Datasheet
MAX1480A/B/C, MAX1490A/B
Complete, Isolated RS-485/RS-422
Data Interface
______________________________________________________________________________________ 13
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.
SHIELD (OPTIONAL)
EXTERNAL RS-485/RS-422 WIRING
A
R
L
R
L
B
Z
Y
R
L
R
L
R3
R4
R5, 100Ω
SH1
SH2
R1
R2
R6, 100Ω
DI
´
V
IN
5V
22μF 0.1μF
C1 C2
MAX1490A/B
LOGIC GROUND
ISOLATION BARRIER ISOLATED COMMON
DRIVER INPUT
RECEIVER OUTPUT
DI
RO
74HC86
OR EQUIVALENT
MAX845
N
MAX1490A: MAX490
MAX1490B: MAX488
ISO DI DRV
ISO RO DRV
A
B
Z
Y
D
R
N
Q
Q
T F/F
V
CC3
FS
OSC
1.07MHz/
1.45MHz
SD GND1
D2
D1
SHIELD (OPTIONAL)
NOTE: RESISTORS R5 AND R6 PROTECT
THE MAX1490A/B FROM TRANSIENT
CURRENTS BETWEEN SHIELD AND
TRANSMISSION LINES.
TWISTED PAIR
TO OTHER TRANSCEIVERS
TERMINATING RESISTOR
(ONE RESISTOR ON EACH END)
TWISTED PAIR
TO OTHER TRANSCEIVERS
24
23
22
21
20
19
18
17
1
2
3
4
5
6
7
8
AC1 (MAKE NO CONNECTION)
AC2 (MAKE NO CONNECTION)
ISO V
CC1
ISO RO DRV
D2
D1
V
CC2
V
CC1
A
B
Z
Y
V
CC3
SD
FS
GND1
16
15
14
13
9
10
11
12
ISO COM1
ISO DI DRV
ISO V
CC2
ISO RO LED
GND2
R0
V
CC4
DI
MAX845
MAX488
MAX490
Figure 2. MAX1490A/MAX1490B Detailed Block Diagram and Typical Application Circuit
Table 2. Pull-Up and LED Drive Resistors
1000
3000
R2 (Ω)
1000
3000
R4 (Ω)
330
330
R3 (Ω)
200MAX1490A
200MAX1490B
R1 (Ω)PART