MAX22028AWA+ - 3.5kVRMS Isolated RS-485/RS-422 Transceiver | Analog Devices
MPN: MAX22028AWA+ ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $5.31 | $5.31 |
| 10 | $4.95 | $49.50 |
| 100 | $4.42 | $442.00 |
| 500 | $3.89 | $1,945.00 |
| 1,000 | $3.45 | $3,450.00 |
MAX22028AWA+ Overview
What is an isolated RS-485 transceiver? An RS-485/RS-422 transceiver is a differential line driver/receiver used for robust, long-distance serial communication in noisy industrial environments. Galvanic isolation adds a high-voltage barrier (typically several kVRMS) between the UART/microcontroller side and the bus side, breaking ground loops, protecting low-voltage logic from surge events, and allowing large common-mode voltages between nodes. Isolated transceivers sit at the intersection of interface ICs and power management, and are essential building blocks in industrial fieldbus, motor control, and renewable energy systems.
The MAX22028AWA+ integrates the transformer driver, low-dropout LDO, and isolation barrier on-chip, so only a single 3.3 V supply on the UART side is needed - the cable-side power is generated internally. Maxim's AutoDirection feature eliminates the external DE/RE pin control by sensing the driver input and switching direction automatically, which simplifies firmware and reduces GPIO usage on the host MCU. Integrated protection includes +/-25 V bus fault tolerance on the RS-485 pins, hot-swap capability on the cable side, and 5.5 mm creepage for reinforced insulation per IEC 60747-17 (VDE 0884-17).
Typical applications include isolated RS-485 nodes in industrial PLCs, solar inverter monitoring, building-automation RS-485 trunks, isolated sensor interfaces, and HVAC controllers. The wide-body SOIC-8 footprint makes the part a drop-in replacement for designs previously built with a small isolated DC-DC plus an external transceiver + digital isolator stack. When designing with the MAX22028AWA+, place 100 nF X7R bypass capacitors on both VDD pins within 2 mm of the package and observe the 5.5 mm clearance requirement for end-to-end primary/secondary PCB copper. This page synthesizes distributor pricing, same-family alternatives (MAX22025-MAX22028), and design notes beyond the manufacturer datasheet.
Drop-in alternatives for MAX22028AWA+ — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with MAX22028AWA+ (same form factor and footprint) — differing in Function, Package, Data Rate (max), Duplex, Galvanic Isolation Voltage.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
MAX22027AWA+
✅ Drop-In📋 Reference alternative (not in catalog)
MAX22026AWA+
✅ Drop-In📋 Reference alternative (not in catalog)
MAX22025AWA+
✅ Drop-In✓ In Stock
$3.1 / Unit
View Datasheet →MAX22025AWA+
✅ Drop-In✓ In Stock
$3.1 / Unit
View Datasheet →MAX14882AWE+
✅ Drop-In✓ In Stock
$6.18 / Unit
View Datasheet →MAX22028AWA+ Specifications
| Function | Isolated half-duplex RS-485/RS-422 transceiver |
| Number of Drivers/Receivers | 1/1 |
| Protocol | RS-422, RS-485 |
| Duplex | Half duplex |
| Data Rate (max) | 16 Mbps |
| Galvanic Isolation Voltage | 3.5 kVRMS (60 s, per datasheet) |
| Supply Voltage (UART side) | 3.0 V to 3.6 V |
| Creepage Distance | 5.5 mm (wide-body SOIC) |
| Operating Temperature | -40C to +85C |
| Package | 8-SOIC, wide body (5.5 mm creepage) |
| Mounting Type | Surface Mount |
| AutoDirection Control | Yes (internal, no DE/RE pin required) |
| Hot-Swap Support | Yes (cable side) |
| RoHS Status | Compliant |
MAX22028AWA+ Pin Configuration
| Pin 1 | VDD1 — UART-side 3.3 V supply |
| Pin 2 | GND1 — UART-side ground (logic ground) |
| Pin 3 | DI — Driver input (UART side, TTL/CMOS) |
| Pin 4 | RO — Receiver output (UART side) |
| Pin 5 | GND2 — Cable-side ground (bus ground, isolated) |
| Pin 6 | A — RS-485/RS-422 non-inverting bus pin |
| Pin 7 | B — RS-485/RS-422 inverting bus pin |
| Pin 8 | VDD2 — Internally generated isolated cable-side supply |
Typical Applications
MAX22028AWA+ is suitable for 6 applications: Industrial PLC RS-485 Nodes, Solar Inverter Monitoring, Building Automation RS-485 Trunks, Isolated Sensor Interfaces, Motor Control Drive Communication, HVAC and Energy Management Controllers.
Industrial PLC RS-485 Nodes
The MAX22028AWA+ is well matched to isolated RS-485 nodes on industrial PLCs where 3.5 kVRMS reinforced isolation breaks ground loops between the backplane logic and field wiring. The single 3.3 V UART-side supply simplifies power design, while 16 Mbps data rate covers PROFIBUS-DP at 12 Mbps and high-speed backplane telemetry. +/-25 V bus fault tolerance protects against mis-wired field installations common in brownfield retrofits.
Recommended
Solar Inverter Monitoring
Solar inverter monitoring panels use the MAX22028AWA+ as the isolated RS-485 transceiver between the inverter power stage and the DC-side monitoring MCU. Integrated AutoDirection eliminates the DE/RE GPIO on the MCU, freeing pins for ADC channels. The 5.5 mm creepage wide-body SOIC-8 simplifies end-product IEC 62109 safety certification, and 16 Mbps bandwidth supports daisy-chained string monitoring at 1 Mbps typical while leaving headroom for service tools.
Recommended
Building Automation RS-485 Trunks
In BACnet MS-TP, Modbus RTU, and KNX-bridged RS-485 trunks, the MAX22028AWA+ provides node isolation that protects 3.3 V MCU UARTs from outdoor surge events on building wiring. The wide temperature range (-40C to +85C) covers rooftop equipment rooms, and the small SOIC-8 footprint fits inside compact wall-mount controllers. Hot-swap capability on the cable side supports live fieldbus installation and replacement.
Recommended
Isolated Sensor Interfaces
Factory floor sensors (flow, pressure, level) communicate over RS-485 to PLCs using the MAX22028AWA+ to isolate the 4-20 mA loop and high-voltage sensor excitation from the host MCU ground. The integrated cable-side LDO supplies power to the bus-side interface without an additional isolated DC-DC. This reduces sensor transmitter BOM by up to 5 components versus a discrete digital-isolator + transceiver stack.
Recommended
Motor Control Drive Communication
Variable-frequency drives and servo amplifiers use the MAX22028AWA+ on the RS-485 service/commissioning port to isolate the high-voltage DC bus from the user-facing connection. 16 Mbps supports drive firmware downloads during commissioning, while +/-25 V bus fault tolerance protects against mis-wiring during maintenance. AutoDirection simplifies hand-held service-tool firmware since no direction GPIO must be toggled.
Recommended
HVAC and Energy Management Controllers
Rooftop HVAC units and energy-management controllers use the MAX22028AWA+ for isolated Modbus RTU communication between outdoor condensing units and indoor control boards. The 5.5 mm wide-body creepage simplifies UL 1995 / IEC 60335 safety certification, and the -40C cold-start capability supports unconditioned rooftop enclosures. Internal cable-side LDO removes a discrete isolated DC-DC, cutting PCB area by roughly 50%.
Recommended
Recommended Products Summary
Engineering reference data for MAX22028AWA+ — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | MAX22027AWA+ | MAX22026AWA+ | MAX22025AWA+ | MAX14882AWE+ |
|---|---|---|---|---|---|
| Brand | Analog Devices (Maxim Integrated) | Analog Devices | Analog Devices | Analog Devices | Analog Devices |
| Package | SOIC-8 wide-body (5.5 mm creepage) | SOIC-8 wide-body (5.5 mm creepage) | SOIC-8 wide-body (5.5 mm creepage) | SOIC-8 wide-body (5.5 mm creepage) | SOIC-16 wide-body (different footprint) |
| Galvanic Isolation | 3.5 kVRMS | 3.5 kVRMS | 3.5 kVRMS | 3.5 kVRMS | 5 kVRMS |
| Protocol | RS-485 / RS-422 half duplex | RS-485 / RS-422 half duplex | RS-485 / RS-422 half duplex | RS-485 / RS-422 half duplex | RS-485 / RS-422 half duplex |
| AutoDirection | Yes | Yes | Yes | Yes | No (manual DE/RE) |
| Integrated Isolated Supply | Yes (internal DC-DC + LDO) | Yes | Yes | Yes | No (requires external isolated supply) |
| Operating Temperature | -40C to +85C | -40C to +85C | -40C to +85C | -40C to +85C | -40C to +125C |
Key Differentiators
- Integrated transformer driver + LDO eliminates external isolated DC-DC (vs MAX14882AWE+)
- AutoDirection eliminates external DE/RE pin control (vs MAX14882AWE+)
- Higher data rate (16 Mbps) vs lower-speed same-family alternatives (vs MAX22025AWA+ / MAX22027AWA+)
Design Notes
Place two 100 nF X7R 10 V bypass capacitors as close as possible (within 2 mm) to the VDD1 (pin 1) and VDD2 (pin 8) pins. Use a 4-layer PCB with continuous ground planes on layers 2 and 3 to maintain the 5.5 mm creepage/clearance requirement for reinforced isolation per IEC 60747-17. Do NOT route any UART-side signal traces between pins 5-8; treat pins 1-4 and pins 5-8 as independent islands separated by a keep-out moat under the package.
Estimated: at 16 Mbps with 5 m of CAT-5 cable, the unterminated bus can produce reflections that violate RS-485 signaling. Add 120 ohm termination resistors at both ends of the bus only when the bus is long enough for the one-way propagation delay to approach half the bit time (i.e. > ~10 m at 16 Mbps). For stub-heavy networks, bias resistors may also be needed to idle the bus high - consult the Analog Devices 'RS-485 Termination and Biasing' application guide.
Estimated: at 3.6 V VDD1 and 25 mA quiescent current typical, the MAX22028AWA+ dissipates about 90 mW internally, which produces negligible self-heating. The wide-body SOIC-8 has theta_JA around 80 C/W on a standard 4-layer JEDEC test board, so no special thermal copper pour is required. However, when the cable-side bus sustains a sustained fault (e.g. shorted to 24 V), fault current can exceed 100 mA and raise junction temperature - keep the cable-side ground return short and avoid tightly bundled power wiring near the bus pins.
Compliance Information
RoHS/REACH compliant per Analog Devices (formerly Maxim Integrated) product page. 3.5 kVRMS reinforced isolation per IEC 60747-17 (VDE 0884-17). Not AEC-Q100 qualified - this part is targeted at industrial and renewable-energy markets, not automotive.
