RS485 Isolated Surge-Protected Castellated SMD Module

Overview

XT-C-485-HIA-V3/5 is an industrial isolated RS-485 half-duplex transceiver module. It turns one ordinary UART port (RX / TX) on your MCU into a galvanically isolated RS-485 bus interface with four-stage protection — all on a single 90 × 20 mm board.

At its core is the TDA51S485HC single-chip isolated transceiver: the isolated supply and the isolated signal path are integrated in one SOIC-16W package, so no external isolated DC-DC module and no optocoupler data path are needed — fewer speed bottlenecks, less drift and fewer failure points. The transceiver itself supports a 3.0–5.5 V wide input, 500 kbps and 1/8 unit load (256 nodes), and holds a defined high level when the bus is open, shorted or idle (fail-safe).

Beyond the isolated transceiver sits a complete port protection chain: gas discharge tube → bidirectional TVS → current-limiting resistors → common-mode choke, which blocks lightning-induced surges, VFD common-mode noise and wiring mistakes before they reach the transceiver. The topology follows the port protection circuit recommended in the transceiver datasheet rather than being a pile of parts.

Check before wiring

Terminate PE to earth nearby: the gas discharge tube uses PE as its discharge path; with PE floating, surge protection is noticeably weaker.
Never short the isolated-side PE to the logic-side GND: once the two share ground, the isolation is gone.
The 120 Ω termination resistor is on-board: it is only connected when the jumper is closed, and only the two physical ends of the bus should close it — keep intermediate nodes open.

Key Features

True galvanic isolation: the isolated supply and isolated signal are integrated in the TDA51S485HC; the logic side and the bus side need no common ground, with 5000 Vrms isolation withstand
Castellated SMD — and through-hole too: every pad carries both a castellated half-hole (stamp hole) at the board edge and a full plated through-hole, so you can either reflow the module flat like an SMD part or insert a 2.54 mm pin header / 5.08 mm terminal
Four-stage bus protection: 3-electrode gas discharge tube (20 kA) + bidirectional TVS + current-limiting resistors + common-mode choke
Automatic transmit/receive, zero firmware overhead: TX drives RE / DE directly through a Schmitt trigger, so half-duplex direction switching happens automatically and the software never handles direction
Switchable 120 Ω termination: connected or disconnected with an on-board jumper — no soldering iron needed during field debugging
Fail-safe biasing: on-board A pull-up / B pull-down bias keeps a defined level on an idle bus
Wide input range: 3.0 – 5.5 V, with an on-board voltage detection circuit so the isolated-side output level tracks 3.3 V / 5 V systems
Input and logic-side protection: 500 mA resettable fuse and input TVS, plus one ESD diode with RC filtering on each of RX / TX
A design you can check: schematic, recommended pad dimensions and documentation are public — verify every protection stage before you buy

What's in the Box

1 × XT-C-485-HIA-V3/5 module

Cables, enclosures and other accessories depend on the store SKU.

Applications

MCU ↔ RS-485 isolation at VFDs, servos and motor drives
Long buses with large ground potential differences: building automation, campuses, PV plants, EV charging piles
Outdoor runs exposed to lightning and surges: access control, electricity meters, street lighting, weather stations
Multi-drop networks of PLCs, instruments and sensors
Industrial control cabinet retrofits, DIY and teaching

Specifications

Parameter	Specification
Model	XT-C-485-HIA-V3/5
Isolated transceiver	TDA51S485HC (isolated supply + isolated signal, SOIC-16W)
Supply voltage	3.0 – 5.5 V (3.3 V / 5 V typical)
Supply current	27.9 mA @ 3.31 V; 22.7 mA @ 5.01 V
Logic-side interface	VIN / RX / TX / GND, 2.54 mm pin header
Bus-side interface	B / PE / A, 5.08 mm pluggable terminal block
Communication mode	RS-485 half-duplex, automatic direction control (no direction-control signal needed)
Max data rate	500 kbps
Bus load	256 nodes (1/8 unit load)
Isolation withstand	5000 Vrms
Common-mode transient immunity	150 kV/μs (typical)
Bus ESD	±15 kV contact discharge, ±8 kV HBM
Bus protection	Gas discharge tube + TVS + current-limiting resistors + common-mode choke
Surge discharge current	20 kA (8/20 μs, TR091H 3-electrode gas discharge tube)
Termination resistor	120 Ω / 1 W, on-board jumper connect/disconnect
Fail-safe biasing	On-board A pull-up / B pull-down bias resistors
Input protection	500 mA resettable fuse + TVS
Logic-side protection	One ESD diode per `RX` / `TX` (PESD5V0S1BA) + RC filter
Operating temperature	−40 ~ +125 °C
Dimensions	90 × 20 mm
Board thickness	1.6 mm

Usage Notes

Termination: the 120 Ω resistor is on-board and jumper-switchable. Close the jumper only on the two physical ends of the bus; leave intermediate nodes open.
Biasing: the module already provides A pull-up / B pull-down bias so an idle bus stays at a defined level. When you build a multi-node network, work out the parallel bias value of the whole bus.
Wiring: run A / B as a twisted pair where possible and earth the shield at a single point; keep PE and GND electrically separate.

Comparison

Feature	XT-C-485-HIA-V3/5	Typical isolated RS-485 module	Non-isolated RS-485 module
Galvanic isolation (isolated supply + isolated signal)	✅	✅	❌
Single-chip isolated transceiver (integrated isolated supply)	✅	❌	❌
Surge gas discharge tube (20 kA)	✅	❌	❌
Bus TVS clamping	✅	⚠️	❌
Common-mode choke filtering	✅	❌	❌
Jumper-selectable 120 Ω termination	✅	❌	❌
Fail-safe bias resistors	✅	⚠️	❌
Input over-current protection (resettable fuse)	✅	❌	❌

✅ Yes　⚠️ Partial　❌ No