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.
| PARAMETER | SYMBOL | CONDITIONS | MIN | TYP | MAX | UNITS |
| Driver Differential Output Delay | tDD | RL = 60Ω, Figure 7 | 600 | 900 | 1400 | ns |
| Driver Differential Output Transition Time | tTD | RL = 60Ω, Figure 7 | 400 | 700 | 1200 | ns |
| Driver Propagation Delay, Low-to-High Level | tPLH | RL = 27Ω, Figure 8 | 700 | 1000 | 1500 | ns |
| Driver Propagation Delay, High-to-Low Level | tPHL | RL = 27Ω, Figure 8 | 700 | 1000 | 1500 | ns |
| tPLH - tPHL| Driver Propagation Delay Skew (Note 2) | tPDS | RL = 27Ω, Figure 8 | 100 | ns |
