000
330
1000
MAX1490B
200
3000
330
3000
Figure 2. MAX1490A/MAX1490B Detailed Block Diagram and Typical Application Circuit
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 Pchannel MOSFET as shown in Figure 3. In normal opera-
tion, SD is low, turning the MOSFET on and thereby providing 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 optocouplers. In normal operating mode, the switch carries only
the optocoupler currents, so an on-resistance of several
ohms will not significantly degrade efficiency.
______________________________________________________________________________________
13
MAX1480A/B/C, MAX1490A/B
VCC3
MAX1480A/B/C, MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
VIN
5V
Si943304
VCC1 1
28 AC1
VCC2 2
27 AC2
D1 3
26 ISO VCC1
D2 4
25 B
24 ISO RO DRV
GND1 5
P
FS 6
SHUTDOWN
R1
DI
R2
MAX845
MAX1487
R3
22 ISO DI IN
VCC3 8
21 ISO DE IN
DI 9
20 ISO COM1
VCC4 10
19 ISO DI DRV
18 ISO VCC2
GND2 12
17 ISO DE DRV
RO 13
RO
23 A
SD 7
DE 11
DE
MAX1480A
VCC5
16 ISO COM2
15 ISO RO LED
14
ISOLATION BARRIER
GND
Figure 3. MAX1480A Low-Power Shutdown Mode
Test Circuits
ISOLATION BARRIER
D
ISOLATION BARRIER
(DE´)
R
R
VOC
DI´
D
RDIFF
VID
CL2
Figure 4. Driver DC Test Load
14
( ) ARE FOR
THE MAX1480A/B/C
CL1
VOD
R
RO (RO)*
* OPTOCOUPLER
OUTPUTS. SEE FIGURES 1
AND 2 FOR DETAILED BLOCK
DIAGRAM AND TYPICAL
APPLICATION CIRCUIT.
Figure 5. Driver/Receiver Timing Test Circuit
______________________________________________________________________________________
Complete, Isolated RS-485/RS-422
Data Interface
ISO VCC_
S1
500Ω
OUTPUT
UNDER TEST
CL
S2
Figure 6. Driver Timing Test Load
Switching Waveforms
VCC_ - 0.4V
DI´
VCC_ - 0.4V
2
VCC_ - 0.4V
2
0V
tPLH
DE´
tPHL
0V
1/2 VO
VCC_ - 0.4V
2
VCC_ - 0.4V
2
tLZ
tZL
B
A, B
VO
A
2.3V OUTPUT NORMALLY LOW
VOL
1/2 VO
VO
VDIFF 0V
-VO
VCC_ -0.4V
10%
VDIFF = V (A) - V (B)
tR
OUTPUT NORMALLY HIGH
A, B
90%
90%
VOH - 0.5V
2.3V
10%
0V
tF
tZH
tSKEW = ⎢tPLH - tPHL ⎢
Figure 7. Driver Propagation Delays and Transition Times
tHZ
Figure 8. Driver Enable and Disable Times
INPUT
VID
2.4V
SD
0.8V
1.6V
tZL(SHDN)
-VID
VA - VB
MAX1490A/B
OUTPUT
tSHDN
A, B
VOL
0V
0V
1.6V
2.3V OUTPUT NORMALLY LOW
VOL + 0.5V
VOL + 0.5V
RO VOH
VOL
1.5V
tPLH
1.5V
tPHL
OUTPUT NORMALLY HIGH
A, B
VOH - 0.5V
2.3V
0V
tZH(SHDN)
Figure 9. Times to/from Shutdown
tSHDN
RO
VOH
VOL
1.5V
tPHL
MAX1480A/B/C
OUTPUT
1.5V
tSKEW = ⏐tPLH - tPHL⏐
tPLH
Figure 10. Receiver Propagation Delays
______________________________________________________________________________________
15
MAX1480A/B/C, MAX1490A/B
____________________________________________________Test Circuits (continued)
MAX1480A/B/C, MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
MAX1480B/MAX1480C/MAX1490B:
Reduced EMI and Reflections
_____________________Function Tables
The MAX1480B/MAX1480C/MAX1490B are slew-ratelimited, 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-frequency harmonics with large amplitudes are evident.
Figure 12 shows the same information for the slew-ratelimited MAX1480B/MAX1480C/MAX1490B transmitting
the same signal. The high-frequency harmonics have
much lower amplitudes, and therefore the potential for
EMI is significantly reduced.
Half-Duplex Devices
(MAX1480A/MAX1480B/MAX1480C)
Table 3. Transmitting
INPUTS*
OUTPUTS
DE´
DI´
B
A
1
1
0
1
1
0
1
0
0
X
High-Z
High-Z
X = Don’t care
High-Z = High impedance
Table 4. Receiving
INPUTS*
10dB/div
0Hz
DE´
VA - VB
OUTPUT
(RO)
0
≥ +0.2V
0
0
≤ -0.2V
1
0
Open
0
5MHz
Full-Duplex Devices
(MAX1490A/MAX1490B)
500kHz/div
Figure 11. Driver Output Waveform and FFT Plot of
MAX1480A/MAX1490A Transmitting a 150kHz Signal
Table 5. Transmitting
INPUT*
OUTPUTS
(DI´)
Z
Y
1
0
1
0
1
0
* 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).
10dB/div
Table 6. Receiving
0Hz
5MHz
500kHz/div
Figure 12. Driver Output Waveform and FFT Plot of
MAX1480B/MAX1480C/MAX1490B Transmitting a 150kHz
Signal
16
INPUT
(VA - VB)
OUTPUT
(RO)
≥ +0.2V
1
≤ -0.2V
0
Open
1
______________________________________________________________________________________
Complete, Isolated RS-485/RS-422
Data Interface
MAX1480A/B/C, MAX1490A/B
TERMINATING RESISTOR
(ONE RESISTOR ON EACH END)
B
DI
D
120Ω
DE
A
A
B
A
B
RO
R
100Ω
RE
R
RE
R
RE
D
RO DE
D
DI
VIN
5V
C1
C2
22μF
0.1μF
DI
RO DE
VCC1
1
28 AC1 (MAKE NO CONNECTION)
VCC2
2
27 AC2 (MAKE NO CONNECTION)
26 ISO VCC1
D1 3
FS 6
SD
DI
DE
VCC3
DRIVER INPUT
DRIVER ENABLE
R1
R2
R3
RECEIVER OUTPUT
RO
DI
VCC4
DE
GND2
24
MAX845
MAX487
MAX1487
ISO RO DRV
23 A
22 ISO DI IN
7
ISO DE IN
8
21
9
20 ISO COM1
10
19 ISO DI DRV
11
18 ISO VCC2
12
17 ISO DE DRV
RO 13
VCC5
14
LOGIC GROUND
B
25 B
D2 4
GND1
5
74HC86
OR EQUIVALENT
TERMINATING RESISTOR
(ONE RESISTOR ON EACH END)
MAX1480A/B/C
16
15
ISOLATION BARRIER
A
R6
120Ω
SH
R4
R5
SHIELD
(OPTIONAL)
NOTE: RESISTOR R7 PROTECTS
THE MAX1480A/B/C FROM
TRANSIENT CURRENTS
BETWEEN SHIELD AND
TRANSMISSION LINES.
R7
100Ω
ISO COM2
ISO RO LED
ISOLATED COMMON
Figure 13. Typical Half-Duplex RS-485/RS-422 Network
______________________________________________________________________________________
17
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 circuits over the entire common-mode range (see the
Typical Operating Characteristics). In addition, a thermal 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 difference between the low-to-high and high-to-low propagation 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.
C1
C2
22μF
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 application 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.
VCC1
1
24 AC1 (MAKE NO CONNECTION)
VCC2
2
23 AC2 (MAKE NO CONNECTION)
0.1μF
D1 3
22 ISO VCC1
D2 4
21 ISO RO DRV
FS 6
MAX488
MAX490
GND1 5
SD 7
74HC86
OR EQUIVALENT
VCC3
R1
DI
DRIVER INPUT
DI´
R2
8
RECEIVER OUTPUT
120Ω
A
19 B
B
18 Z
Z
17 Y
Y
16 ISO COM1
VCC4 10
15 ISO DI DRV
R4
13 ISO RO LED
ISOLATION BARRIER
SH2
ISOLATED COMMON
120Ω
R
RO
B
120Ω
A
SHIELD (OPTIONAL)
NOTE: RESISTORS R5 AND R6 PROTECT
THE MAX1490A/B FROM TRANSIENT
CURRENTS BETWEEN SHIELD AND
TRANSMISSION LINES.
LOGIC GROUND
Figure 14. Typical Full-Duplex RS-485/RS-422 Network
18
DI
SHIELD (OPTIONAL)
R6, 100Ω
R3
D
Z
R5, 100Ω
SH1
14 ISO VCC2
GND2 12
Y
120Ω
20 A
DI 9
RO 11
RO
___________Applications Information
MAX1490A/B
VIN
5V
MAX845
MAX1480A/B/C, MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
______________________________________________________________________________________
Complete, Isolated RS-485/RS-422
Data Interface
• 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 resistor 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 specifications 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 isolated 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 100Ω resistor.
In the case of the MAX1490, each shield should have
its own 100Ω resistor (Figures 1, 2, 13, and 14).
+5V
+5V
NETWORK SEGMENT B
NETWORK SEGMENT A
2 8 10 14
A
23
B
25
2 8 10 14
3kΩ
13
1
26
3kΩ
9
11
24
200Ω
200Ω
4
9
MAX1480C
3
13
DRIVER
ENABLE
B>A
23
A
25
B
26
3kΩ
74HC04
MAX1480C
19
22
17
21
3kΩ
200Ω
2
DRIVER
ENABLE
200Ω
A>B
3kΩ
19
22
17
21
11
3kΩ
24
200Ω
200Ω
15
15
5 7 12
5 7 12
+5V
+5V
51kΩ 1000pF
16
15
2 B
7
14
Q 13
74HC123
Q 4
CLR
3
6
Q 5
10 B
74HC123
1 A
51kΩ 1000pF
9 A
Q 12
CLR
11
Figure 15. Doubly Isolated RS-485 Repeater
______________________________________________________________________________________
19
MAX1480A/B/C, MAX1490A/B
Connections and components from one side should
not be located near those of the other side.
MAX1480A/B/C, MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
Doubly Isolated RS-485 Repeater
The RS-422/RS-485 standard is specified for cable
lengths up to 4000 feet. When approaching or exceeding the specified maximum cable length, a groundpotential 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 currents are by their nature unstable and unpredictable. In
addition, they may cause noise to be injected into sensitive instrumentation and, in severe cases, might actually 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.
20
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 transmissions. All receivers receive all data; if this is undesirable, 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 represents 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 isolation is not needed, one of the MAX1480C devices can
be replaced by a MAX487 for 250kbps applications.
______________________________________________________________________________________
Complete, Isolated RS-485/RS-422
Data Interface
Ordering Information (continued)
PART†
TOP VIEW
MAX1480A/B/C
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
24 Wide Plastic DIP
VCC1 1
28 AC1
VCC2 2
27 AC2
MAX1490ACPG
0°C to +70°C
D1 3
26 ISO VCC1
MAX1490AEPG
-40°C to +85°C
24 Wide Plastic DIP
D2 4
25 B
MAX1490BCPG
0°C to +70°C
24 Wide Plastic DIP
24 ISO RO DRV
MAX1490BEPG
-40°C to +85°C
24 Wide Plastic DIP
23 A
†Data rate for “A” parts is up to 2.5Mbps. Data rate for “B” and
GND1 5
FS 6
MAX845
MAX487
MAX1487
SD 7
22 ISO DI IN
VCC3 8
21 ISO DE IN
DI 9
20 ISO COM1
VCC4 10
19 ISO DI DRV
18 ISO VCC2
DE 11
17 ISO DE DRV
GND2 12
RO 13
16 ISO COM2
VCC5 14
15 ISO RO LED
“C” parts is up to 250kbps.
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.
PACKAGE TYPE
PACKAGE CODE
DOCUMENT NO.
28 PDIP
P28M-1
21-0044
ISOLATION BARRIER
DIP
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.
MAX1480A/B/C, MAX1490A/B
Pin Configurations (continued)