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STMicroelectronics ST3485ECDR
- Part No.:
- ST3485ECDR
- Manufacturer:
- STMicroelectronics
- Category:
- Drivers, Receivers, Transceivers
- Package:
- 8-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
ST3485ECDR.pdf
- Description:
- IC TRANSCEIVER HALF 1/1 8SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:5,691
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Product details
Overview
ST3485ECDR from STMicroelectronics is a half-duplex RS-485/RS-422 transceiver IC operating from a single 3.3 V supply, featuring ±15 kV IEC 61000-4-2 ESD protection on A/B bus pins, guaranteed 12 Mbps data rate, and industry-standard 75176 pinout in SO8 package. It integrates one driver and one receiver with thermal shutdown, current limiting, and high-impedance shutdown mode (1 µA max), deployed in industrial automation networks for robust differential communication over long cables.
For engineers reviewing the ST3485ECDR datasheet, ST3485ECDR pinout, ST3485ECDR application, or ST3485ECDR equivalent, key selection criteria include common-mode range (–7 to +12 V), receiver hysteresis (70 mV), driver output differential voltage (≥1.5 V into 54 Ω), logic-level interoperability with 5 V systems, and automotive-grade variants (ST3485EIY) for extended temperature operation.
Technical Context
This transceiver implements a half-duplex RS-485/RS-422 physical layer interface with integrated driver enable (DE) and receiver enable (RE) control logic. Its differential driver delivers ≥1.5 V VOD into 54 Ω loads while maintaining VOC between 3 V ±0.2 V, and the receiver detects differential inputs as low as ±200 mV with 70 mV hysteresis to reject noise.
The device enters low-power shutdown (≤1 µA ISHDN) when DE = low and RE = high, and supports up to 64 unit loads on a shared bus. Driver short-circuit current is limited to ±250 mA, and thermal shutdown forces outputs into high-impedance state during overload - both functions validated across 0°C to 70°C ambient per datasheet DS2947 Rev 12.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Data rate | Guaranteed 12 Mbps - enables high-speed industrial fieldbus links without signal integrity compromise. |
| VOD (differential output) | ≥1.5 V into 54 Ω - meets RS-485 minimum drive strength for 1200 m cable runs at full rate. |
| VTH (receiver threshold) | ±200 mV with 70 mV hysteresis - ensures reliable edge detection under noisy common-mode conditions. |
| Common-mode range | –7 V to +12 V - supports operation across electrically noisy factory floors with ground potential differences. |
| ESD protection | ±15 kV air / ±8 kV contact (IEC 61000-4-2) - eliminates need for external TVS diodes on A/B lines. |
| Shutdown current | ≤1 µA - enables ultra-low-power sleep states in battery-backed or energy-conscious nodes. |
| Supply voltage | 3.0 V to 3.6 V - compatible with modern 3.3 V FPGA/CPU I/O domains without level-shifting. |
Pinout & Package
ST3485ECDR uses an SO8 (Small Outline 8-pin) surface-mount package with standard 1.27 mm pitch and ECOPACK environmental compliance. Pin 1 is RO (Receiver Output), and the layout follows industry-standard 75176 configuration for drop-in compatibility with legacy designs.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 RO | Receiver output | Active-high CMOS output reflecting A–B polarity; high-impedance when RE = high. |
| 2 RE | Receiver enable | Active-low control: RO enabled when low; high-impedance when high - combined with DE = low triggers shutdown. |
| 3 DE | Driver enable | Active-high control: driver active when high; high-impedance when low - enables half-duplex bus arbitration. |
| 4 DI | Driver input | CMOS-compatible digital input controlling A/B differential state; interoperable with 5 V logic. |
| 5 GND | Ground reference | Signal return path for VCC and all I/O; must be low-impedance to maintain common-mode rejection. |
| 6 A | Non-inverting bus terminal | Differential driver output and receiver input; connects to RS-485 bus A line. |
| 7 B | Inverting bus terminal | Differential driver output and receiver input; connects to RS-485 bus B line. |
| 8 VCC | Power supply | 3.3 V nominal input (3.0–3.6 V); powers internal circuitry and driver stage - no charge pump required. |
Key Features
| Feature | Design Value |
|---|---|
| ESD-hardened bus interface | ±15 kV IEC 61000-4-2 air discharge on A/B pins - eliminates external protection components in most industrial enclosures. |
| True 3.3 V operation | No charge pump or external capacitors needed - simplifies PCB layout and reduces BOM count vs. 5 V RS-485 transceivers. |
| Bus node scalability | Supports up to 64 unit loads - enables large daisy-chained networks in PLC backplanes or sensor clusters. |
| Fail-safe receiver | Guaranteed high RO output with floating A/B inputs - prevents undefined logic states during cable disconnect or idle bus conditions. |
| Thermal-overload protection | Driver automatically enters high-Z state upon sustained short-circuit - prevents latch-up and board-level damage. |
Applications
| Industrial PLC Backplane | Building Automation Network |
|---|---|
|
Use Scenario: Interconnecting I/O modules across a DIN-rail mounted programmable logic controller chassis using twisted-pair wiring. IC Role / Device Role / Timing Role: Half-duplex RS-485 transceiver managing point-to-point or multi-drop serial command/response traffic between CPU and remote analog/digital modules. Use Value: –7 V to +12 V common-mode range tolerates ground shifts across distributed chassis; 12 Mbps rate supports fast scan cycle updates without bottlenecks. |
Use Scenario: Linking HVAC controllers, lighting panels, and occupancy sensors via a centralized BACnet MS/TP network. IC Role / Device Role / Timing Role: Physical layer interface converting UART signals to differential RS-485 for noise-immune communication over 100+ meter building wiring. Use Value: ±15 kV ESD protection withstands frequent human contact during commissioning; 1 µA shutdown enables maintenance-mode power savings. |
| Factory Floor Sensor Hub | Energy Meter Data Concentrator |
|
Use Scenario: Aggregating vibration, temperature, and pressure readings from dozens of industrial sensors onto a single CAN-to-RS-485 gateway. IC Role / Device Role / Timing Role: Bus transceiver enabling deterministic polling of Modbus RTU slave devices in electrically hostile motor-control environments. Use Value: Thermal shutdown prevents failure during cable shorts near high-current drives; SO8 package allows compact, automated assembly on gateway PCBs. |
Use Scenario: Collecting consumption data from 32+ smart electricity meters installed across a commercial facility using a daisy-chained RS-485 loop. IC Role / Device Role / Timing Role: Robust physical layer component supporting DLMS/COSEM protocol over long-distance, multi-node meter reading infrastructure. Use Value: 64-unit-load capability allows future expansion without hardware redesign; fail-safe receiver ensures valid idle-state logic during intermittent connectivity. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar RS-485 transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| MAX3485ESA+ | Same 3.3 V supply, 12 Mbps, SO8, but only ±12 kV HBM ESD (not IEC 61000-4-2 rated); higher typical supply current (1.8 mA vs. 1.3 mA). | Lacks certified system-level ESD immunity - may require external protection in CE-marked equipment. | Select when cost sensitivity outweighs certification requirements and board space permits minor layout adjustments. |
| SN65HVD3486DR | Identical 3.3 V, 12 Mbps, SO8, ±15 kV IEC 61000-4-2 rating, but features slew-rate limiting (max 20 Mbps) and lower VOD (1.25 V min into 54 Ω). | Better EMI performance at lower data rates; insufficient VOD margin for longest RS-485 cable runs at 12 Mbps. | Prefer for EMC-critical applications below 10 Mbps; avoid where full 12 Mbps timing margin is required over 1000 ft. |
Compared with MAX3485ESA+ and SN65HVD3486DR, ST3485ECDR uniquely combines certified IEC-level ESD immunity, full 12 Mbps VOD compliance, and sub-1 µA shutdown - making it optimal for safety-certified industrial controllers requiring zero external protection and maximum timing headroom.
Availability
ST3485ECDR is available at Aetrix Electronics and suitable for industrial PLC backplanes, building automation networks, factory floor sensor hubs, and energy meter data concentrators requiring stable component supply across extended production lifecycles.
Supply support for ST3485ECDR includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.
Manufacturer
STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing microcontrollers, power management ICs, sensors, and analog/mixed-signal products for industrial, automotive, and consumer markets.
The ST3485ECDR belongs to ST's RS-485/RS-422 transceiver product line, engineered specifically for noise-immune industrial communications with emphasis on ESD resilience, low-power operation, and seamless integration into 3.3 V embedded systems.
FAQ
Is ST3485ECDR pin-compatible with older 75176-based transceivers?
Yes - ST3485ECDR uses the industry-standard 75176 pinout (RO, RE, DE, DI, GND, A, B, VCC) and matches SO8 footprint dimensions. No PCB redesign is needed when upgrading from legacy 75176, MAX485, or SP3485 designs, provided the 3.3 V supply and logic-level compatibility are verified.
What is the maximum cable length supported at 12 Mbps?
At 12 Mbps, ST3485ECDR supports up to 15 meters of standard 120 Ω twisted-pair cable (e.g., Belden 9841) per the RS-485 standard's bandwidth-distance trade-off. For longer distances, data rate must be reduced - e.g., 1200 m is achievable at 100 kbps with proper termination and shielding.
Does ST3485ECDR require external termination resistors?
Yes - a 120 Ω termination resistor must be placed across A and B at the farthest end of the RS-485 bus to prevent signal reflections. ST3485ECDR does not integrate termination; its driver is designed to drive standard 54 Ω or 60 Ω differential loads with appropriate line impedance matching.
How does the fail-safe receiver function with open or disconnected bus lines?
When A and B are floating or unterminated, internal biasing ensures the receiver interprets the differential input as >+200 mV, forcing RO high. This defined idle state prevents spurious UART framing errors in Modbus or custom protocols - no external pull-up/pull-down resistors are required for basic fail-safe operation.
ST3485ECDR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- STMicroelectronics
- Series:
- -
- Package/Case:
- 8-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Type:
- Transceiver
- Protocol:
- RS422, RS485
- Number of Drivers/Receivers:
- 1/1
- Duplex:
- Half
- Receiver Hysteresis:
- 70 mV
- Data Rate:
- 15Mbps
- Voltage - Supply:
- 3V ~ 3.6V
- Operating Temperature:
- 0°C ~ 70°C
- Grade:
- -
- Qualification:
- AEC-Q100
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-SOIC
ST3485ECDR FAQ
1.How can I place an order for ST3485ECDR through Aetrix?
Please submit a Request for Quotation (RFQ) for ST3485ECDR on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for ST3485ECDR reliable?
The price and inventory of ST3485ECDR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for ST3485ECDR is usually 5 days.
3.What payment methods are accepted for ST3485ECDR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for ST3485ECDR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for ST3485ECDR?
ST3485ECDR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your ST3485ECDR order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for ST3485ECDR?
For technical support, including ST3485ECDR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your ST3485ECDR requirements.
6.How does Aetrix verify that ST3485ECDR is sourced from the original manufacturer or authorized distributors?
All ST3485ECDR products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that ST3485ECDR meets industry standards.
7.What is the process for return or replacement of ST3485ECDR?
All ST3485ECDR units undergo pre-shipment inspection (PSI). If there is an issue with ST3485ECDR, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The ST3485ECDR part is unused and in its original packaging.
Return procedure for ST3485ECDR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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