MAX1481 Datasheet, PDF (13/16 Pages) Maxim Integrated Products – Software-Selectable, Half-/Full-Duplex, Slew-Rate-Limited, 12Mbps, RS-485/RS-422 Transceivers in uMAX Package

Software-Selectable, Half-/Full-Duplex, Slew-Rate-Limited,
12Mbps, RS-485/RS-422 Transceivers in µMAX Package
Line Length vs. Data Rate
The RS-485/RS-422 standard covers line lengths up to
4000 feet. For line lengths greater than 4000 feet, use
the repeater application shown in Figure 16.
Figures 17 and 18 show the system differential voltage
for the parts driving 4000 feet of 26AWG twisted-pair
wire into 120Ω loads.
Typical Applications
The MAX1485/MAX1486 are designed for bidirectional
data communications on multipoint bus transmission
lines. Figures 19 and 20 show typical network applica-
tions circuits. These parts can also be used as line
repeaters with cable lengths longer than 4000 feet
(Figure 16).
To minimize reflections, terminate the line at both ends
in its characteristic impedance, and keep stub lengths
off the main line as short as possible. The slew-rate-lim-
ited MAX1481/MAX1485 are more tolerant of imperfect
termination than the MAX1484/MAX1486.
20dB/div
0Hz
250kHz/div
2.5MHz
Figure 15. Driver Output Waveform and FFT Plot of
MAX1481/MAX1485 Transmitting a 20kHz Signal
RO
R
RE
DE
DI
D
H/F
A
120Ω
B
MAX1481
MAX1484
MAX1485
MAX1486
DATA IN
Z
120Ω
Y
DATA OUT
NOTE: RE ON MAX1481 AND MAX1484 ONLY.
H/F ON MAX1485 AND MAX1486 ONLY.
Figure 16. Line Repeater
MAX1481/4/5/6-fig17
DI
5V/div
MAX1481/4/5/6-fig18
DI
5V/div
V_A - V_B
4V/div
V_A - V_B
4V/div
RO
5V/div
RO
5V/div
5µs/div
1µs/div
Figure 17. MAX1481/MAX1485 System Differential Voltage at
50kHz Driving 4000 ft. of Unterminated Cable
Figure 18. MAX1484/MAX1486 System Differential Voltage at
200kHz Driving 4000 ft. of Unterminated Cable
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