MAX3483/MAX3485/MAX3486/MAX3488/MAX3490/MAX3491
AROREDEZDI120?B3.3V-Powered, 10Mbps and Slew-Rate-Limited
True RS-485/RS-422 Transceivers
Y120?ZB120?120?YZBAYZBAADERERORDDIDYRRDDRMAX3488MAX3490MAX3491DERERODIDERERODINOTE: RE AND DE ON MAX3491 ONLY.Figure 22. MAX3488/MAX3490/MAX3491 Full-Duplex RS-485 Network
MAX3488MAX3490MAX3491AROREDEDIZRB120?DATA INDY120?DATA OUTNOTE: RE AND DE ON MAX3491 ONLY.Figure 23. Line Repeater for MAX3488/MAX3490/MAX3491
MAX3483/MAX3485/MAX3486/MAX3488/MAX3490/MAX3491
120?DIB3.3V-Powered, 10Mbps and Slew-Rate-Limited
True RS-485/RS-422 Transceivers
120?BDEDDEROREABABAADDIRRMAX3483MAX3485MAX3486DIRRDROREDDEROREDIDEROREFigure 21. MAX3483/MAX3485/MAX3486 Typical RS-485 Network
Driver Output Protection
Excessive output current and power dissipation caused by faults or by bus contention are prevented by two mechanisms. A foldback current limit on the output stage provides immediate protection against short circuits over the whole common-mode voltage range (see Typical Operating Characteristics). In addition, a thermal shut-down circuit forces the driver outputs into a high-impedance state if the die temperature rises excessively.
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, see Figure 23.
Figures 19 and 20 show the system differential voltage for parts driving 4000 feet of 26AWG twisted-pair wire at 125kHz into 120Ω loads.
Typical Applications
The MAX3483, MAX3485, MAX3486, MAX3488, MAX3490, and MAX3491 transceivers are designed for bidirectional data communications on multipoint bus transmission lines. Figures 21 and 22 show typical net-work applications circuits. These parts can also be used as line repeaters, with cable lengths longer than 4000 feet, as shown in Figure 23.
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 pos-sible. The slew-rate-limited MAX3483/MAX3488 and the partially slew-rate-limited MAX3486 are more tolerant of imperfect termination.
Propagation Delay
Figures 15–18 show the typical propagation delays. Skew time is simply the difference between the low-to-high and high-to-low propagation delay. Small driver/receiver skew times help maintain a symmetrical mark-space ratio (50% duty cycle).
The receiver skew time, |tPRLH - tPRHL|, is under 10ns (20ns for the MAX3483/MAX3488). The driver skew times are 8ns for the MAX3485/MAX3490/MAX3491, 11ns for the MAX3486, and typically under 100ns for the MAX3483/MAX3488.
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