MAX3480A View Datasheet(PDF) - Maxim Integrated

Part Name

Description

Manufacturer

MAX3480A

Complete, Isolated, 3.3V RS-485/RS-422 Data Interface

Maxim Integrated 

Complete, Isolated, 3.3V

RS-485/RS-422 Data Interface

_______________Detailed Description

The MAX3480A/MAX3480B are electrically isolated,

RS-485/RS-422 data-communications interface solu-

tions. Transceivers, optocouplers, a power driver, and a

transformer are in one standard 28-pin DIP package.

Signals and power are internally transported across the

isolation barrier (Figure 1). Power is transferred from the

logic side (non-isolated side) to the isolated side of the

barrier through a center-tapped transformer. Signals

cross the barrier through high-speed optocouplers. A

single +3.3V supply on the logic side powers both

sides of the interface.

The MAX3480B features reduced-slew-rate drivers that

minimize EMI and reduce reflections caused by

improperly terminated cables, allowing error-free trans-

mission at data rates up to 250kbps. The MAX3480A’s

driver slew rates are not limited, allowing transmission

rates up to 2.5Mbps.

The frequency-select FS is connected to GND_ in normal

operation, which selects a switching frequency of

approximately 600kHz. Connect to high for a higher

900kHz switching frequency.

Drivers are short-circuit current limited and are protect-

ed against excessive power dissipation by thermal

VCC3

Q

FS

OSC

1.1MHz/

T F/F

1.6MHz

Q

MAX845

D1

N

D2

N

SD

GND1

ISO VCC1

ISO DI IN

ISO DE IN

MAX3480A: MAX485

MAX3480B: MAX487

B

D

A

ISO RO DRV

R

RE

ISO COM1

VIN

3.0V TO 3.6V

DI´

LOGIC

I/O

DE´

RO

C1

22µF

C2

0.1µF

BOOSTED V+

C3

0.01uF

R1

R2

R3

D1, D2

1N914

VCC1 1

VCC2 2

D1 3

D2 4

GND1 5

FS 6

SD 7

VCC3 8

DI 9

VCC4 10

DE 11

GND2 12

RO 13

VCC5 14

MAX3480A/B

MAX845

MAX485

MAX487

28 AC1 (MAKE NO CONNECTION)

27 AC2 (MAKE NO CONNECTION)

26 ISO VCC1

B

25

R7

ISO RO DRV

24

23 A

22 ISO DI IN

21 ISO DE IN

20 ISO COM1

19 ISO DI DRV

R6

200Ω

R4

R5

18 ISO VCC2

17 ISO DE DRV

16 ISO COM2

15 ISO RO LED

EXTERNAL RS-485/RS-422 WIRING

TERMINATING RESISTOR

(ONE RESISTOR ON EACH END)

TWISTED PAIR

TO OTHER TRANSCEIVERS

B

RL

SHIELD (OPTIONAL)

A

TWISTED PAIR

TO OTHER TRANSCEIVERS

SH

RL

SHIELD (OPTIONAL)

R8

100Ω

NOTE: RESISTOR R8 PROTECTS THE

MAX3480 FROM TRANSIENT

CURRENTS BETWEEN SHIELD AND

“A” & “B”.

LOGIC GROUND

ISOLATION BARRIER

ISOLATION COMMON

Figure 1. Detailed Block Diagram

_______________________________________________________________________________________ 9

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