Datasheet
MAX1480E/MAX1490E
±15kV ESD-Protected, Isolated RS-485/RS-422
Data Interfaces
______________________________________________________________________________________ 11
MAX1480EC/MAX1490EB:
Reduced EMI and Reflections
The MAX1480EC/MAX1490EB are slew-rate-limited,
minimizing EMI and reducing reflections caused by
improperly terminated cables. Figure 11 shows both
the driver output waveform of a MAX1480EA/
MAX1490EA transmitting a 150kHz signal and the
Fourier analysis of that waveform. High-frequency har-
monics with large amplitudes are evident. Figure 12
shows the same information for the slew-rate-limited
MAX1480EC/MAX1490EB transmitting the same signal.
The high-frequency harmonics have much lower ampli-
tudes, and therefore the potential for EMI is significantly
reduced.
Driver Output Protection
There are two mechanisms to prevent excessive output
current and power dissipation caused by faults or by
bus contention. A foldback current limit on the output
stage provides immediate protection against short cir-
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
C1
22µF
C2
0.1µF
LOGIC GROUND
ISOLATION BARRIER
ISOLATED COMMON
DRIVER INPUT
RECEIVER OUTPUT
DI
RO
74HC86
OR EQUIVALENT
MAX845
N
MAX1490EA: MAX490E
MAX1490EB: MAX488E
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 MAX1490EA/MAX1490EB 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
MAX488E
MAX490E
MAX1490EA/
MAX1490EB
*SEE TABLE 2.
270 pF
4kV
Figure 2. MAX1490EA/MAX1490EB Detailed Block Diagram and Typical Application Circuit
Table 2. Pullup and LED Drive Resistors for Figure 2
MAX1490EB 200 3000 330 3000
10003301000200MAX1490EA
R4 (Ω)R3 (Ω)R2 (Ω)R1 (Ω)PART