The MAXREFDES1160 is a 5V supplied, 2.75kVRMS, full-duplex and 500kbps isolated RS-485 module using the MAX14853. This reference design demonstrates how to build an isolated RS-485 module with a low-cost transformer to provide isolated power. A transformer from HanRun, the HR600755, is used in this design. The power supply on the reference design is derived from a single 5V source. Connect the design board to a USB port or connect an external supply from VDDA to GNDA to provide 5V power supply on the logic side (A). The integrated push-pull transformer driver and external transformer (TX1) generate an isolated supply for powering the isolated side (B) of the board.
The MAX14853 isolated RS-485/RS-422 transceiver provides 2750VRMS (60s) of galvanic isolation between the cable-side (RS-485/RS-422 driver/receiver-side) and the UART-side of the module. This device allows for robust communication up to 500kbps. The MAX14853 includes an integrated 450kHz transformer driver for power transfer to the cable-side of the transceiver using an external transformer. An integrated LDO provides a simple and space-efficient architecture for providing power to the cable-side of the IC. The MAX14853 includes one drive channel and one receive channel. The receiver is ¼-unit load, allowing up to 128 transceivers on a common bus. Integrated true fail-safe circuitry ensures a logic-high on the receiver output when inputs are shorted or open. Undervoltage lockout disables the driver when cable-side or UART-side power supplies are below functional levels. The driver outputs and receiver inputs are protected from ±35kV electrostatic discharge (ESD) to GNDB on the cable-side, as specified by the Human Body Model (HBM).
This document describes the hardware shown above. The isolated RS-485 communication module has been built and tested.