SLOS580G May   2008  – March 2015 ISO15 , ISO35


  1. Features
  2. Applications
  3. Description
  4. Simplified Schematics
  5. Revision History
  6. Pin Configuration and Functions
  7. Specifications
    1. 7.1  Absolute Maximum Ratings
    2. 7.2  ESD Ratings
    3. 7.3  Recommended Operating Conditions
    4. 7.4  Thermal Information
    5. 7.5  Dissipation Ratings
    6. 7.6  Supply Current
    7. 7.7  Driver Electrical Characteristics
    8. 7.8  Receiver Electrical Characteristics
    9. 7.9  Driver Switching Characteristics
    10. 7.10 Receiver Switching Characteristics
    11. 7.11 Typical Characteristics
  8. Parameter Measurement Information
  9. Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagrams
    3. 9.3 Feature Description
      1. 9.3.1 Insulation and Safety-Related Package Characteristics
      2. 9.3.2 IEC 60664-1 Ratings Table
      3. 9.3.3 Regulatory Information
      4. 9.3.4 Safety-Limiting Values
    4. 9.4 Device Functional Modes
      1. 9.4.1 Device I/O Schematics
  10. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
      3. 10.2.3 Application Curve
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Documentation Support
      1. 13.1.1 Related Documentation
    2. 13.2 Related Links
    3. 13.3 Trademarks
    4. 13.4 Electrostatic Discharge Caution
    5. 13.5 Glossary
  14. 14Mechanical, Packaging, and Orderable Information



10 Application and Implementation


Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.

10.1 Application Information

The ISO15x and ISO35x family consists of RS-485 transceivers commonly used for asynchronous data transmissions. Full-duplex implementation requires two signal pairs (four wires), and allows each node to transmit data on one pair while simultaneously receiving data on the other pair. For half-duplex transmission there is only one pair which shared for both transmission and reception of data. To eliminate line reflections, each cable end is terminated with a termination resistor, R(T), whose value matches the characteristic impedance, Z0, of the cable. This method, known as parallel termination, allows for higher data rates over longer cable length.

10.2 Typical Application

ISO15 ISO35 ISO15M ISO35M trans_app_llse11.gifFigure 18. Half-Duplex Transceiver Configurations
ISO15 ISO35 ISO15M ISO35M typ_network_sllsei9.gifFigure 19. Typical RS-485 Network With Full-Duplex Transceivers

10.2.1 Design Requirements

RS-485 is a robust electrical standard suitable for long-distance networking that may be used in a wide range of applications with varying requirements, such as distance, data rate, and number of nodes.

Table 3. Design Parameters

Pullup and Pulldown Resistors 1 kΩ to 10 kΩ
Decoupling Capacitors 100 nF

10.2.2 Detailed Design Procedure

There is an inverse relationship between data rate and cable length, which means the higher the data rate, the shorter the cable length; and conversely, the lower the data rate, the longer the cable length. When connecting a node to the bus, the distance between the transceiver inputs and the cable trunk, known as the stub, should be as short as possible. Stubs present a nonterminated piece of bus line which can introduce reflections as the length of the stub increases. As a general guideline, the electrical length, or round-trip delay, of a stub should be less than one-tenth of the rise time of the driver. The RS-485 standard specifies that a compliant driver must be able to driver 32 unit loads (UL), where 1 unit load represents a load impedance of approximately 12 kΩ. Because these devices consists of 1/8 UL transceivers, connecting up to 256 receivers to the bus is possible.

10.2.3 Application Curve

ISO15 ISO35 ISO15M ISO35M ai_hvd12_lls505.gifFigure 20. Typical Input and Output Waveforms