DescripTion

The LTC2862/LTC2863/LTC2864/LTC2865 are low power, 20Mbps or 250kbps RS485/RS422 transceivers operating on 3V to 5.5V supplies that feature ±60V overvoltage fault protection on the data transmission lines during all modes of operation, including power-down. Low EMI slew rate limited data transmission is available in a logic-selectable 250kbps mode in the LTC2865 and in 250kbps versions of the LTC2862-LTC2864. Enhanced ESD protection allows these parts to withstand ±15kV HBM on the transceiver interface pins without latchup or damage.

Extended ±25V input common mode range and full failsafe operation improve data communication reliability in electrically noisy environments and in the presence of large ground loop voltages.

 

FeaTures

Protected from Overvoltage Line Faults to ±60V

3V to 5.5V Supply Voltage

20Mbps or Low EMI 250kbps Data Rate

±15kV ESD Interface Pins, ±8kV All Other Pins

Extended Common Mode Range: ±25V

Guaranteed Failsafe Receiver Operation

High Input Impedance Supports 256 Nodes

1.65V to 5.5V Logic Supply Pin (VL) for Flexible Digital Interface (LTC2865)

MP-Grade Option Available (–55°C to 125°C)

Fully Balanced Differential Receiver Thresholds for Low Duty Cycle Distortion

Current Limited Drivers and Thermal Shutdown

Pin Compatible with LT1785 and LT1791

Available in DFN and Leaded Packages

 

applicaTions

Supervisory Control and Data Acquisition (SCADA)

Industrial Control and Instrumentation Networks

Automotive and Transportation Electronics

Building Automation, Security Systems and HVAC

Medical Equipment

Lighting and Sound System Control

 

applicaTions inForMaTion

±60V Fault Protection

The LTC2862-LTC2865 devices answer application needs for overvoltage fault-tolerant RS485/RS422 transceivers operating from 3V to 5.5V power supplies. Industrial installations may encounter common mode voltages between nodes far greater than the –7V to 12V range specified by the RS485 standards. Standard RS485 transceivers can be damaged by voltages above their typical absolute maximum ratings of –8V to 12.5V. The limited overvoltage tolerance of standard RS485 transceivers makes implementation of effective external protection networks difficult without interfering with proper data network performance within the –7V to 12V region of RS485 operation. Replacing standard RS485 transceivers with the rugged LTC2862-LTC2865 devices may eliminate field failures due to overvoltage faults without using costly external protection devices.

 

±25V Extended Common Mode Range

To further increase the reliability of operation and extend functionality in environments with high common mode voltages due to electrical noise or local ground potential differences due to ground loops, the LTC2862-LTC2865 devices feature an extended common mode operating range of –25V to 25V. This extended common mode range allows the LTC2862-LTC2865 devices to transmit and receive under conditions that would cause data errors and possible device damage in competing products.

 

±15kV ESD Protection

The LTC2862 series devices feature exceptionally robust  ESD protection. The transceiver interface pins (A,B,Y,Z) feature protection to ±15kV HBM with respect to GND without latchup or damage, during all modes of operation or while unpowered. All the other pins are protected to ±8kV HBM to make this a component capable of reliable operation under severe environmental conditions.

 

Driver

The driver provides full RS485/RS422 compatibility. When enabled, if DI is high, Y–Z is positive for the full-duplex devices (LTC2863-LTC2865) and A–B is positive for the half-duplex device (LTC2862).

When the driver is disabled, both outputs are high- impedance. For the full-duplex devices, the leakage on the driver output pins is guaranteed to be less than 30µA over the entire common mode range of –25V to 25V. On the half-duplex LTC2862, the impedance is dominated by the receiver input resistance, RIN.

 

Driver Overvoltage and Overcurrent Protection

The driver outputs are protected from short circuits to any voltage within the Absolute Maximum range of –60V to 60V. The maximum current in a fault condition is ±250mA. The driver includes a progressive foldback current limiting circuit that continuously reduces the driver current limit with increasing output fault voltage. The fault current is less than ±15mA for fault voltages over ±40V.