Complete, Isolated RS-485/RS-422
Data Interface
MAX1480A/B/C, MAX1490A/B
V
CC3
D1
N
R
D2
Q
N
ISO RO DRV
ISO DI DRV
MAX1490A: MAX490
MAX1490B: MAX488
D
SD
GND1
Y
A
B
Z
MAX845
Q
FS
OSC
1.07MHz/
1.45MHz
T F/F
MAX1490A/B
V
IN
5V
C1
22µF
C2
0.1µF
D1
V
CC1
V
CC2
1
2
3
24 AC1 (MAKE NO CONNECTION)
23 AC2 (MAKE NO CONNECTION)
22 ISO V
CC1
21 ISO RO DRV
20 A
MAX845
MAX488
MAX490
EXTERNAL RS-485/RS-422 WIRING
TERMINATING RESISTOR
(ONE RESISTOR ON EACH END)
TWISTED PAIR
TO OTHER TRANSCEIVERS
R
L
A
B
Z
Y
R5, 100Ω
R4
R6, 100Ω
R3
NOTE: RESISTORS R5 AND R6 PROTECT
THE MAX1490A/B FROM TRANSIENT
CURRENTS BETWEEN SHIELD AND
TRANSMISSION LINES.
SH1
SH2
SHIELD (OPTIONAL)
R
L
SHIELD (OPTIONAL)
TWISTED PAIR
TO OTHER TRANSCEIVERS
R
L
R
L
D2 4
GND1
5
FS 6
SD 7
74HC86
OR EQUIVALENT
DI
DRIVER INPUT
DI
´
RECEIVER OUTPUT
RO
R1
V
CC3
8
DI 9
R2
V
CC4
10
R0 11
GND2 12
19 B
18 Z
17 Y
16 ISO COM1
15 ISO DI DRV
14 ISO V
CC2
13 ISO RO LED
ISOLATION BARRIER
LOGIC GROUND
ISOLATED COMMON
Table 2. Pull-Up and LED Drive Resistors
PART
MAX1490A
MAX1490B
R1 (Ω)
200
200
R2 (Ω)
1000
3000
R3 (Ω)
330
330
R4 (Ω)
1000
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 V
CC5
(V
CC4
for the MAX1490A). Therefore, to
completely shut down these devices, use an external P-
channel MOSFET as shown in Figure 3. In normal opera-
tion, SD is low, turning the MOSFET on and thereby pro-
viding power to all the V
CC_
pins. When SD is pulled high,
the power oscillator is disabled and the switch is turned
off, disconnecting power from the DI and DE optocou-
plers. In normal operating mode, the switch carries only
the optocoupler currents, so an on-resistance of several
ohms will not significantly degrade efficiency.
13
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MAXIM [ MAXIM INTEGRATED PRODUCTS ]
