Datasheet

MAX3480EA/MAX3480EB
±15kV ESD-Protected, Isolated, 3.3V
RS-485/RS-422 Data Interfaces
_______________________________________________________________________________________ 9
_______________Detailed Description
The MAX3480EA/MAX3480EB are electrically isolated,
RS-485/RS-422 data-communications interface solu-
tions. Transceivers, optocouplers, a power driver, and a
transformer are in one standard 28-pin PDIP package.
Signals and power are internally transported across the
isolation barrier (Figure 1). Power is transferred from the
logic side (nonisolated side) to the isolated side of the
barrier through a center-tapped transformer. Signals
cross the barrier through high-speed optocouplers. A
single +3.3V supply on the logic side powers both
sides of the interface.
Figure 1. Block Diagram
AC1 (MAKE NO CONNECTION)
AC2 (MAKE NO CONNECTION)
SHIELD (OPTIONAL)
EXTERNAL RS-485/RS-422 WIRING
ISO V
CC1
B
D2
D1
D1, D2
1N914
V
CC2
V
CC1
ISO RO DRV
A
B
A
SH
ISO DI IN
ISO DE IN
V
CC3
SD
FS
GND1
ISO COM1
ISO DI DRV
ISO V
CC2
ISO DE DRV
GND2
DE
V
CC4
DI
ISO COM2
ISO RO LED
V
CC5
RO
R
L
R
L
R4*
R5*
R8
100Ω
BOOSTED V+
C3
0.01µF
C4
270pF
4kV
R6*
R7*
R1*
R2*
DI
´
DE´
R3*
RO
LOGIC
I/O
V
IN
+3.0V TO +3.6V
C1
22µF
C2
0.1µF
MAX3480EA/EB
LOGIC GROUND
ISOLATION BARRIER
ISOLATION COMMON
MAX845
1
2
28
27
3
4
5
6
7
8
9
10
11
12
13
14
26
25
24
23
22
21
20
19
18
17
16
15
MAX845
N
MAX3480EA: MAX485E
MAX3480EB: MAX487E
RE
ISO RO DRV
ISO DE IN
ISO DI IN
ISO COM1
ISO V
CC1
A
B
R
D
N
Q
Q
TF/F
V
CC3
FS
OSC
1.1MHz/
1.6MHz
SD
GND1
D2
D1
SHIELD (OPTIONAL)
NOTE: RESISTOR R8 PROTECTS THE
MAX3480E FROM TRANSIENT
CURRENTS BETWEEN SHIELD AND
A AND B.
TWISTED PAIR
TO OTHER TRANSCEIVERS
TERMINATING RESISTOR
(ONE RESISTOR ON EACH END)
TWISTED PAIR
TO OTHER TRANSCEIVERS
MAX1487E
MAX487E
*SEE TABLE 1.
Table 1. Pullup and LED Drive Resistors
PART R1 (Ω) R2 (Ω) R3 (Ω) R4 (Ω) R5 (Ω) R6 (Ω)
MAX3480EA 100 100 680 3600 1000 200
MAX3480EB 100 100 2000 3600 3600 200
R7 (Ω)
Open
430