Complete, Isolated RS-485/RS-422
Data Interface
V
CC3
D1
MAX845
Q
N
OSC
1.07MHz/
1.45MHz
A
R
T
F/F
FS
ISO RO DRV
ISO DI DRV
D2
B
Z
Q
MAX1490A: MAX490
MAX1490B: MAX488
N
D
Y
SD
GND1
MAX1490A/B
EXTERNAL RS-485/RS-422 WIRING
V
IN
5V
V
V
TERMINATING RESISTOR
(ONE RESISTOR ON EACH END)
CC1
CC2
AC1 (MAKE NO CONNECTION)
AC2 (MAKE NO CONNECTION)
1
2
C1
C2
24
23
22
21
20
19
18
17
16
15
14
13
22µF
0.1µF
TWISTED PAIR
TO OTHER TRANSCEIVERS
ISO V
CC1
D1
D2
3
ISO RO DRV
R
4
R
L
L
GND1
A
B
Z
Y
A
B
5
SHIELD (OPTIONAL)
FS
6
TWISTED PAIR
TO OTHER TRANSCEIVERS
Z
SD
7
R
L
74HC86
OR EQUIVALENT
V
Y
CC3
8
R
L
R1
R5, 100Ω
R6, 100Ω
SH1
DI
DRIVER INPUT
ISO COM1
ISO DI DRV
DI
9
R4
V
DI´
SHIELD (OPTIONAL)
CC4
SH2
10
11
12
R2
RECEIVER OUTPUT
ISO V
CC2
R0
RO
R3
ISO RO LED
GND2
NOTE: RESISTORS R5 AND R6 PROTECT
THE MAX1490A/B FROM TRANSIENT
CURRENTS BETWEEN SHIELD AND
TRANSMISSION LINES.
ISOLATION BARRIER
LOGIC GROUND
ISOLATED COMMON
Table 2. Pull-Up and LED Drive Resistors
PART
R1 (Ω)
R2 (Ω)
R3 (Ω)
R4 (Ω)
1000
MAX1490A
200
1000
330
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.
tion, SD is low, turning the MOSFET on and thereby pro-
viding power to all the V 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.
CC_
The high-speed optocouplers on the MAX1480A/
MAX1480C/MAX1490A consume an additional 10mA
through V
(V
for the MAX1490A). Therefore, to
CC4
CC5
completely shut down these devices, use an external P-
channel MOSFET as shown in Figure 3. In normal opera-
______________________________________________________________________________________ 13
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
