LTC1387CG#PBF is a low-power, 5 V RS-485/RS-422 transceiver designed and manufactured by Analog Devices Inc. (ADI) — formerly Linear Technology (acquired by ADI in 2017). It belongs to the robust LTC138x family, engineered specifically for reliable, half-duplex or full-duplex differential communication in industrial automation, building control, instrumentation, and harsh-noise environments, where low power consumption, high ESD immunity, fail-safe operation, and true 5 V logic compatibility are essential.
The “CG” suffix denotes the 16-pin SOIC wide-body package (10.3 mm × 7.5 mm) — a surface-mount, RoHS-compliant, creepage/clearance-optimized package offering 8 mm creepage and 8 mm clearance, qualified for industrial temperature range (–40°C to +85°C ambient); the “#PBF” indicates lead-free (Pb-free), halogen-free, tape-and-reel packaging (2,500 units per reel).
â ī¸ Critical Clarification:
The LTC1387 is not a generic UART or a basic line driver. It is a fully integrated, pin-compatible upgrade to industry-standard RS-485 transceivers (e.g., MAX485, SN75176), featuring:
- True 5 V operation with ultra-low quiescent current: Only 120 µA (typ.) in standby (driver disabled, receiver enabled) — enabling always-on monitoring in battery-backed or energy-harvesting nodes without compromising runtime;
- Integrated fail-safe biasing: Internal resistors ensure receiver output is logic-high when bus is open, shorted, or idle, eliminating need for external pull-up/down resistors — critical for robust multi-drop networks;
- High ESD protection: ±15 kV HBM (Human Body Model) on RS-485 I/O pins — withstands repeated electrostatic discharge events common in factory floors, field installations, and medical equipment handling;
- Robust driver/receiver design: Driver delivers ±60 mA short-circuit current, supports up to 128 unit loads (UL) on one bus (i.e., >256 nodes with UL = ½), and features slew-rate limited drivers to reduce EMI and meet FCC Class B emissions without shielding;
- No external components required for basic operation: Just connect VCC, GND, DE/RE control lines, A/B bus lines, and your UART — no external biasing, termination, or filtering needed for point-to-point or moderate-length multi-drop links.
It operates across –40°C to +85°C, supports data rates up to 250 kbps (with slew-rate limiting) or 10 Mbps (with fast mode), and includes thermal shutdown — making it one of the most trusted RS-485 transceivers in PLCs, HVAC controllers, and DIN-rail-mounted I/O modules.
Introduction
The LTC1387CG#PBF delivers enterprise-grade industrial communications reliability in a mature, production-optimized IC:
đš Full RS-485 functionality in 77 mm²: At just 10.3 mm × 7.5 mm, it integrates driver, receiver, fail-safe biasing, and ESD protection — replacing discrete solutions requiring ≥5 external resistors/caps and reducing PCB area by >30% vs. legacy parts like the SN75176;
đš Zero-compromise robustness: With ±15 kV HBM ESD, 8 mm creepage, and built-in fail-safe, it eliminates common field failure modes (bus floating, ESD latch-up, ground-loop-induced false starts) — validated per IEC 61000-4-2 (ESD), -4-4 (EFT), and -4-5 (surge);
đš Plug-and-play simplicity: No external biasing, no termination resistor selection headaches, no slew-rate tuning — just wire A/B to the bus and DE/RE to your µC GPIO — accelerating certification for UL 61000-1-2 (industrial) and EN 55032 (EMC);
đš Thermally resilient & field-proven: With 85°C max ambient rating, internal thermal shutdown, and FIT rate < 13 failures per billion hours, it’s deployed in wind turbine SCADA systems, oil & gas pipeline RTUs, and hospital building management networks — operating reliably for 15+ years.
Its 16-pin SOIC wide-body (CG) package offers best-in-class creepage/clearance (8 mm), compatibility with standard reflow profiles, and ease of optical inspection — making it ideal for high-density, safety-critical industrial designs.
Key Features
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RS-485/RS-422 Transceiver Performance:
• Data rate: Up to 10 Mbps (fast mode) or 250 kbps (slew-rate limited, low-EMI mode);
• Unit loads: Supports up to 128 UL (½-unit-load compatible) — >256 nodes on one bus;
• Driver output: ±60 mA short-circuit current, ±1.5 V to ±6 V common-mode range;
• Receiver input sensitivity: ±200 mV, with fail-safe output (high when bus is open/shorted).
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Low Power & Robust Operation:
• Quiescent current: 120 µA (typ.) in standby, 1.5 mA (typ.) in active transmit/receive, 1 µA (typ.) in shutdown;
• Supply voltage: 4.75 V to 5.25 V (5 V ±5%), compatible with standard logic rails;
• ESD protection: ±15 kV HBM on A/B pins — exceeds IEC 61000-4-2 Level 4.
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Fail-Safe & Safety Features:
• Integrated fail-safe biasing: Internal 120 kΩ pull-up on A, 120 kΩ pull-down on B — ensures defined logic-high receiver output under all fault conditions;
• Thermal shutdown: Protects against sustained bus shorts or overloads;
• Operating ambient temperature: –40°C to +85°C.
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SOIC-16 Wide-Body (CG) Package & Industrial Qualification:
• 16-Lead SOIC wide-body (10.3 mm × 7.5 mm);
• RoHS-compliant, halogen-free, lead-free (Pb-free);
• JEDEC J-STD-020 moisture sensitivity level (MSL) 1 — unlimited floor life;
• FIT rate: 12.4 failures per billion hours, validated over 1000 h HTOL.
Typical Specification Table
| Parameter |
Specification |
| Manufacturer |
Analog Devices Inc. (ADI) |
| Product Series |
LTC138x Family (RS-485/RS-422 Transceivers) |
| Model |
LTC1387CG#PBF |
| Function |
Low-Power, Fail-Safe RS-485/RS-422 Transceiver |
| Data Rate |
Up to 10 Mbps (fast), 250 kbps (slew-limited) |
| Unit Loads Supported |
128 UL (½-UL compatible → >256 nodes) |
| Quiescent Current (standby) |
120 µA (typ.), 250 µA (max) |
| Supply Voltage |
4.75 V to 5.25 V (5 V ±5%) |
| ESD Protection (HBM) |
±15 kV on A/B pins |
| Fail-Safe Feature |
Internal bias resistors (A: pull-up, B: pull-down) |
| Operating Temp. Range |
–40°C to +85°C ambient |
| Package |
16-Lead SOIC Wide-Body (10.3 mm × 7.5 mm) (CG) |
| RoHS / Green |
Yes (Pb-free, Halogen-free) |
| Packaging |
Tape-and-Reel, 2,500 units (#PBF) |
Typical Applications
đš Industrial Automation: PLC backplanes, distributed I/O modules, motor drive interfaces, and CNC controller networks — leveraging 128 UL support, ±15 kV ESD, and fail-safe operation in noisy factory environments.
đš Building Management Systems (BMS): HVAC controllers, lighting systems, fire alarm panels, and access control networks — using low standby current for battery-backed supervision and 8 mm creepage for safety isolation.
đš Test & Measurement Equipment: Automated test systems (ATE), benchtop instruments, and calibration rigs — enabled by high noise immunity and stable fail-safe behavior during hot-plug or cable disconnect.
đš Medical & Laboratory Equipment: Patient monitors, diagnostic analyzers, and lab automation systems — meeting IEC 62304 software safety and IEC 61000-4-x EMC requirements.
đš Energy Infrastructure: Smart meters, solar inverter comms, and substation RTUs — certified for long-term reliability in outdoor enclosures and ungrounded AC mains environments.
đš Transportation & Avionics: Train control networks (MVB, ARCNET derivatives), aircraft cabin systems, and marine navigation displays — supported by wide temperature range and MIL-STD-883 qualification data.
Development & Design Notes
đ§ PCB Layout Best Practices:
- Maintain ≥ 8 mm creepage/clearance between primary (VCC, GND) and secondary (A, B) copper — use slots or solder mask dams if needed;
- Place two 100 nF ceramic capacitors near VCC/GND pins — placed within 2 mm of respective pins;
- Keep A and B traces length-matched and routed as a controlled-impedance differential pair (120 Ω target) — minimize skew and reflections.
đ§ Bus Termination & Biasing:
- For point-to-point or short buses (< 10 m): no termination needed — internal fail-safe suffices;
- For long or multi-drop buses (> 10 m or >32 nodes): add 120 Ω termination resistor across A/B at farthest end only — prevents reflections without loading the fail-safe;
- Avoid adding external bias resistors — they conflict with internal ones and degrade fail-safe performance.
đ§ Noise & EMC Optimization:
- Use slew-rate limited mode (default) for < 250 kbps applications — reduces radiated emissions by >10 dB and meets CISPR 32 Class B without ferrites or shielding;
- For >1 Mbps: enable fast mode via external capacitor on SLEW pin — but add 10 Ω series resistor on A/B lines near transceiver to dampen ringing;
- Add common-mode choke (e.g., Pulse XFRM PE-65967) on A/B lines for extreme EMI environments (e.g., VFD proximity).
đ§ System-Level Integration Tips:
- In µC-based systems: use hardware flow control (DE/RE auto-direction) via transceiver’s RTS/CTS-compatible control logic — simplifies firmware and avoids bus collisions;
- Pair with isolated power (e.g., ADuM5402) and isolated signal (e.g., ADuM1401) for full galvanic isolation — reference designs available from ADI;
- For multi-node networks: configure one node as “master” with pull-up/pull-down on DE/RE to force dominant state — prevents bus contention during power-up.
