Renesas' history with RS-232 and RS-485/422 transceivers dates back to the 1970s and we are still a market leader today. Whether it is a basic, low cost product or an enhanced product with added features, we have what our customers need for their next design.
Full-featured transceivers include improved ESD protection on bus pins that connect to an exposed port on a piece of equipment. Exposure makes the port susceptible to ESD events. Even connecting a charged interface cable could destroy an unprotected transceiver.
ESD protection falls under two standards: Human Body Model (HBM) standard and the IEC 61000-4-2 (IEC). The HBM test emulates the types of ESD events seen during manufacturing and handling, while the IEC ESD test is an end equipment test intended to harden equipment to ESD events seen in the field.
The special ESD structures utilized in Renesas' full-featured families allow these transceivers to meet the highest level for each of the standards.
Overvoltage protected, or fault protected, transceivers are designed so that the RS-485 bus pins can handle voltages much higher than those required by the RS-485 standard. This protects the device when power is routed in the same conduit as the data cable.
Intersil devices also feature a wide common mode voltage range (CMR) to compensate for the common mode voltage pick-up that occurs in long networks and noisy environments.
The ±16.5kV HBM ESD, the OVP and wide CMR features combined make the Renesas devices some of the most robust transceivers available.
Applications like robotics, motor control and data acquisition require high data rates for minimal latency and increased throughput. Renesas' full-featured, high-speed family specifies the maximum Rx and Tx skews at 1.5ns and the maximum part-to-part skew at 4ns.
Most current-generation RS-485 families have a “hot plug” function that disables the device when Vcc drops considerably below its nominal voltage (e.g., at 2.5V for Vcc = 3.3V), so 2.5V or 1.8V applications require ICs specifically designed for those operating voltages.
Power-critical applications such as remote sensor links and battery-operated security systems benefit from this level of performance.
Short, simple, low-node-count networks can often use low-cost RS-485 transceivers.
Many applications need both an RS-232 and RS-485 serial port. The dual-protocol devices integrate both transceivers into a single package. The single-channel device can be programmed for either interface. The two-channel configuration is very flexible as each channel can be either port.
Both 3.3V and 5V supply options are available. An in-line package and a more compact QFN package are available. The QFN package has additional features including a logic supply pin (VL) and selectable RS-485 data rates. The RS-232 data rate can operate up to 400kbps.
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This introduction to high-speed RS-485 designs will introduce you to standard and high-speed RS-485 networks, discuss signal degradation on the bus, review key transceiver requirements for high-speed transmission and give you some design tips for system and bus node designs as well as general high-speed design guidelines.