MAXIM MAX1480E, MAX1490E User Manual

_________________General Description

The MAX1480EA/MAX1480EC/MAX1490EA/MAX1490EB
are complete, electrically isolated, RS-485/RS-422 data
communications interface solutions in a hybrid microcir­cuit. The RS-485/RS-422 I/O pins are protected against
±15kV electrostatic discharge (ESD) shocks, without
latchup. 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.

The MAX1480EC/MAX1490EB feature reduced-slew-rate
drivers that minimize EMI and reduce reflections caused
by improperly terminated cables, allowing error-free data
transmission at data rates up to 160kbps. The
MAX1480EA/MAX1490EA driver slew rate is not limited,
allowing transmission rates up to 2.5Mbps. The
MAX1480EA/MAX1480EC are designed for half-duplex
communication, while the MAX1490EA/MAX1490EB 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
MAX1480EA/MAX1480EC, RO high for the MAX1490EA/
MAX1490EB) if the input is open circuit.

The MAX1480EA/MAX1480EC/MAX1490EA/MAX1490EB
withstand 1260V

RMS

(1min) or 1520V

RMS

(1s). Their iso­lated outputs meet all RS-485/RS-422 specifications. The
MAX1480EA/MAX1480EC are available in a 28-pin DIP
package, and the MAX1490EA/MAX1490EB 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
Telecom

____________________________Features

♦ Isolated Data Interface, Guaranteed to 1260V

RMS

(1min)

♦ ±15kV ESD Protection on I/O Pins
♦ Slew-Rate Limited for Errorless Data

Transmission (MAX1480EC/MAX1490EB)

♦ High-Speed, Isolated, 2.5Mbps RS-485/RS-422

Interface (MAX1480EA/MAX1490EA)

♦ Full-Duplex Data Communication

(MAX1490EA/MAX1490EB)

♦ Single +5V Supply
♦ Current Limiting and Thermal Shutdown for

Driver Overload Protection

♦ Standard 0.6in DIP Packages

28-Pin DIP (MAX1480EA/MAX1480EC)
24-Pin DIP (MAX1490EA/MAX1490EB)

MAX1480E/MAX1490E

±15kV ESD-Protected, Isolated RS-485/RS-422

Data Interfaces

________________________________________________________________ Maxim Integrated Products 1

Pin Configurations

1

24

23

22

21

20

19

18

17

2

3

4

5

6

7

8

AC1

AC2

ISO V

CC1

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 V

CC2

ISO RO LED

GND2

RO

DI

DIP

V

CC2

V

CC3

V

CC4

V

CC1

MAX1490EA/

MAX1490EB

MAX845E

MAX488E

MAX490E

TOP VIEW

ISOLATION BARRIER

19-1940; Rev 0; 4/01

PART

†

MAX1480EACPI

MAX1480EAEPI -40°C to +85°C

0°C to +70°C

TEMP. RANGE PIN-PACKAGE

28 Wide Plastic DIP*

28 Wide Plastic DIP*

_______________Ordering Information

Ordering Information continued at end of data sheet.

†

Data rate for A parts is up to 2.5Mbps. Data rate for C parts is

up to 250kbps.
*See Reliability section at end of data sheet.

Pin Configurations continued at end of data sheet.

Selector Guide appears at end of data sheet.

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

mA

MAX1480E/MAX1490E

±15kV ESD-Protected, Isolated RS-485/RS-422
Data Interfaces

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(V

CC_

= +5V ±10%, VFS= V

CC_

, TA= T

MIN

to T

MAX

, unless otherwise noted. Typical values are at V

CC_

= +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 (V

CC_

)..........................................-0.3V to +6V

Control Input Voltage (SD, FS)..............-0.3V to (V

CC_

+ 0.3V)

Receiver Output Voltage (RO, RO).......-0.3V to (V

CC_

+ 0.3V)

Output Switch Voltage (D1, D2).......................................+12V

With Respect to ISO COM_

Control Input Voltage (ISO DE_) ....-0.3V to (ISO V

CC_

+ 0.3V)

Driver Input Voltage (ISO DI_) .......-0.3V to (ISO V

CC_

+ 0.3V)

Receiver Output Voltage (ISO RO_)

..-0.3V to (ISO V

CC_

+ 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 (T

A

= +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

MAX1480E_CPI/MAX1490E_CPI ........................0°C to +70°C

MAX1480E_EPI/MAX1490E_EPI......................-40°C to +85°C

Storage Temperature Range .............................-65°C to +150°C

Lead Temperature (soldering, 10s) .................................+300°C

Operating Supply Current I

CC

1.5 5R = 27Ω (RS-485), Figure 4

R = 50Ω (RS-422)

V

2

V

OD2

Differential Driver Output
(with Load)

VFS= 0

CONDITIONS

535f

SWL

UNITSMIN TYP MAXSYMBOLPARAMETER

FS = V

CC_

or open 725f

SWH

85 120

55 120

MAX1480EA,
DE

´ = V

CC_

or open

145

130

Low

V

0.8V

SDL

MAX1480EC,
DE

´ = V

CC_

or open

Shutdown Input Threshold

SD = V

CC_

High

µA0.2I

SHDN

Shutdown Supply Current
(Note 3)

2.4V

SDH

120

65 125

High
Low

2.4V

FSH

V

0.8V

FSL

FS Input Threshold

DE´, DI´, Figures 1 and 2
DE´, DI´, Figures 1 and 2

VVCC- 0.4V

IH

Input High Voltage

V0.4V

IL

Input Low Voltage

FS low

FS high

µA50FS Input Pullup Current

pA10FS Input Leakage Current

pA10

Shutdown Input Leakage
Current

RL= ∞
RL= 54Ω
RL= ∞
RL= 54Ω

RL= ∞

MAX1490EB

RL= 54Ω

TA= +25°C, f = 1MHz pF10C

ISO

Isolation Capacitance

TA= +25°C, V

ISO

= 50VDC MΩ100 10,000R

ISO

Isolation Resistance

kHzSwitch Frequency

mA

RL= ∞
RL= 54Ω

130 180

MAX1490EA

180

V8V

OD1

Differential Driver Output
(No Load)

TA= +25°C, 1min (Note 4) V

RMS

1260V

ISO

Isolation Voltage

MAX1480E/MAX1490E

±15kV ESD-Protected, Isolated RS-485/RS-422

Data Interfaces

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(V

CC_

= +5V ±10%, VFS= V

CC_

, TA= T

MIN

to T

MAX

, unless otherwise noted. Typical values are at V

CC_

= +5V and TA= +25°C.)

(Notes 1, 2)

SWITCHING CHARACTERISTICS—MAX1480EA/MAX1490EA

(V

CC_

= +5V ±10%, VFS= V

CC_

, TA= T

MIN

to T

MAX

, unless otherwise noted. Typical values are at V

CC_

= +5V and TA= +25°C.)

Driver Disable Time from Low
(MAX1480EA Only)

t

LZ

0.5 1.8 µsFigures 6 and 8, CL= 15pF, S1 closed

Driver Disable Time from High
(MAX1480EA Only)

t

HZ

0.5 1.8 µsFigures 6 and 8, CL= 15pF, S2 closed

Driver Enable to Output Low
(MAX1480EA Only)

t

ZL

1.0 1.8 µsFigures 6 and 8, CL= 100pF, S1 closed

PARAMETER SYMBOL MIN TYP MAX UNITS

Driver Rise or Fall Time t

R, tF

15 50 ns

Receiver Input to Output
Propagation Delay

t

PHL

90 225

ns

Figures 5 and 7, R

DIFF

= 54Ω, CL1= CL2= 100pF

t

PLH

120 225

Driver Enable to Output High
(MAX1480EA Only)

t

ZH

1.0 1.8 µs

Figures 5 and 10, R

DIFF

= 54Ω, CL1= CL2= 100pF

Figures 6 and 8, CL= 100pF, S2 closed

t

PLH

90 275

Figures 5 and 7, R

DIFF

= 54Ω,

CL1= CL2= 100pF

Driver Output Skew

CONDITIONS

t

SKEW

30 100 ns

Driver Input to Output
Propagation Delay

t

PHL

60 275

ns

Figures 5 and 7, R

DIFF

= 54Ω, CL1= CL2= 100pF

-7V ≤ VCM≤ +12V VV

TH

Receiver Differential Threshold

A, B, Y, and Z pins, tested using Human Body
Model, Figures 1 and 2

kVISO I

OSD

ESD Protection

R = 27Ω or 50Ω, Figure 4 V

0.3

∆V

OD

CONDITIONS

Change in Magnitude of
Driver Output Voltage for
Complementary Output States

mA

0.25

R = 27Ω or 50Ω, Figure 4

VCM= 0

kΩR

IN

Receiver Input Resistance

mV∆V

TH

Receiver Input Hysteresis

V4V

OC

Driver Common-Mode Output

1.0

UNITSMIN TYP MAXSYMBOLPARAMETER

V

OUT

= 5.5V µAI

OH

Receiver Output High Current

Using resistor values listed in Tables 1 and 2

-7V ≤ VO≤ 12V (Note 5) mAISO I

OSD

Driver Short-Circuit Current

VV

OL

Receiver Output Low Voltage

Differential

Common mode 0.3

MAX1490EA/
MAX1490EB

MAX1480EA/
MAX1480EC

MAX1480EA/
MAX1480EC

MAX1490EA/
MAX1490EB

0.2

ISO I

IN

Input Current (A, B)

0.8

DE´ = 0,
V

CC_

= 0 or +5.5V

VIN= +12V

VIN= -7V

12

-0.2 0.2

70

0.4

250

100

±15

-7V ≤ VCM≤ +12V

48

(MAX1490E_)

(MAX1480E_)

MAX1480E/MAX1490E

±15kV ESD-Protected, Isolated RS-485/RS-422
Data Interfaces

4 _______________________________________________________________________________________

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 MAX1480EA/

MAX1480EC, Figure 2 for MAX1490EA/MAX1490EB).

Note 3: Shutdown supply current is the current at V

CC1

and V

CC2

when shutdown is enabled.

Note 4: Limit guaranteed by applying 1520V

RMS

for 1s. Test voltage is applied between all pins on one side of the package to all

pins on the other side of the package, e.g., between pins 1–14 and pins 15–28 on the 28-pin package.

Note 5: Applies to peak current (see Typical Operating Characteristics). Although the MAX1480EA/MAX1480EC and

MAX1490EA/MAX1490EB 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—MAX1480EA/MAX1490EA (continued)

(V

CC_

= +5V ±10%, VFS= V

CC_

, TA= T

MIN

to T

MAX

, unless otherwise noted. Typical values are at V

CC_

= +5V and TA= +25°C.)

t

ZH(SHDN)

315Figures 6 and 9, CL= 100pF, S2 closedShutdown to Driver Output High

t

ZH(SHDN)

315

µs

Figures 6 and 9, CL= 100pF, S1 closed

PARAMETER SYMBOL MIN TYP MAX UNITSCONDITIONS

Shutdown to Driver Output Low µs

t

PLH

1.4 3.0Figures 5 and 7, R

DIFF

= 54Ω, CL1= CL2= 100pF

Driver Input to Output
Propagation Delay

t

PHL

1.1 3.0

µs

Figures 5 and 7, R

DIFF

= 54Ω, CL1= CL2= 100pF

Driver Disable Time from High
(MAX1480EC Only)

t

HZ

1.7 4.5 µsFigures 6 and 8, CL= 15pF, S2 closed

Driver Disable Time from Low
(MAX1480EC Only)

t

LZ

2.0 4.5 µsFigures 6 and 8, CL= 15pF, S1 closed

Driver Enable to Output Low
(MAX1480EC Only)

t

ZL

1.4 4.5 µsFigures 6 and 8, CL= 100pF, S1 closed

Driver Enable to Output High
(MAX1480EC Only)

t

ZH

1.4 4.5 µsFigures 6 and 8, CL= 100pF, S2 closed

Time to Shutdown t

SHDN

100 µs

PARAMETER SYMBOL MIN TYP MAX UNITS

Driver Rise or Fall Time t

R, tF

1.0 2.0 µs

|t

PLH

- t

PHL

| Differential

Receiver Skew

t

SKD

200 ns

Receiver Input to Output
Propagation Delay

t

PHL

1.1 3.0

µs

Figures 5 and 10, R

DIFF

= 54Ω, CL1= CL2= 100pF

Maximum Data Rate

Figures 5 and 7, R

DIFF

= 54Ω, CL1= CL2= 100pF

f

MAX

160 kbps

Shutdown to Driver Output Low

t

SKEW

, t

SKD

≤ 25% of data period

t

ZL(SHDN)

t

PLH

0.9 3.0

315

Figures 5 and 10, R

DIFF

= 54Ω, CL1= CL2= 100pF

µsFigures 6 and 9, CL= 100pF, S1 closed

Shutdown to Driver Output High t

ZH(SHDN)

315µsFigures 6 and 9, CL= 100pF, S2 closed

Driver Output Skew

CONDITIONS

t

SKEW

300 1200 nsFigures 5 and 7, R

DIFF

= 54Ω, CL1= CL2= 100pF

t

SKD

30 150Figures 5 and 10, R

DIFF

= 54Ω, CL1= CL2= 100pF

|t

PLH

- t

PHL

| Differential

Receiver Skew

ns

SWITCHING CHARACTERISTICS—MAX1480EC/MAX1490EB

(V

CC_

= +5V ±10%, VFS= V

CC_

, TA= T

MIN

to T

MAX

, unless otherwise noted. Typical values are at V

CC_

= +5V and TA= +25°C.)

t

SHDN

100Time to Shutdown µs

f

MAX

2.5t

SKEW

, t

SKD

, t

PHL

≤ 25% of data periodMaximum Data Rate Mbps

MAX1480E/MAX1490E

±15kV ESD-Protected, Isolated RS-485/RS-422

Data Interfaces

_______________________________________________________________________________________ 5

__________________________________________Typical Operating Characteristics

(V

CC_

= +5V, VFS= V

CC_

, Figures 1 and 2, TA = +25°C, unless otherwise noted.)

OUTPUT CURRENT vs.

RECEIVER OUTPUT LOW VOLTAGE

80

MEASURED AT ISO RO DRV

70

60

50

40

30

OUTPUT CURRENT (mA)

20

10

0

1.00.50 3.53.02.52.0 5.04.54.0
OUTPUT LOW VOLTAGE (V)

RECEIVER OUTPUT LOW VOLTAGE

vs. TEMPERATURE

0.8
MEASURED AT ISO RO DRV

I

= 8mA

RO

0.7

0.6

0.5

0.4

0.3

OUTPUT LOW VOLTAGE (V)

0.2

0.1

0

-40 20

DRIVER OUTPUT CURRENT

vs. DIFFERENTIAL OUTPUT VOLTAGE

80

70

60

50

40

30

OUTPUT CURRENT (mA)

20

10

0

1.00.50 3.53.02.52.0 5.04.54.0

DIFFERENTIAL OUTPUT VOLTAGE (V)

OUTPUT CURRENT vs.

RECEIVER OUTPUT HIGH VOLTAGE

-30
MEASURED AT ISO RO DRV

-25

MAX1480E/90E TOC01

-20

-15

-10

OUTPUT CURRENT (mA)

-5

1.5

0

1.00.50 3.53.02.52.0 5.04.54.0

1.5

OUTPUT HIGH VOLTAGE (V)

OUTPUT CURRENT vs.

DRIVER OUTPUT LOW VOLTAGE

180

160

140

MAX1480E/90E TOC04

120

100

80

60

OUTPUT CURRENT (mA)

40

20

0

123456789101112

0-20 6040 80
TEMPERATURE (°C)

0

OUTPUT LOW VOLTAGE (V)

DRIVER DIFFERENTIAL OUTPUT VOLTAGE

vs. TEMPERATURE

3.0

DI´ = HIGH OR OPEN

MAX1480E/90E TOC07

1.5

DI´ = HIGH OR OPEN

2.9

= 54Ω

R

L

2.8

2.7

2.6

2.5

2.4

2.3

2.2

DIFFERENTIAL OUTPUT VOLTAGE (V)

2.1

2.0

-40 20

0-20 6040 80
TEMPERATURE (°C)

5.00
MEASURED AT ISO RO DRV

I

4.75

4.50

MAX1480E/90E TOC02

4.25

4.00

3.75

OUTPUT HIGH VOLTAGE (V)

3.50

3.25

3.00

-40 20

-100

-90

-80

MAX1480E/90E TOC05

-70

-60

-50

-40

-30

OUTPUT CURRENT (mA)

-20

-10

0

-7

0.40

0.35

0.30

MAX1480E/90E TOC08

0.25

0.20

0.15

SHUTDOWN CURRENT (µA)

0.10

0.05

0

-40 20

RECEIVER OUTPUT HIGH VOLTAGE

vs. TEMPERATURE

= 8mA

RO

0-20 6040 80
TEMPERATURE (°C)

OUTPUT CURRENT vs.

DRIVER OUTPUT HIGH VOLTAGE

-6 -5 -4 -3 -2 -1 1 2 3 4 5 6
OUTPUT HIGH VOLTAGE (V)

0

SHUTDOWN CURRENT

vs. TEMPERATURE

SD = V

, DI´ = V

CC_

DE´= V
MEASURED AT V

CC_

(MAX1480EC ONLY)

CC_

AND V

CC1

CC2

0-20 6040 80
TEMPERATURE (°C)

MAX1480E/90E TOC03

MAX1480E/90E TOC06

MAX1480E/90E TOC09

MAX1480E/MAX1490E

±15kV ESD-Protected, Isolated RS-485/RS-422
Data Interfaces

6 _______________________________________________________________________________________

____________________________Typical Operating Characteristics (continued)

(V

CC_

= +5V, VFS= V

CC_

, Figures 1 and 2, TA = +25°C, unless otherwise noted.)

V

CC_

= 5.0V, DE´= V

CC_

MAX1480EA/MAX1490EA

RECEIVER t

PHL

RO
2V/div

20ns/div

RECEIVER
INPUT A
1V/div

RECEIVER
INPUT B
1V/div

MAX1480E/90E toc14

V

CC_

= 5.0V, DE´= V

CC_

MAX1480EA/MAX1490EA

RECEIVER t

PLH

RO
2V/div

20ns/div

RECEIVER
INPUT B
1V/div

RECEIVER
INPUT A
1V/div

MAX1480E/90E toc15

SUPPLY CURRENT vs. TEMPERATURE

160

DE´ = V

V

CC

V

V

CC

= +5.5V

140

120

100

80

60

SUPPLY CURRENT (mA)

40

20

0

-40 -20 0 20 40 60 80

MAX1480EA

SUPPLY CURRENT vs. TEMPERATURE

= +5.5V

CC

= +5V

V

CC

= +4.5V

CC

V

= +4.5V

V

CC

TEMPERATURE (°C)

= 54Ω

R

L

= ∞

R

L

= +5V

CC

120

110

100

MAX1480E/90E TOC10

90

80

70

60

50

SUPPLY CURRENT (mA)

40

30

20

-40 -20 0 20 40 60 80

DE´ = V

V

CC

V

CC

V

CC

CC

= +5V

V

CC

TEMPERATURE (°C)

MAX1480EC

= +5.5V

= +5V

= +4.5V

= +5.5V

V

CC

SUPPLY CURRENT vs. TEMPERATURE

MAX1490EA

= 54Ω

R

L

= ∞

R

L

= +4.5V

V

CC

200

180

MAX1480E/90E T0C11

160

140

120

SUPPLY CURRENT (mA)

100

= +5.5V

V

CC

= +5V

V

CC

= +4.5V

V

CC

= +5.5V

V

CC

= +5V

V

CC

= +4.5V

V

80

-40 -20 0 20 40 60 80

TEMPERATURE (°C)

CC

R

L

R

L

= 54Ω

= ∞

MAX1480E/90E TOC12

SUPPLY CURRENT vs. TEMPERATURE

150

140

130

120

110

100

90

80

SUPPLY CURRENT (mA)

70

60

50

-40 -20 0 20 40 60 80

MAX1490EB

V

V

= +5V

V

CC

TEMPERATURE (°C)

V

CC

CC

CC

= +5.5V

= +5V

= +4.5V

V

CC

= +5.5V

MAX1480E/90E TOC13

= 54Ω

R

L

= ∞

R

L

= +4.5V

V

CC

MAX1480E/MAX1490E

±15kV ESD-Protected, Isolated RS-485/RS-422

Data Interfaces

_______________________________________________________________________________________ 7

_____________________________Typical Operating Characteristics (continued)

(V

CC_

= +5V, VFS= V

CC_

, V

DI

´

= 0, DE

´ toggled 0 to 5V at 5kHz, Figures 1 and 2, T

A

= +25°C, unless otherwise noted.)

V

= 5.0V, DI´ = 0V

MAX1480EC

DRIVER DISABLE TIME

DE´
2V/div

500ns/div

DRIVER
OUTPUT B
2V/div

MAX1480E/90E TOC19

MAX1480EC/MAX1490EB

200ns/div

PHL

RECEIVER t

´

MAX1480EC

DRIVER ENABLE TIME

MAX1480E/90E toc16

RECEIVER
INPUT A
1V/div

RECEIVER
INPUT B
1V/div

RO
2V/div

MAX1480E/90E TOC18

DRIVER
OUTPUT B
2V/div

MAX1480EC/MAX1490EB

RECEIVER t

PLH

500ns/div

´

MAX1480E/90E toc17

RECEIVER
INPUT A
1V/div

RECEIVER
INPUT B
1V/div

RO
2V/div

V

= 5.0V, DI´= 0V

DE´
2V/div

500ns/div

MAX1480EA/MAX1490EA

POWER-UP DELAY TO DRIVER OUTPUTS VALID

DRIVER

MAX1480E/90E TOC20

OUTPUT B
(Z FOR MAX1490)
2V/div

SD
2V/div

V

= 0

DI´

= 5V TO 0 AT 1kHz

V

SD

1µs/div

MAX1480E/MAX1490E

±15kV ESD-Protected, Isolated RS-485/RS-422
Data Interfaces

8 _______________________________________________________________________________________

________________________________________________________________Pin Description

MAX1490EA/

MAX1490EB

MAX1480EA/

MAX1480EC

ISO RO LED

ISO COM2

ISO COM120 16

Isolated Common. For MAX1480EA/MAX1480EC, connect to ISO COM2 (pin

16) (Figures 1 and 2).

15 13

Isolated Receiver Output LED. Internal LED anode in MAX1480EA/MAX1480EC and
LED cathode in MAX1490EA/MAX1490EB. Connect to ISO RO DRV through a resis­tor (Table 1 for MAX1480EA/MAX1480EC; Table 2 for MAX1490EA/MAX1490EB).

16 — Isolated Common. Connect to ISO COM1 (pin 20).

ISO DE DRV

ISO V

CC2

ISO DI DRV

17 —

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. Open-collector out­put; must have pullup to ISO VCC_ and be connected to ISO DE IN for normal
operation (Table 1).

18 14

Isolated Supply Voltage. Connect to ISO V

CC1

(pin 26 for MAX1480EA/

MAX1480EC, or pin 22 for MAX1490EA/MAX1490EB).

19 15

Isolated Driver-Input Drive. With DE´ high (MAX1480EA/MAX1480EC 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 MAX1480EA/MAX1480EC only)
for normal operation. Open-collector output; connect a pullup resistor to ISO V

CC_

(Table 1 for MAX1480EA/MAX1480EC, Table 2 for MAX1490EA/MAX1490EB).

DI

DE

RO

9 9

Driver Input. With DE´ high (MAX1480EA/MAX1480EC 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 (see Table 1 for
MAX1480EA/MAX1480EC, Table 2 for MAX1490EA/MAX1490EB).

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 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).

— 11

Receiver Output. If A > B by 200mV, RO is high; if A < B by 200mV, RO is low.
Open collector; must have pullup to VCC(Table 2).

GND2

V

CC5

12 12 Logic-Side Ground. Connect to GND1 (pin 5).

14 — Logic-Side (Nonisolated Side) +5V Supply Voltage

GND1

FS

SD

5 5 Logic-Side Ground. Connect to GND2 (pin 12).

6 6

Frequency Select Input. If FS = V

CC_

or is open, switch frequency is high; if FS
= GND, switch frequency is low. For optimal performance and minimal supply
current, connect FS to V

CC_

or leave unconnected.

7 7

Shutdown Input. Ground for normal operation. When high, the power oscillator is
disabled.

NAME

V

CC1–VCC4

D1, D2

PIN

FUNCTION

1, 2, 8, 10 1, 2, 8, 10 Logic-Side (Nonisolated Side) +5V Supply Voltages

3, 4 3, 4 Internal Connections. Leave these pins unconnected.

RO

13 —

Receiver Output. If A > B by 200mV, RO is low; if A < B by 200mV, RO is high.
Open collector; must have pullup to V

CC

(Table 1).

MAX1480E/MAX1490E

±15kV ESD-Protected, Isolated RS-485/RS-422

Data Interfaces

_______________________________________________________________________________________ 9

Detailed Description

The MAX1480EA/MAX1480EC/MAX1490EA/MAX1490EB
are complete, electrically isolated, RS-485/RS-422 data­communications interface solutions. Transceivers, opto­couplers, a power driver, and a transformer in one
standard 28-pin DIP package (24-pin package for the
MAX1490EA/MAX1490EB) 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 high­speed optocouplers. A single +5V supply on the logic
side powers both sides of the interface. The
MAX1480EA/MAX1480EC offer half-duplex communica­tions while the MAX1490EA/MAX1490EB feature full­duplex communication. The functional input/output
relationships are shown in Tables 3 through 6.

The MAX1480EC/MAX1490EB feature reduced-slew-rate
drivers that minimize EMI and reduce reflections caused
by improperly terminated cables, allowing error-free
transmission at data rates up to 160kbps. The
MAX1480EA/MAX1490EA driver slew rate is not limited,
allowing transmission rates up to 2.5Mbps.

The MAX1480EC/MAX1490EB shutdown feature reduces
supply current to as low as 0.2µA by using the SD pin (see
Low-Power Shutdown Mode section).

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 MAX1480EA/MAX1480EC, the driver outputs are
enabled by bringing DE´ high. Driver-enable time is typi­cally 1.0µs. Allow time for the devices to be
enabled before sending data (see Typical Operating
Characteristics). When enabled, driver outputs function
as line drivers. Driver outputs are high impedance when
DE´ is low. When outputs are high impedance, they func­tion as line receivers.

The MAX1480EA/MAX1480EC/MAX1490EA/MAX1490EB
withstand 1260V

RMS

(1min) or 1520V

RMS

(1s). 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 a 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 nonsolated side are low. Therefore, leave
DI´ and DE´ high or floating when in shutdown mode.
Under these conditions, the MAX1480EC/MAX1490EB
supply current is reduced to as low as 0.2µA.

___________________________________________________Pin Description (continued)

Note: For DE´ and DI´ pin descriptions, see Detailed Block Diagram and Typical Application Circuit (Figure 1 for MAX1480EA/

MAX1480EC, Figure 2 for MAX1490EA/MAX1490EB).

Internal Connections. Leave these pins unconnected.

AC2, AC123, 2427, 28

26 22 ISO V

CC1

Isolated Supply Voltage Source

Inverting Driver Output and Inverting Receiver InputB—25

Isolated Receiver-Output Drive. Connect to ISO RO LED through a resistor (see
Table 1 for MAX1480EA/MAX1480EC, Table 2 for MAX1490EA/MAX1490EB).

ISO RO DRV2124

23 — A Noninverting Driver Output and Noninverting Receiver Input

Isolated Driver Input. Connect to ISO DI DRV for normal operation.ISO DI IN—22

Isolated Driver-Enable Input. Connect to ISO DE DRV for normal operation.ISO DE IN—21

Noninverting Receiver InputA20—

Inverting Receiver InputB19—

Inverting Driver OutputZ18—

Noninverting Driver OutputY17—

FUNCTIONNAME

MAX1490EA/

MAX1490EB

MAX1480EA/

MAX1480EC

PIN

MAX1480E/MAX1490E

±15kV ESD-Protected, Isolated RS-485/RS-422
Data Interfaces

10 ______________________________________________________________________________________

The high-speed optocouplers on the MAX1480EA/
MAX1480EC/MAX1490EA consume an additional 10mA
through V

CC5(VCC4

for the MAX1490EA). Therefore, to
completely shut down these devices, use an external P­channel MOSFET as shown in Figure 3. In normal opera­tion, SD is low, turning the MOSFET on and thereby
providing power to all the VCCpins. When SD is pulled
high, the power oscillator is disabled and the switch is
turned off, disconnecting power from the DI and DE opto-

couplers. In normal operating mode, the switch carries
only the optocoupler currents, so an on-resistance of sev­eral ohms does not significantly degrade efficiency.

Figure 1. MAX1480EA/MAX1480EC Detailed Block Diagram and Application Circuit

Table 1. Pullup and LED Drive Resistors for Figure 1

PART R1 (Ω) R2 (Ω) R3 (Ω)

MAX1480EA

MAX1480EC

200

200

200

200

1000

3000

R4 (Ω)

4300

3000

R5 (Ω)

1000

3000

R6 (Ω)

200

200

V

CC3

V

V

GND1

V

V

GND2

V

D1

N

D2

N

GND1

CC1

1

CC2

2

3

D1

D2

4

5

FS

MAX845E

6

SD

7

CC3

8

DI

9

CC4

10

DE

11

12

RO

13

CC5

14

ISOLATION BARRIER ISOLATED COMMON

SD

C2

0.1µF

DI´

DE

MAX845E

R1*

R2*

´

R3*

Q

OSC

V

IN

+5V

DRIVER INPUT

DRIVER ENABLE

RECEIVER OUTPUT

C1

22µF

T F/F

Q

LOGIC GROUND

FS

1.07MHz/

1.45MHz

OR EQUIVALENT

DI

DE

RO

*SEE TABLE 1.

74HC86

MAX1480EA
MAX1480EC

270pF

4kV

MAX1487E
MAX487E

ISO DI IN

ISO DE IN

ISO RO DRV

AC1 (MAKE NO CONNECTION)

28

AC2 (MAKE NO CONNECTION)

27

ISO V

CC1

26

B

25

ISO RO DRV

24

A

23

ISO DI IN

22

ISO DE IN

21

ISO COM1

20

ISO DI DRV

19

ISO V

CC2

18

ISO DE DRV

17

ISO COM2

16

ISO RO LED

15

ISO V

D

RE

ISO COM1

R6*

CC1

R

R4*

R5*

MAX1480EA: MAX1487E

MAX1480EC: MAX487E

EXTERNAL RS-485/RS-422 WIRING

B

A

SH

R7

100Ω

B

A

TERMINATING RESISTOR

(ONE RESISTOR ON EACH END)

TWISTED PAIR

TO OTHER TRANSCEIVERS

SHIELD (OPTIONAL)

TWISTED PAIR

TO OTHER TRANSCEIVERS

SHIELD (OPTIONAL)

NOTE: RESISTOR R7 PROTECTS
THE MAX1480EA FROM TRANSIENT
CURRENTS BETWEEN SHIELD AND
TRANSMISSION LINES.

R

L

R

L

MAX1480E/MAX1490E

±15kV ESD-Protected, Isolated RS-485/RS-422

Data Interfaces

______________________________________________________________________________________ 11

MAX1480EC/MAX1490EB:

Reduced EMI and Reflections

The MAX1480EC/MAX1490EB are slew-rate-limited,
minimizing EMI and reducing reflections caused by
improperly terminated cables. Figure 11 shows both
the driver output waveform of a MAX1480EA/
MAX1490EA 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-rate-limited

MAX1480EC/MAX1490EB transmitting the same signal.
The high-frequency harmonics have much lower ampli­tudes, and therefore the potential for EMI is significantly
reduced.

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-

Figure 2. MAX1490EA/MAX1490EB Detailed Block Diagram and Typical Application Circuit

Table 2. Pullup and LED Drive Resistors for Figure 2

MAX1490EB 200 3000 330 3000

10003301000200MAX1490EA

R4 (Ω)R3 (Ω)R2 (Ω)R1 (Ω)PART

FS

OR EQUIVALENT

DI

RO

*SEE TABLE 2.

V

IN

+5V

74HC86

V

CC3

OSC

1.07MHz/

1.45MHz

C1
22µF

DRIVER INPUT

RECEIVER OUTPUT

Q

T F/F

Q

SD GND1

C2

0.1µF

R1*

´

DI

R2*

LOGIC GROUND

V

CC1

V

CC2

GND1

V

V

GND2

D1

D2

FS

SD

CC3

CC4

R0

DI

MAX845

1

2

3

4

5

6

7

8

9

10

11

12

N

N

MAX1490EA/

MAX1490EB

MAX845

ISOLATION BARRIER

270 pF

4kV

D1

D2

ISO RO DRV

ISO DI DRV

AC1 (MAKE NO CONNECTION)

24

AC2 (MAKE NO CONNECTION)

23

ISO V

CC1

22

ISO RO DRV

21

A

20

B

19

MAX488E

MAX490E

Z

18

Y

17

ISO COM1

16

ISO DI DRV

15

ISO V

CC2

14

ISO RO LED

13

MAX1490EA: MAX490E
MAX1490EB: MAX488E

R3*

R

D

R5, 100Ω

R4*

R6, 100Ω

ISOLATED COMMON

A

B

Z

Y

EXTERNAL RS-485/RS-422 WIRING

TERMINATING RESISTOR

(ONE RESISTOR ON EACH END)

TWISTED PAIR

TO OTHER TRANSCEIVERS

R

A

B

Z

Y

SH1

SH2

L

SHIELD (OPTIONAL)

R

L

NOTE: RESISTORS R5 AND R6 PROTECT
THE MAX1490EA/MAX1490EB FROM
TRANSIENT CURRENTS BETWEEN SHIELD AND
TRANSMISSION LINES.

TWISTED PAIR

TO OTHER TRANSCEIVERS

SHIELD (OPTIONAL)

R

L

R

L

MAX1480E/MAX1490E

±15kV ESD-Protected, Isolated RS-485/RS-422
Data Interfaces

12 ______________________________________________________________________________________

Figure 4. Driver DC Test Load

Figure 5. Driver/Receiver Timing Test Circuit

Test Circuits

Figure 3. MAX1480EA Low-Power Shutdown Mode

MAX1480EA

V

IN

+5V

Si9433DY

SHUTDOWN

R1

DI

´

R2

´

DE

RO

CC1

1

V

CC2

2

D1

3

D2

4

GND1

V

CC3

V

CC4

GND2

V

CC5

5

FS

6

SD

7

8

DI

9

10

DE

11

12

RO

13

14

MAX1487EMAX845

P

R3

28

27

26

25

24

23

22

21

20

19

18

17

16

15

AC1V

AC2

ISO V

CC1

B

ISO RO DRV

A

ISO DI IN

ISO DE IN

ISO COM1

ISO DI DRV

ISO V

CC2

ISO DE DRV

ISO COM2

ISO RO LED

ISOLATION BARRIER

R

D

V

OD

R

V

OC

GND

ISOLATION BARRIER

ISOLATION BARRIER

(DE´)

R

DI´

V

ID

C

L1

DIFF

C

L2

ISOLATION BARRIER

( ) ARE FOR
THE MAX1480EA/MAX1480EC.

RD

* OPTOCOUPLER
OUTPUTS. SEE FIGURES 1
AND 2 FOR DETAILED BLOCK
DIAGRAM AND TYPICAL
APPLICATION CIRCUIT.

RO (RO)*

MAX1480E/MAX1490E

±15kV ESD-Protected, Isolated RS-485/RS-422

Data Interfaces

______________________________________________________________________________________ 13

Figure 6. Driver Timing Test Load

Figure 7. Driver Propagation Delays and Transition Times

Figure 8. Driver Enable and Disable Times

Figure 9. Times to/from Shutdown

Figure 10. Receiver Propagation Delays

Switching Waveforms

____________________________________________________Test Circuits (continued)

_

ISO V

CC

OUTPUT

500Ω

S1

UNDER TEST

C

L

S2

V

V

- 0.4V

CC_

DI´ 0

V

DIFF

- 0.4V

CC_

2

t

PLH

t

PHL

B

V

O

A

1/2 V

O

V

O

0

-V

10%

O

t

R

V

90%

= V (A) - V (B)

DIFF

t

SKEW = tPLH

- t

PHL

V

- 0.4V

t

90%

F

CC_

2

1/2 V

O

10%

V

DE´

CC_

-0.4V

A, B

V

OL

A, B

V

- 0.4V

CC_

2

0

t

ZL

2.3V

OUTPUT NORMALLY LOW

V

- 0.4V

CC_

2

t

LZ

V

+ 0.5V

OL

OUTPUT NORMALLY HIGH

V

0

2.3V

t

ZH

t

HZ

OH

- 0.5V



2.4V

SD

1.6V 1.6V

0.8V

A, B

V

A, B

t

ZL(SHDN)

2.3V

OL

OUTPUT NORMALLY LOW

OUTPUT NORMALLY HIGH

0

2.3V

t

ZH(SHDN)

t

SHDN

t

SHDN

V

V

OL

OH

+ 0.5V

- 0.5V

INPUT

MAX1490EA/MAX1490EB

OUTPUT

1.5V 1.5V
t

PLH

MAX1480EA/MAX1480EC

1.5V

t

PHL

OUTPUT

t

SKEW

VA - V

RO V

RO

V

ID

-V

B

V

V

V

0

ID

OH

OL

OH

OL

= t

1.5V

PLH - tPHL

0

t

PHL

t

PLH



MAX1480E/MAX1490E

±15kV ESD-Protected, Isolated RS-485/RS-422
Data Interfaces

14 ______________________________________________________________________________________

cuits over the entire common-mode range (see Typical
Operating Characteristics). In addition, a thermal shut-

down circuit forces the driver outputs into a high-im
pedance state if the die temperature rises excessively.

Propagation Delay Skew

Propagation delay skew is 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.

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
MAX1480EA/MAX1490EA Transmitting a 150kHz Signal

Figure 12. Driver Output Waveform and FFT Plot of
MAX1480EC/ MAX1490EB Transmitting a 150kHz Signal

_____________________Function Tables

Half-Duplex Devices

(MAX1480EA/MAX1480EC)

Full-Duplex Devices

(MAX1490EA/MAX1490EB)

DI´

AB

DE´

0 011

≥ +0.2V

Open

INPUTS*

0

0

VA- V

B

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

(V

A

- 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 MAX1480EA/
MAX1480EC, Figure 2 for MAX1490EA/MAX1490EB).

OUTPUTS

INPUT*

(DI´

)

10dB/div

0 5MHz

500kHz/div

10dB/div

0 5MHz

500kHz/div

MAX1480E/MAX1490E

±15kV ESD-Protected, Isolated RS-485/RS-422

Data Interfaces

______________________________________________________________________________________ 15

___________Applications Information

These E versions of the MAX1480EA/MAX1480EC/
1490EA/MAX1490EB provide extra protection against
ESD. The rugged MAX1480EA/MAX1480EC/MAX1490EA/
MAX1490EB are intended for harsh environments where
high-speed communication is important. These devices
eliminate the need for transient suppressor diodes or the
use of discrete protection components. The standard
(non-E) MAX1480A/MAX1480C/MAX1490A/MAX1490B
are recommended for applications where cost is critical.

±15kV ESD Protection

As with all Maxim devices, ESD-protection structures are
incorporated on all pins to protect against electrostatic
discharges encountered during handling and assembly.
The driver outputs and receiver inputs have extra protec­tion against static electricity. Maxim’s engineers devel­oped state-of-the-art structures to protect these pins
against ESD of ±15kV without damage. The ESD struc­tures withstand high ESD in all states: normal operation,
shutdown, and powered down. After an ESD event,
Maxim’s MAX1480EA/MAX1480EC/MAX1490EA/
MAX1490EB keep working without latchup. An isolation
capacitor of 270pF 4kV should be placed between ISO
COM and logic ground for optional performance against
an ESD pulse with respect to logic ground.

ESD protection can be tested in various ways; the trans­mitter outputs and receiver inputs of this product family
are characterized for protection to ±15kV using the
Human Body Model.

ESD Test Conditions

The ±15kV ESD test specifications apply only to the A, B,
Y, and Z I/O pins. The test surge may be referenced to
either the ISO COM or to the nonisolated GND (Figures 1
and 2).

Human Body Model

Figure 13 shows the Human Body Model, and Figure 14
shows the current waveform it generates when dis­charged into low impedance. This model consists of a
100pF capacitor charged to the ESD voltage of interest,
which is then discharged into the test device through a

1.5kΩ resistor.

Machine Model

The Machine Model for ESD tests all pins using a 200pF
storage capacitor and zero discharge resistance. Its
objective is to simulate the stress caused by contact that
occurs with handling and assembly during manufactur­ing. All pins require this protection during manufactur­ing—not just inputs and outputs. Therefore, after PC
board assembly, the Machine Model is less relevant to
I/O ports.

The MAX1480EA/MAX1480EC are designed for bidirec­tional data communications on multipoint bus-transmis­sion lines. The MAX1490EA/MAX1490EB are designed
for full-duplex bidirectional communications that are pri­marily point-to-point. Figures 15 and 16 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 MAX1480EC/MAX1490EB are more tol­erant of imperfect termination and stubs off the main line.

Layout Considerations

The MAX1480EA/MAX1480EC/MAX1490EA/MAX1490EB
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 MAX1480EA/

Figure 13. Human Body ESD Test Model

Figure 14. Human Body Current Waveform

R

1MΩ

C RD

CHARGE-CURRENT

LIMIT RESISTOR

HIGH-

VOLTAGE

DC

SOURCE

C

s

100pF

1500Ω

DISCHARGE

RESISTANCE

STORAGE
CAPACITOR

DEVICE

UNDER

TEST

IP 100%

90%

AMPERES

36.8%

10%

0

0

t

RL

I

r

TIME

t

DL

CURRENT WAVEFORM

PEAK-TO-PEAK RINGING
(NOT DRAWN TO SCALE)

MAX1480E/MAX1490E

±15kV ESD-Protected, Isolated RS-485/RS-422
Data Interfaces

16 ______________________________________________________________________________________

Figure 15. Typical Half-Duplex RS-485/RS-422 Network

TERMINATING RESISTOR

(ONE RESISTOR ON EACH END)

BA

R

D

RO

DI

DE

RERE

R

RO

DE

1

2

3

4

5

6

7

8

9

10

11

12

13

14

MAX1480EA/

MAX845E

OR EQUIVALENT

DI

DE

RO

V

IN

+5V

74HC86

C1
22µF

RECEIVER OUTPUT

C2

0.1µF

DRIVER INPUT

DRIVER ENABLE

V

CC1

V

CC2

D1

D2

GND1

FS

SD

V

R1

R2

R3

CC3

V

CC4

GND2

V

CC5

DI

DE

RO

BA

D

DI

MAX1480EC

MAX487E

MAX1487E

120Ω

100Ω

AC1 (MAKE NO CONNECTION)

28

AC2 (MAKE NO CONNECTION)

27

ISO V

CC1

26

B

25

ISO RO DRV

24

A

23

ISO DI IN

22

ISO DE IN

21

ISO COM1

20

ISO DI DRV

19

ISO V

CC2

18

ISO DE DRV

17

ISO COM2

16

ISO RO LED

15

B

A

TERMINATING RESISTOR

(ONE RESISTOR ON EACH END)

R6

R4

R5

D

R

RE

B

120Ω

A

SH

DI

DE

RO

SHIELD
(OPTIONAL)

NOTE: RESISTOR R7 PROTECTS
THE MAX1480EA/MAX1480EC
FROM TRANSIENT CURRENTS
BETWEEN SHIELD AND
TRANSMISSION LINES.

R7

100Ω

LOGIC GROUND ISOLATION BARRIER ISOLATED COMMON

270pF

4kV

MAX1480E/MAX1490E

±15kV ESD-Protected, Isolated RS-485/RS-422

Data Interfaces

______________________________________________________________________________________ 17

MAX1480EC/MAX1490EA/MAX1490EB. 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 MAX1480EA/MAX1480EC/MAX1490EA/MAX1490EB
are specified and characterized using the resistor val­ues shown in Tables 1 and 2. Altering the recommend­ed values can degrade performance.

DI and DE are intended to be driven through a series
current-limiting resistor. Directly grounding these
pins destroys the device.

The DI and DE (MAX1480EA/MAX1480EC only) inputs
are the cathodes of LEDs whose anodes are connected
to the supply. These points are best driven by a CMOS­logic 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 pullup 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 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 MAX1490EA/MAX1490EB, each shield should have its
own 100Ω resistor (Figures 1, 2, 15, and 16).

Double-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 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 cur-

Figure 16. Typical Full-Duplex RS-485/RS-422 Network

CC1

1

CC2

2

D1

3

D2

4

5

FS

6

SD

7

CC3

8

DI

9

CC4

10

RO

11

12

MAX1490EA/

MAX1490EB

MAX845E

ISOLATION BARRIER

AC1 (MAKE NO CONNECTION)

24

AC2 (MAKE NO CONNECTION)

23

ISO V

CC1

22

ISO RO DRV

21

A

20

B

19

MAX488E

MAX490E

Z

18

Y

17

ISO COM1

16

ISO DI DRV

15

ISO V

CC2

14

ISO RO LED

13

270pF

4kV

V

IN

+5V

74HC86

OR EQUIVALENT

DI

RO

C1
22µF

DRIVER INPUT

RECEIVER OUTPUT

C2

0.1µF

R1

´

DI

R2

V

V

GND1

V

V

GND2

LOGIC GROUND

120Ω

120Ω

120Ω

R3

R5, 100Ω

R4

R6, 100Ω

ISOLATED COMMON

A

B

Z

Y

SH1

SH2

NOTE: RESISTORS R5 AND R6 PROTECT
THE MAX1490EA/MAX1490EB FROM TRANSIENT
CURRENTS BETWEEN SHIELD AND
TRANSMISSION LINES.

SHIELD (OPTIONAL)

120Ω

SHIELD (OPTIONAL)

Y

D

DI

Z

B

RO

R

A

MAX1480E/MAX1490E

±15kV ESD-Protected, Isolated RS-485/RS-422
Data Interfaces

18 ______________________________________________________________________________________

rents 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 17 shows a half-duplex (2-wire), bidirectional,
party-line repeater system that prevents interference
and/or damage from ground-potential differences. Two
MAX1480EA/MAX1480EC isolated RS-485 transceivers
are used to isolate each of the network segments from
the electrical environment of the repeater. The
MAX1480EA/MAX1480EC 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 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 17, 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 17 can be used either directly as
shown, with the slew-rate-limited MAX1480EC, for data
transfer rates up to 160kbps, or with the MAX1480EA for
data rates up to 2.5Mbps (see Table 1 for pullup and
LED resistor values when using the MAX1480EA). If dual­port isolation is not needed, one of the MAX1480EC
devices can be replaced by a MAX487E for 250kbps
applications.

Reliability

These products contain transformers, optocouplers, and
capacitors, in addition to several monolithic ICs and
diodes. As such, the reliability expectations more closely
represent those of discrete optocouplers rather than the
more robust characteristics of monolithic silicon ICs. The
reliability testing programs for these multicomponent
devices may be viewed on the Maxim website
(www.maxim-ic.com) under Technical Support,
Technical Reference, Multichip Products.

Figure 17. Double-Isolated RS-485 Repeater

+5V +5V

NETWORK SEGMENT A

3kΩ 3kΩ

200Ω

23

A

25

B

26

MAX1480EC MAX1480EC

3kΩ

19
22
17
21

24 24

15

2

10

8

14

13 1

9

11

5712

200Ω

200Ω

3kΩ

DRIVER
ENABLE
B > A

23

25

26

3kΩ

19
22
17
21

15

NETWORK SEGMENT B

A

B

200Ω

200Ω

2 8 10 14

9

11

5712

DRIVER
ENABLE
A > B

200Ω

3kΩ

2

74HC04

43 13

+5V

1000pF

51kΩ

16 15

2B Q

74HC123

AQ

1

14

13

4

CLR

311

+5V

1000pF51kΩ

7

BQ

10

74HC123

CLR

6

5

12AQ9

±15kV ESD-Protected, Isolated RS-485/RS-422

Data Interfaces

MAX1480E/MAX1490E

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 [phone]___________________ 19

© 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

Ordering Information (continued) Pin Configurations (continued)

†

Data rate for A parts is up to 2500kbps. Data rate for C parts is

up to 250kbps.

Selector Guide

PART

†

TEMP. RANGE PIN-PACKAGE

28 Wide Plastic DIP0°C to +70°C

MAX1480ECCPI

MAX1480ECEPI -40°C to +85°C 28 Wide Plastic DIP

24 Wide Plastic DIP0°C to +70°C

MAX1490EACPG

MAX1490EAEPG -40°C to +85°C 24 Wide Plastic DIP

24 Wide Plastic DIP0°C to +70°C

MAX1490EBCPG

MAX1490EBEPG -40°C to +85°C 24 Wide Plastic DIP

MAX1490EB Full 0.25 Yes

No2.5FullMAX1490EA

MAX1480EC Half 0.25 Yes

No2.5HalfMAX1480EA

SLEW-

RATE

LIMITED

DATA

RATE

(Mbps)

HALF/

FULL

DUPLEX

PART

This device is constructed using a unique set of packaging
techniques that impose a limit on the thermal profile the device
can be exposed to during board-level solder attach and
rework. Maxim recommends the use of the solder profiles rec­ommended in the industry-standard specification, JEDEC
020A, paragraph 7.6, Table 3 for IR/VPR and Convection
Reflow processes. Preheating, per this standard, is required.
Hand or wave soldering is not recommended.

TOP VIEW

V

V

GND1

V

V

GND2

V

CC1

CC2

CC3

CC4

CC5

1

2

3

D1

D2

4

5

FS

6

SD

7

8

9

DI

10

11

DE

12

RO

13

14

MAX1480EA/

MAX1480EC

MAX845

ISOLATION BARRIER

MAX487E

MAX1487E

DIP

28

27

26

25

24

23

22

21

20

19

18

17

16

15

AC1

AC2

ISO V

CC1

B

ISO RO DRV

A

ISO DI IN

ISO DE IN

ISO COM1

ISO DI DRV

ISO V

CC2

ISO DE DRV

ISO COM2

ISO RO LED