MAX3480A データシートの表示（PDF） - Maxim Integrated
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MAX3480A Datasheet PDF : 16 Pages
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Complete, Isolated, 3.3V
RS-485/RS-422 Data Interface
shutdown circuitry that puts the driver outputs into a
high-impedance state. The receiver input has a fail-safe
feature that guarantees a logic-high output if the input
is open circuit.
The driver outputs are enabled by bringing DE´ high.
Driver-enable times are typically 200ns for the
MAX3480A and 50µs for the MAX3480B. Allow time for
the devices to be enabled before sending data. When
enabled, driver outputs function as line drivers. Driver
outputs are high impedance when DE´ is low. While
outputs are high impedance, they function as line
receivers.
The MAX3480A/MAX3480B typically withstand
1600VRMS (1 minute) or 2000VRMS (1 second). The iso-
lated outputs of these devices meet all RS-485/RS-422
specifications. The logic inputs can be driven from any
TTL/CMOS-logic family with a series resistor, and the
received data output can directly drive any of the
TTL/CMOS-logic families with only a resistive pull-up.
Boost Voltage
The MAX3480 requires external diodes on the primary
of the transformer to develop the boost voltage for the
power oscillator. In normal operation, whenever one of
the oscillator outputs (D1 and D2) goes low, the other
VIN
3.0V TO 3.6V C1
C2
74HC240 4
6
DI 2 18
8
DE 17 3
15
13
20
RO 9
11
10
22µF
6V
16
0.1µF
BOOSTED V+
C3
0.01µF
14
12 DRIVER INPUT
R1
5
DRIVER ENABLE
7
R2
RECEIVER OUTPUT
R3
D1, D2
1N914
VCC1 1
VCC2 2
D1 3
D2 4
GND1 5
FS 6
SD 7
VCC3 8
DI 9
VCC4 10
DE 11
GND2 12
RO 13
VCC5 14
LOGIC GROUND
MAX3480A/B
MAX845
MAX485
MAX487
28 AC1 (MAKE NO CONNECTION)
27 AC2 (MAKE NO CONNECTION)
26 ISO VCC1
B
25
24 ISO RO DRV
R7
23 A
22 ISO DI IN
21 ISO DE IN
20 ISO COM1
19 ISO DI DRV
R6
200Ω
R4
R5
18 ISO VCC2
17 ISO DE DRV
16 ISO COM2
15 ISO RO LED
EXTERNAL RS-485/RS-422 WIRING
TERMINATING RESISTOR
(ONE RESISTOR ON EACH END)
TWISTED PAIR
TO OTHER TRANSCEIVERS
B
RL
SHIELD (OPTIONAL)
A
TWISTED PAIR
TO OTHER TRANSCEIVERS
SH
RL
SHIELD (OPTIONAL)
NOTE: RESISTOR R8 PROTECTS
R8
THE MAX3480 FROM TRANSIENT
100
CURRENTS BETWEEN SHIELD AND
“A” & “B”.
ISOLATION BARRIER
ISOLATION COMMON
Table 1. Pull-Up and LED Drive Resistors
PART
R1 (Ω)
R2 (Ω)
R3 (Ω)
MAX3480A
150
130
680
MAX3480B
130
330
2000
R4 (Ω)
3000
2200
R5 (Ω)
1000
3000
R6 (Ω)
200
200
Figure 2. Typical Application Circuit
10 ______________________________________________________________________________________
R7 (Ω)
Open
470
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