HG485
Half-duplex RS-485 transceiver with 20Mbps data rate, ±15kV ESD protection, and wide common mode range
Product Overview
Description
HG485 is a robust half-duplex RS-485/RS-422 transceiver designed for industrial multi-drop communication networks.
With data rates up to 20Mbps, ±15kV ESD protection, and -7V to +12V common mode range, this transceiver provides reliable communication in harsh industrial environments.
The device features true fail-safe operation, thermal shutdown protection, and low power consumption suitable for battery-powered applications.
Product Series
HG
Primary Application
Industrial automation networks
Key Features
- High data rate up to 20Mbps
- ±15kV ESD protection on bus pins
- True fail-safe receiver (open, short, idle)
- Wide common mode range -7V to +12V
- 1/8 unit load allows 256 nodes on bus
- Thermal shutdown protection
- Low current shutdown mode
- Glitch-free power-up/power-down
Specifications
| Data Rate | Up to 20Mbps |
|---|---|
| ESD Protection | ±15kV HBM on bus pins |
| Common Mode Range | -7V to +12V |
| Differential Output | 1.5V min (54Ω load), 2.0V min (100Ω load) |
| Supply Voltage | 4.5V to 5.5V |
| Supply Current | 500μA typical (enabled), 10μA (shutdown) |
| Receiver Sensitivity | ±200mV |
| Receiver Input Impedance | 1/8 unit load (96kΩ) |
| Package | SOP-8, DIP-8 |
Applications
Industrial automation networks
Industrial automation and control
Building automation systems
Industrial automation and control
Motor control systems
Motor drive and control systems
Security and surveillance systems
Electronic system design
Point-of-sale equipment
Electronic system design
Battery-powered instruments
Battery and charging management
Remote sensor networks
Sensor signal conditioning
FAE Expert Insights
"HG485 is my recommended choice for industrial RS-485 applications. The ±15kV ESD protection eliminates the need for external protection in most applications, saving BOM cost and board space. The 1/8 unit load allows up to 256 nodes, which is much more than the standard 32 nodes. I've used this transceiver in building automation systems with cable runs over 1000 feet at 115kbps with excellent reliability. The true fail-safe feature ensures defined receiver output when the bus is idle, preventing false triggers. For best EMI performance, I recommend using shielded twisted pair cable with proper termination and grounding."
±15kV ESD protection with 256 node capability
— Michael Zhang, BeiLuo
Frequently Asked Questions
How many nodes can HG485 support on a single bus?
HG485 features 1/8 unit load receiver input impedance (96kΩ), allowing up to 256 transceivers on a single bus. Standard RS-485 transceivers have 1 unit load (12kΩ), limiting to 32 nodes. The 1/8 unit load reduces loading on the bus, allowing more nodes while maintaining signal integrity. This is particularly useful for large building automation or industrial systems. Note that cable length and data rate must still be derated appropriately for large networks.
HG485 supports large networks up to 256 nodes. Contact our FAE team for network design guidelines for large node counts.
What cable should I use for RS-485 networks?
For RS-485 networks, use twisted pair cable with 120Ω characteristic impedance. Recommended cable types: CAT5/CAT5e Ethernet cable - readily available, good for most applications; RS-485 specific cable - shielded twisted pair with 120Ω impedance; and Industrial rated cable - for harsh environments with better noise immunity. Use shielded cable in noisy environments, grounding the shield at one end only. Characteristic impedance should be 100-120Ω to match termination resistors. Avoid flat ribbon cable or untwisted wire as they lack noise immunity.
Use CAT5e or dedicated RS-485 cable with proper shielding. Our FAE team can provide cable selection and installation guidelines.
How do I terminate an RS-485 network with HG485?
Proper termination is essential for reliable RS-485 communication. Termination resistors (typically 120Ω) should be placed at both ends of the bus, matching the cable characteristic impedance. Do not place termination at intermediate nodes. For a linear bus topology, termination goes at the two furthest points. For a star topology, convert to linear or use repeaters. Stub length (distance from main bus to transceiver) should be minimized to less than 1 foot. Termination prevents signal reflections that cause data errors. Biasing resistors (pull-up to A, pull-down to B) may be needed for fail-safe operation.
Use 120Ω termination at both bus ends. Minimize stub length. Contact our FAE team for network topology guidelines.
What is the maximum data rate vs cable length for HG485?
RS-485 data rate and cable length are inversely related. At 100kbps, maximum length is approximately 4000 feet (1200m). At 1Mbps, maximum is about 400 feet (120m). At HG485's maximum 20Mbps, keep cable under 50 feet (15m). This relationship exists because higher data rates have shorter bit times, making reflections more problematic. Use high-quality twisted pair cable with 120Ω characteristic impedance. For long distances at high speeds, consider using repeaters or fiber optic converters. Always test communication at the extremes of your operating conditions.
Trade off data rate for distance. Use repeaters for long high-speed networks. Contact our FAE team for network design assistance.
How do I configure HG485 for half-duplex communication?
HG485 is a half-duplex transceiver, meaning it can transmit or receive but not both simultaneously. The DE (Driver Enable) and RE (Receiver Enable) pins control direction. For transmit: Set DE high and RE high (or RE high to disable receiver). For receive: Set DE low and RE low. In many designs, DE and RE are tied together and controlled by one GPIO: High = transmit, Low = receive. Add a delay (one bit time) after enabling driver before sending data, and after last bit before disabling driver. This prevents truncating the message. Microcontroller UARTs often have automatic direction control features.
Control DE/RE pins for direction. Add delays around transmission. Contact our FAE team for half-duplex software design.