Driver Output Protection
Two mechanisms prevent excessive output current and
power dissipation caused by faults or by bus con-
tention. The first, a foldback current limit on the output
stage, provides immediate protection against short cir-
cuits over the whole common-mode voltage range (see
Typical Operating Characteristics
). The second, a ther-
mal shutdown circuit, forces the driver outputs into a
high-impedance state if the die temperature becomes
excessive.
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 18.
Figures 19, 20, and 21 show the system differential volt-
age for the parts driving 4000 feet of 26AWG twisted-
pair wire at 110kHz into 120Ω loads.
Typical Applications
The MAX3082E/MAX3085E/MAX3088E/MAX3089E
transceivers are designed for bidirectional data com-
munications on multipoint bus transmission lines.
Figures 22 and 23 show typical network applications
circuits. These parts can also be used as line repeaters,
with cable lengths longer than 4000 feet, as shown in
Figure 18.
To minimize reflections, the line should be terminated at
both ends in its characteristic impedance, and stub
lengths off the main line should be kept as short as
possible. The slew-rate-limited MAX3082E/MAX3085E,
and the two modes of the MAX3089E, are more tolerant
of imperfect termination.
MAX3080E–MAX3089E
±15kV ESD-Protected, Fail-Safe, High-Speed (10Mbps),
Slew-Rate-Limited RS-485/RS-422 Transceivers
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