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STMicroelectronics ST485BD
- Part No.:
- ST485BD
- Manufacturer:
- STMicroelectronics
- Category:
- Drivers, Receivers, Transceivers
- Package:
- 8-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
ST485BD.pdf
- Description:
- IC TRANSCEIVER HALF 1/1 8SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:1,713
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Product details
Overview
ST485BD from STMicroelectronics is a low-power, half-duplex RS-485/RS-422 transceiver featuring 300 µA quiescent current, ±7 V to +12 V common-mode input range, 30 ns driver propagation delay, 70 mV receiver hysteresis, and single 5 V supply operation. It integrates one driver and one receiver for bidirectional multipoint bus communication in industrial automation networks.
For engineers reviewing the ST485BD datasheet, ST485BD pinout, ST485BD application, or ST485BD equivalent, key selection criteria include bus node count (up to 64), thermal shutdown protection, 3-state driver output behavior during power-off, and SO-8 package compatibility with space-constrained PCB layouts.
Technical Context
The ST485BD implements a fail-safe receiver with differential threshold of ±0.2 V and 70 mV hysteresis to reject noise in electrically noisy environments. Its driver uses current limiting and thermal shutdown to maintain high-impedance outputs under overload or short-circuit conditions.
Control logic follows standard RS-485 half-duplex timing: DE and RE pins enable driver and receiver independently, supporting precise bus arbitration. Propagation delays (30 ns driver, ≤130 ns receiver) and skew (≤5 ns driver, 13 ns receiver) support reliable 2.5 Mbps data rates over twisted-pair cabling.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply voltage | 5 V ±5% - fixed single-supply operation eliminates need for dual-rail or LDO sequencing |
| Quiescent current | 300 µA typical - enables battery-backed or energy-harvesting systems with multi-year standby life |
| Common-mode range | –7 V to +12 V - accommodates ground potential differences across long industrial cable runs |
| Driver propagation delay | 30 ns typical - supports 2.5 Mbps signaling with margin for trace length and termination mismatch |
| Receiver hysteresis | 70 mV typical - suppresses false toggling from EMI-induced signal ringing on A/B lines |
| Short-circuit protection | Current limiting + thermal shutdown - prevents latch-up and permanent damage during bus faults |
| Bus node capacity | Up to 64 unit loads - allows scalable deployment in distributed PLC I/O networks without repeaters |
Pinout & Package
ST485BD is housed in an SO-8 surface-mount package (8-pin small outline integrated circuit) compliant with ECOPACK® environmental standards and JEDEC MS-012 specifications. Dimensions: 4.9 mm × 6.0 mm × 1.75 mm (L × W × H), pitch 1.27 mm.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 RO | Receiver output | CMOS-compatible TTL-level output driving microcontroller UART RX line |
| 2 RE | Receiver enable (active low) | Assert low to connect receiver to A/B bus; high-Z when disabled to prevent loading |
| 3 DE | Driver enable (active high) | Assert high to activate driver; low disables output and forces A/B into high-impedance state |
| 4 DI | Driver input | TTL/CMOS logic input accepting UART TX signal directly without level translation |
| 5 GND | Ground reference | Signal return path shared by driver, receiver, and internal bias circuitry |
| 6 A | Non-inverting bus terminal | Transmits/receives positive differential voltage swing; connects to bus A line |
| 7 B | Inverting bus terminal | Transmits/receives negative differential voltage swing; connects to bus B line |
| 8 VCC | Positive supply | 5 V power input with internal decoupling; requires local 100 nF ceramic capacitor |
Key Features
| Feature | Design Value |
|---|---|
| Low-power operation | 300 µA supply current enables use in always-on field devices with <10 µW idle power budget |
| Fail-safe receiver | ±0.2 V differential threshold with 70 mV hysteresis ensures defined logic state during open/short bus faults |
| Thermal shutdown | Driver automatically enters high-Z state if junction temperature exceeds safe limit, preventing thermal runaway |
| 3-state driver control | Independent DE and RE pins allow precise timing control for collision-free half-duplex bus arbitration |
| Robust ESD protection | ±15 kV HBM on A/B pins per manufacturer characterization - reduces need for external TVS diodes |
Applications
| Industrial PLC Backplane | Building Automation Network |
|---|---|
|
Use Scenario: Interconnecting I/O modules across DIN-rail-mounted PLC chassis using daisy-chained RS-485 bus. IC Role / Device Role / Timing Role: Half-duplex transceiver managing bidirectional command/response traffic between master controller and up to 64 slave nodes. Use Value: 30 ns propagation delay and ±7 V common-mode range ensure deterministic timing and noise immunity across 1200 m cable runs. |
Use Scenario: Linking HVAC controllers, lighting panels, and occupancy sensors in commercial buildings via BACnet MS/TP physical layer. IC Role / Device Role / Timing Role: RS-485 interface IC converting UART frames to differential signals compliant with ANSI/EIA-485-A. Use Value: Thermal shutdown and current limiting protect against wiring faults during installation and maintenance in live systems. |
| Energy Meter Communication | Factory Floor Sensor Hub |
|
Use Scenario: Enabling two-way AMI (Advanced Metering Infrastructure) communication between smart electricity meters and concentrators. IC Role / Device Role / Timing Role: Low-quiescent-current transceiver maintaining bus connectivity during meter sleep cycles while supporting wake-up polling. Use Value: 300 µA ICC enables >10-year battery life in backup-powered meters operating at 0.1% duty cycle. |
Use Scenario: Aggregating vibration, temperature, and pressure sensor data from legacy analog field devices onto a central SCADA gateway. IC Role / Device Role / Timing Role: RS-485 line driver/receiver providing galvanically isolated interface to ungrounded sensor transmitters. Use Value: –40 °C to +85 °C industrial temperature rating ensures reliable operation in non-climate-controlled machinery enclosures. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar RS-485 transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| MAX485ESA+ | Higher quiescent current (300 µA vs. 230 µA typ.), no thermal shutdown, same SO-8 footprint | Lacks fault protection; requires external current limiting for sustained bus shorts | Select when cost sensitivity outweighs robustness requirements and thermal events are mitigated externally |
| SN65HVD72DR | Lower propagation delay (18 ns), higher ESD rating (±16 kV), but 500 µA ICC and wider supply range (3–5.5 V) | Better suited for high-speed industrial Ethernet gateways needing faster turnaround times | Select when 2.5+ Mbps throughput and enhanced ESD immunity are prioritized over ultra-low power consumption |
Compared with MAX485ESA+ and SN65HVD72DR, ST485BD uniquely balances ultra-low ICC (300 µA), integrated thermal shutdown, and industrial temperature range in a standard SO-8 package-making it optimal for battery-assisted or thermally constrained RS-485 nodes where reliability and power efficiency are co-primary requirements.
Availability
ST485BD is available at Aetrix Electronics and suitable for industrial PLC backplanes, building automation networks, and smart energy metering systems requiring stable component supply across extended product lifecycles.
Supply support for ST485BD 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, delivering silicon solutions for automotive, industrial, and power management applications since 1987.
ST485BD belongs to the ST485 family of RS-485/RS-422 transceivers engineered specifically for robust, low-power, half-duplex communication in harsh industrial environments with wide ground potential variations.
FAQ
What is the maximum data rate supported by ST485BD?
The ST485BD supports up to 2.5 Mbps under standard load conditions (RDIF = 54 Ω, CL = 100 pF). This rating is validated across the full industrial temperature range (–40 °C to +85 °C) and assumes proper termination and controlled impedance PCB routing. Higher speeds may be achievable over shorter distances with optimized layout.
Does ST485BD require external current-limiting resistors on the A/B lines?
No. The ST485BD integrates driver current limiting and thermal shutdown circuitry, eliminating the need for external series resistors to protect against bus shorts. External termination (120 Ω across A/B at bus ends) and biasing (optional pull-up/pull-down) remain necessary for signal integrity per RS-485 standards.
Can ST485BD operate with a 3.3 V supply?
No. ST485BD is specified only for 5 V ±5% operation. Its input thresholds (VIH = 2.0 V, VIL = 0.8 V), driver output levels (VOD ≥1.5 V), and internal biasing are designed for 5 V logic compatibility. Using 3.3 V will result in undefined receiver output states and unreliable driver switching.
How does ST485BD behave when VCC is removed while the bus remains powered?
When VCC is disconnected, the driver outputs (A/B) and receiver output (RO) enter high-impedance states, preventing bus contention. The device draws no supply current, and all control inputs (DE, RE, DI) become inactive. This "power-off" behavior is explicitly guaranteed in the datasheet and critical for hot-swap-capable systems.
ST485BD Specifications
- Product attributes
- Attribute value
- Manufacturer:
- STMicroelectronics
- Series:
- -
- Package/Case:
- 8-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- Type:
- Transceiver
- Protocol:
- RS422, RS485
- Number of Drivers/Receivers:
- 1/1
- Duplex:
- Half
- Receiver Hysteresis:
- 70 mV
- Data Rate:
- 2.5Mbps
- Voltage - Supply:
- 4.75V ~ 5.25V
- Operating Temperature:
- -40°C ~ 85°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-SOIC
ST485BD FAQ
1.How can I place an order for ST485BD through Aetrix?
Please submit a Request for Quotation (RFQ) for ST485BD 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 ST485BD reliable?
The price and inventory of ST485BD are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for ST485BD is usually 5 days.
3.What payment methods are accepted for ST485BD?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for ST485BD transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for ST485BD?
ST485BD orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your ST485BD 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 ST485BD?
For technical support, including ST485BD datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your ST485BD requirements.
6.How does Aetrix verify that ST485BD is sourced from the original manufacturer or authorized distributors?
All ST485BD 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 ST485BD meets industry standards.
7.What is the process for return or replacement of ST485BD?
All ST485BD units undergo pre-shipment inspection (PSI). If there is an issue with ST485BD, 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 ST485BD part is unused and in its original packaging.
Return procedure for ST485BD:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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