MAXREFDES1158: 2.75kVRMS Isolated 500kbps Half-Duplex RS-485 Transceiver Using the MAX14946
The MAXREFDES1158 is a 5V supplied, 2.75kVRMS isolated, 500kbps, RS-485 module using the MAX14946. 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 GNDA to VDDA to supply the 5V to 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 MAX14946 is an isolated RS-485/RS-422 transceiver that provides 2750VRMS (60s) of galvanic isolation between the cable side (RS-485/RS-422 driver/receiver side) and the UART side of the device. This device allows for robust communication up to 500kbps and 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 supply to the cable-side of the IC. The device includes one half-duplex driver/receiver channel. The receiver is 1/8-unit load, allowing up to 256 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 the cable-side or UART-side power supplies are below functional levels. The driver outputs/receiver inputs are protected from ±30kV electrostatic discharge (ESD) to GNDB on the cable side, as specified by the Human Body Model (HBM).
Designed, Built, Tested
This document describes the hardware shown above. The isolated RS-485 communication module has been built and tested.