Key Specifications

 

The UM3487E series are +3.3V powered ±15kV ESD protected, fail-safe, hot-swappable, auto polarity reversal RS-485 transceivers. The device includes fail-safe circuitry, which guarantees a logic-high receiver output when the receiver inputs are open, shorted or idle. This means that the receiver output will be logic high if all transmitters on a terminated bus are disabled (high impedance). The UM3487E features reduced slew-rate driver that minimizes EMI and reduces reflections caused by improperly terminated cables, allowing error-free data transmission up to 500kbps. All transmitter outputs and receiver inputs are protected to ±8kV using the Human Body Model and ±15kV using the IEC61000-4-2, Air-Gap Discharge.

The UM3487E includes cable auto-invert functions that reverse the polarity of the RS485 bus pins in case the cable is misconnected. Receiver’s full fail-safe features are maintained even when the receiver polarity has been reversed.

The transceivers typically draw 300μA of supply current when unloaded, or when fully loaded with the drivers disabled. The device has a 1/8-unit-load receiver input impedance that allows up to 256 transceivers on the bus and is intended for half-duplex communications.

 

- Automatic Polarity Reversal RS-485 Transceivers

- I/O logic compatible with +5V, +3.3V & +1.8V logic

- ESD Protection for RS-485 I/O Pins

  ±15kV—IEC61000-4-2, Air-Gap Discharge

  ±8kV—IEC61000-4-2, Contact Discharge

- True Fail-Safe Receiver

- Enhanced Slew-Rate Limiting

- –7V to +12V Common-Mode Input Voltage Range

- Allows up to 256 Transceivers on the Bus

- Thermal Shutdown

- Current-Limiting for Driver Overload Protection

 

 

-Smart Meters/Automated Meter Reading Systems

-Industrial-Control Local Area Networks

-PROFIBUS® and Other RS-485 Based Field Bus Networks

-Building Lighting and Environmental Control Systems

-High Node Count RS-485 Systems

-Transceivers for EMI-Sensitive Applications

Table1. Transmitting                       

Table2. Receiving

 

H: High, L: Low, X: Do not care, Z: High impedance.

V_A: Input Voltage of RS485 Non-Inverting Bus I/O terminal, V_B: Input Voltage of RS485 Inverting Bus I/O terminal.