LTC1535

PRODUCTION

Isolated RS485 Transceiver

Part Models: 4
1ku List Price: price unavailable

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Overview

UL Rated Isolated RS485: 2500V_RMS
- UL Recognized File #E151738
Eliminates Ground Loops
250kBd Maximum Data Rate
Self-Powered with 420kHz Converter
Half- or Full-Duplex
Fail-Safe Output High for Open or Shorted Receiver Inputs

Short-Circuit Current Limit
Slow Slew Rate Control
68kΩ Input Impedance Allows Up to 128 Nodes
Thermal Shutdown
8kV ESD Protection On Driver Outputs and Receiver Inputs
Available in 28-Lead SW Package

The LTC1535 is an isolated RS485 full-duplex differential line transceiver. Isolated RS485 is ideal for systems where the ground loop is broken to allow for much larger common mode voltage ranges. An internal capacitive isolation barrier provides 2500V_RMS of isolation between the line transceiver and the logic level interface. The powered side contains a 420kHz push-pull converter to power the isolated RS485 transceiver. Internal full-duplex communication occurs through the capacitive isolation barrier. The transceiver meets RS485 and RS422 requirements.

The driver and receiver feature three-state outputs, with the driver maintaining high impedance over the entire common mode range. The drivers have short-circuit current limits in both directions and a slow slew rate select to minimize EMI or reflections. The 68kΩ receiver input allows up to 128 node connections. A fail-safe feature defaults to a high output state when the receiver inputs are open or shorted.

Applications

Isolated RS485 Receiver/Driver
RS485 with Large Common Mode Voltage
Breaking RS485 Ground Loops
Multiple Unterminated Line Taps

Part Models: 4
1ku List Price: price unavailable

Documentation

ADI has always placed the highest emphasis on delivering products that meet the maximum levels of quality and reliability. We achieve this by incorporating quality and reliability checks in every scope of product and process design, and in the manufacturing process as well. "Zero defects" for shipped products is always our goal. View our quality and reliability program and certifications for more information.

Part Model	Pin/Package Drawing	Documentation	CAD Symbols, Footprints, and 3D Models
LTC1535CSW#PBF	28-Lead SOIC (Wide 0.3 Inch)	Material Declaration Reliablity Data Package Resources	Ultra Librarian SamacSys
LTC1535CSW#TRPBF	28-Lead SOIC (Wide 0.3 Inch)	Material Declaration Reliablity Data Package Resources	Ultra Librarian SamacSys
LTC1535ISW#PBF	28-Lead SOIC (Wide 0.3 Inch)	Material Declaration Reliablity Data Package Resources	Ultra Librarian SamacSys
LTC1535ISW#TRPBF	28-Lead SOIC (Wide 0.3 Inch)	Material Declaration Reliablity Data Package Resources	Ultra Librarian SamacSys

Part Models	Product Lifecycle	PCN

Aug 10, 2022 - 22_0176 Laser Top Mark Conversion for SOIC_W Packages Assembled in ADPG [PNG] and UTL
		PCN22_0176_Form Material_Report Delta Qualification Matrix
LTC1535CSW#PBF	PRODUCTION
LTC1535CSW#TRPBF	PRODUCTION
LTC1535ISW#PBF	PRODUCTION
LTC1535ISW#TRPBF	PRODUCTION

This is the most up-to-date revision of the Data Sheet.

Hardware Ecosystem

Parts	Product Life Cycle	Description
Interface Transceivers 2
LTM2881	PRODUCTION	Complete Isolated RS485/RS422 μModule Transceiver + Power
LTM2885	PRODUCTION	6500V_RMS Isolated RS485/RS422 μModule Transceiver + Power

Evaluation Kits

LTC1535 | Full Duplex, Isolated RS485 Transceiver with Slew Limiting

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Product Details

Demonstration circuit 241C showcases the LTC1535 isolated RS485 transceiver. The LTC1535 features 2,500V isolation; the “left-half” of the chip contains familiar RS485 logic functions and an isolated switching converter, and the “right-half” contains the RS485 transceiver. Both sides include a communications section to send data back and forth across the internal capacitive isolation barrier. The LTC1535 allows the user to break ground loops that cause problems in large systems, and it can also handle high common mode swings relative to ground without loss of data.

Isolation Considerations

The board, as constructed, is designed for 500V isolation, limited by the CTX02-14659 transformer. A full 3750V UL approvable transformer is also available from Coiltronics as CTX02-14608. Note that the LTC1535 meets only a 2,500V test. See the LTC1535 data sheet for additional information an other transformer options.

Logic Interface

The left-half of DC241C contains the logic interface sections. Large terminals are provided for +5V and logic ground (V_CC1 and GND1). The input current is approximately 94mA. The smaller terminals connect to RO (receiver output), RE (receiver enable), DE (driver enable), and DI (driver input). The terminals are arranged to match the LTC485 industry-standard pinout.

RS485 Interface

The right-hand side contains the isolated RS485 section. The chip is designed for full duplex operation. So the receiver input A-B and driver output Y-Z are brought out to small terminals. The receiver also has a local output RO2. Larger terminals V_CC2 and GND2 are powered from the transformer, and require no external power. They are included for the purpose of monitoring the isolated converter output.

Other DC241C Features

Both sides have green LEDs (D1, D3) for monitoring the presence of power. A 3.3k series resistor makes for dim viewing, but conserves current. For accurate power supply current measurement disable the LEDs with JP1 and JP3.

120Ω, 1/4W terminations are included. They are selected with jumpers JP4 (receiver) and JP5 (driver). Half-duplex operation is simplified by S1, which simply shorts A to Y and B to Z. Half to the left, full to the right. The driver slew rate is controlled by JP2; slow left and fast right.

Terminal block J1 is the fastest way to graft DC241C into a system. J1 requires a 2mm screw driver (Xcelite^® P3321 recommended). Xcelite R181 won’t fit no matter how hard you push.

Design files for this circuit board are available.