MAX1480 Maxim, MAX1480 Datasheet - Page 12

• Manufacturer Part Number: MAX1480
• Description: Complete / Isolated RS-485/RS-422 Data Interface
• Manufacturer: Maxim

Complete, Isolated RS-485/RS-422
Data Interface
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
completely shut down these devices, use an external P-
channel MOSFET as shown in Figure 3. In normal opera-
12
RO
DI
______________________________________________________________________________________
FS
OR EQUIVALENT
V
5V
IN
74HC86
CC5
1.07MHz/
1.45MHz
RECEIVER OUTPUT
DRIVER INPUT
C1
22 F
OSC
(V
CC4
V
CC3
0.1 F
C2
T F/F
for the MAX1490A). Therefore, to
DI
´
Q
Q
R1
Table 2. Pull-Up and LED Drive Resistors
R2
SD
MAX1490A
MAX1490B
PART
LOGIC GROUND
GND1
GND2
V
V
V
V
CC1
CC2
CC4
CC3
SD
D1
D2
FS
R0
DI
MAX845
10
11
12
1
2
3
4
5
6
7
9
8
ISOLATION BARRIER
MAX1490A/B
GND1
N
N
R1 (Ω)
200
200
D1
D2
24
23
22
21
20
19
18
17
16
15
14
13
ISO RO DRV
ISO DI DRV
AC1 (MAKE NO CONNECTION)
AC2 (MAKE NO CONNECTION)
ISO RO DRV
A
B
Z
Y
ISO COM1
ISO DI DRV
ISO V
ISO RO LED
ISO V
CC2
CC1
R2 (Ω)
tion, SD is low, turning the MOSFET on and thereby pro-
viding power to all the V
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.
R3
1000
3000
MAX1490A: MAX490
MAX1490B: MAX488
R4
ISOLATED COMMON
D
R
R5, 100
R6, 100
R3 (Ω)
330
330
SH1
SH2
A
Y
B
Z
EXTERNAL RS-485/RS-422 WIRING
A
B
Z
Y
CC_
NOTE: RESISTORS R5 AND R6 PROTECT
R
L
THE MAX1490A/B FROM TRANSIENT
CURRENTS BETWEEN SHIELD AND
TRANSMISSION LINES.
pins. When SD is pulled high,
R
L
R4 (Ω)
1000
3000
TO OTHER TRANSCEIVERS
TO OTHER TRANSCEIVERS
(ONE RESISTOR ON EACH END)
TERMINATING RESISTOR
SHIELD (OPTIONAL)
SHIELD (OPTIONAL)
TWISTED PAIR
TWISTED PAIR
R
R
L
L