MAX1480A_05 Datasheet, PDF (13/21 Pages) Maxim Integrated Products – Complete, Isolated RS-485/RS-422 Data Interface

Complete, Isolated RS-485/RS-422
Data Interface
V_CC3
Q
FS
OSC
1.07MHz/
T F/F
1.45MHz
Q
MAX845
D1
N
D2 ^{ISO RO DRV}
N
ISO DI DRV
SD
GND1
R
A
B
MAX1490A: MAX490
MAX1490B: MAX488
Z
D
Y
V_IN
5V
C1
22µF
C2
0.1µF
74HC86
OR EQUIVALENT
R1
DI
DRIVER INPUT
DI´
RECEIVER OUTPUT ^R2
RO
MAX1490A/B
EXTERNAL RS-485/RS-422 WIRING
V_{CC1 1}
V_{CC2 2}
D1 3
24 ^{AC1 (MAKE NO CONNECTION)}
23 AC2 (MAKE NO CONNECTION)
22 ^{ISO VCC1}
TERMINATING RESISTOR
(ONE RESISTOR ON EACH END)
TWISTED PAIR
TO OTHER TRANSCEIVERS
D2 4
GND1 ₅
FS 6
21 ^{ISO RO DRV}
20 ^A
19 ^B
R_L
R_L
A
B
SHIELD (OPTIONAL)
SD ₇
V_{CC3 8}
DI ₉
V_{CC4 10}
18 ^Z
17 ^Y
16 ^{ISO COM1}
15 ^{ISO DI DRV}
Z
R_L
TWISTED PAIR
TO OTHER TRANSCEIVERS
Y
R5, 100Ω _SH1
R_L
R4
SH2
SHIELD (OPTIONAL)
R0 ₁₁
GND2 12
14 ^{ISO V}CC2
13 ISO RO LED ^R3
ISOLATION BARRIER
R6, 100Ω
ISOLATED COMMON
NOTE: RESISTORS R5 AND R6 PROTECT
THE MAX1490A/B FROM TRANSIENT
CURRENTS BETWEEN SHIELD AND
TRANSMISSION LINES.
LOGIC GROUND
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.
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