MAX1480E Datasheet, PDF (11/19 Pages) Maxim Integrated Products – 15kV ESD-Protected, Isolated RS-485/RS-422

±15kV ESD-Protected, Isolated RS-485/RS-422
Data Interfaces
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
MAX1490EA: MAX490E
MAX1490EB: MAX488E
Z
D
Y
VIN
+5V
C1
C2
22µF
0.1µF
74HC86
OR EQUIVALENT
R1*
DI
DRIVER INPUT
DI´
RECEIVER OUTPUT ^R2*
RO
*SEE TABLE 2.
VCC1 ₁
VCC2 ₂
D1 3
MAX1490EA/
MAX1490EB
24 ^{AC1 (MAKE NO CONNECTION)}
23 AC2 (MAKE NO CONNECTION)
22 ^{ISO VCC1}
EXTERNAL RS-485/RS-422 WIRING
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
RL
A
B
SHIELD (OPTIONAL)
SD ₇
VCC3 ₈
DI ₉
VCC4 ₁₀
18 ^Z
17 ^Y
16 ^{ISO COM1}
15 ^{ISO DI DRV}
Z
R_L
TWISTED PAIR
TO OTHER TRANSCEIVERS
Y
R5, 100Ω _SH1
RL
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 MAX1490EA/MAX1490EB FROM
TRANSIENT CURRENTS BETWEEN SHIELD AND
TRANSMISSION LINES.
LOGIC GROUND _{270 pF}
4kV
Figure 2. MAX1490EA/MAX1490EB Detailed Block Diagram and Typical Application Circuit
Table 2. Pullup and LED Drive Resistors for Figure 2
PART
MAX1490EA
MAX1490EB
R1 (Ω)
200
200
R2 (Ω)
1000
3000
R3 (Ω)
330
330
R4 (Ω)
1000
3000
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-
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