The THVD14xx family of transceivers has been designed to work in a range of applications, facilitating the transfer of data over relatively long distances while maintaining immunity against the electromagnetic noise present in many industrial applications. Different variants within this family can be selected based on particular applications needs ranging from different pin outs, half/full-duplex, data rates, loading characteristics, ESD protections and more. All devices in this family can work with supply voltages between 3.0 and 5.5 volts.
All of these devices operate within the standard set by TIA and EIA for RS-485 transceivers which specifies features such as signal amplitude, input sensitivity, and input impedance. However, several characteristics such as cable length, cable type, connectors, data rates, and bus topologies are not defined by the standard. This document’s purpose is to provide a reference to tests in a controlled environment to help system designers understand how the factors of cable length and data rate can affect data integrity and provide insight so educated design decisions can be made.
Two devices were used in this series of tests. The THVD1450 is a high speed variant which supports data rates up to 50 Mbps. The THVD1429 has similar operating characteristics to the THVD1450 with the notable inclusion of an integrated TVS diode for increased ESD protection. This TVS diode adds some amount of capacitance for each node and therefore is only specified to operate at data rates up to 20 Mbps. These two devices were tested and the results compared to observe the effect that added loading on the bus can have on the capabilities of the system.