Complete, Isolated, 3.3V

RS-485/RS-422 Data Interface

14

______________________________________________________________________________________

Figure 9. Typical RS-485/RS-422 Network

DI

DE

RO

B

A

R

D

RE

RO

DE

DI

R

120

Ω

D

A

B

RE

RE

DI

DE

RO

B

A

R

D

AC1 (MAKE NO CONNECTION)

AC2 (MAKE NO CONNECTION)

SHIELD

(OPTIONAL)

B

D2

D1

ISO RO DRV

A

B

A

SH

ISO DI IN

ISO DE IN

SD

FS

GND1

ISO COM1

ISO DI DRV

ISO DE DRV

DE

GND2

DI

ISO COM2

ISO RO LED

RO

R4

R7

R5

R8

100

Ω

120

Ω

R6, 200

Ω

MAX3480A/B

LOGIC GROUND

ISOLATION BARRIER

ISOLATED COMMON

TERMINATING RESISTOR

(ONE RESISTOR ON EACH END)

MAX485

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

TERMINATING RESISTOR

(ONE RESISTOR ON EACH END)

D1, D2

1N914

R1

130

Ω

R2

R3

BOOSTED V+

DRIVER INPUT

DRIVER ENABLE

3.0V to 3.6V

C1

22µF

6V

C2

0.1µF

C3

0.01

µF

16

14

12

5

7

13

15

8

2

DI

DE

RO

17

20

18

3

9

10

11

RECEIVER OUTPUT

6

4

74HC240

NOTE: RESISTOR R8

PROTECTS THE MAX3480

FROM TRANSIENT

CURRENTS BETWEEN

SHIELD AND “A” & “B”.