CM3085E

CM3085E is a half-duplex RS-485/RS-422 transceiver comprising one bus driver and one bus receiver. The driver's slew rate limiting feature suppresses signal reflections caused by improper termination impedance matching on cables, enabling error-free data transmission up to 500kbps. For protection, a failsafe circuit ensures the receiver output remains high when the receiver inputs are open or shorted. The device provides ±15kV HBM ESD protection. Its receiver input impedance is 1/8 unit load, allowing up to 256 transceivers to be connected on the same communication bus. The receiver also features input hysteresis and filtering to improve noise rejection for slowly rising and falling differential signals. The failsafe function is achieved by setting the receiver input threshold voltages to -50mV and -200mV respectively. When the differential receiver input voltage (VA - VB) is greater than or equal to -50mV, RO outputs a logic high; when the voltage is less than or equal to -200mV, RO outputs a logic low. If all transmitters on the bus are disabled (high impedance) and the receiver inputs are open or shorted, the differential input voltage will be pulled to 0V by the termination resistors. Since the threshold voltage is -50mV, the receiver is guaranteed to output a logic high. Therefore, this device is compatible with both the failsafe function and the ±200mV EIA/TIA-485 standard without requiring additional bus pull-up and pull-down resistors. The RS-485 standard specifies a unit load input impedance of 12kΩ, with a maximum drive capability of 32 unit loads. This transceiver's receiver has a 1/8 unit load input impedance (96kΩ), allowing up to 256 transceivers to be connected on the same bus. Other transceivers on the bus may have different input impedance values; as long as the total load does not exceed 32 unit loads, normal communication is maintained.

Applications

• Battery Management Systems
• Industrial Fieldbus Communication
• Building Automation
• Security Systems
• PLC and Inverter Communication
• Water, Electric, and Gas Meters

Key features

• Polarity half-duplex transmission
• Up to 500kbps data rate
• EIA/TIA-485 compatible fail-safe mode
• Low-power mode
• Enhanced ESD protection on A/B pins
• Slew rate control for bus reflection suppression
• Wide pin and package compatibility