3.3V-Powered, 10Mbps and Slew-Rate-Limited

True RS-485/RS-422 Transceivers

General Description

The MAX3483, MAX3485, MAX3486, MAX3488, MAX3490, and MAX3491 are 3.3V, low-power transceivers for RS-485 and RS-422 communication. Each part contains one driver and one receiver. The MAX3483 and MAX3488 feature slew-rate-limited drivers that minimize EMI and reduce reflections caused by improperly terminated cables, allowing error-free data transmission at data rates up to 250kbps. The partially slew-rate-limited MAX3486 transmits up to 2.5Mbps. The MAX3485, MAX3490, and MAX3491 transmit at up to 10Mbps. Drivers are short-circuit current limited and are protected against excessive power dissipation by thermal shutdown circuitry that places the driver outputs into a high-impedance state. The receiver input has a fail-safe feature that guarantees a logic-high output if both inputs are open circuit. The MAX3488, MAX3490, and MAX3491 feature fullduplex communication, while the MAX3483, MAX3485, and MAX3486 are designed for half-duplex communication.

Applications

Low-Power RS-485/RS-422 Transceivers Telecommunications Transceivers for EMI-Sensitive Applications Industrial-Control Local Area Networks

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 shutdown circuit forces the driver outputs into a high-impedance state if the die temperature rises excessively.

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.