The wired communication standards TIA/EIA-485 and TIA/EIA-422 (also known as RS-485 and RS-422), published by the Telecommunications Industry Association/Electronic Industries Alliance (TIA/EIA), specify a technology which uses differential signaling to enable data transmission over long distances and in noisy industrial environments.
The differential signaling method offers high immunity to common-mode noise; on the twisted-pair cable recommended for use in RS-485 and RS-422 networks, most received interference is common-mode. Long transmission distances increase the scope for ground potential differences, but the standards’ wide Common-Mode Range (CMR) ensures that the network operates properly even in the presence of large common-mode voltages.
Renesas offers a wide range of RS-485 transceivers which not only meet the basic requirements for compliance with this RS-485 standard, but which also go far beyond them, offering attractive features such as integrated ESD protection, and support for high data rates.
Enhanced ESD protection
Full-featured transceivers include improved ESD protection on the bus pins. Bus pins typically connect to an exposed port at the host equipment’s housing. This exposure makes the port especially susceptible to ESD events. Connecting a charged interface cable can destroy an unprotected transceiver.
Higher differential output voltage
Some bus protocols, such as Profibus DP, use an RS-485 network for the physical layer, but operating at a higher Transmit differential output voltage of 2.1V than the ±1.5V specified in the RS-485 standard. This provides for better drive performance and higher noise immunity.
Renesas’ 5V ISL3150E family features a 2.4V minimum differential output voltage, which provides 900mV more noise immunity than standard RS-485 ICs. The 40Mbits/s ISL3159E offers a 2.1V minimum differential output voltage. These transceivers can drive more than the two terminations required by the RS-485 standard.
ISL315XE transmitters can drive the 1.5V differential output voltage specified for RS-485 into as many as eight terminations. This makes them ideal for networks with a star or other nonstandard configuration.
Over-voltage protection
Over-Voltage Protection (OVP) or fault-protected transceivers enable RS-485 bus pins to survive voltages much higher than those specified by the standard. The ISL3243XE and ISL3249XE offer OVP of up to ±60V, and a CMR up to twice as wide as that specified by the RS-485 standard.
High data-rate transceivers
Near real-time applications, such as robotics, motor control and data acquisition, require high data rates of more than 25Mbits/s to minimize latency and to increase throughput. At these very high data rates, the transceiver must be characterized by low Transmit and Receive skews to minimize duty-cycle distortion. In addition, low part-to-part skews enable high-speed parallel applications such as SCSI Fast-20 and Fast-40.
High-speed devices from Renesas offer maximum Receive and Transmit skews of 1.5ns, and maximum part-to-part skew of 4ns.
The 3V ISL3179E and 5V ISL3159E support a maximum data rate of 40Mbits/s. The 5V ISL3259E operates at up to 100Mbits/s. All parts optionally support a maximum operating temperature of 125°C to handle the high temperatures encountered in motor-control applications. They are supplied in MSOP and DFN packages for space-constrained designs. They withstand ESD strikes of ±15kV.
Additionally, the ISL3159E and ISL3259E feature a Transmit differential output voltage of >2.1V, making them ideal for use in high-speed Profibus DP networks.
