SLLSEY7F June   2017  – April 2020

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.          Application Diagram
      2.      ISO121x Devices Reduce Board Temperatures vs Traditional Solutions
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin Functions
    2.     Pin Functions
  6. 6 Specifications
    1. 6.1  Absolute Maximum Ratings
    2. 6.2  ESD Ratings
    3. 6.3  Recommended Operating Conditions
    4. 6.4  Thermal Information
    5. 6.5  Power Ratings
    6. 6.6  Insulation Specifications
    7. 6.7  Safety-Related Certifications
    8. 6.8  Safety Limiting Values
    9. 6.9  Electrical Characteristics—DC Specification
    10. 6.10 Switching Characteristics—AC Specification
    11. 6.11 Insulation Characteristics Curves
    12. 6.12 Typical Characteristics
  7. 7 Parameter Measurement Information
    1. 7.1 Test Circuits
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
    4. 8.4 Device Functional Modes
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Sinking Inputs
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
          1. 9.2.1.2.1 Setting Current Limit and Voltage Thresholds
          2. 9.2.1.2.2 Thermal Considerations
          3. 9.2.1.2.3 Designing for 48-V Systems
          4. 9.2.1.2.4 Designing for Input Voltages Greater Than 60 V
          5. 9.2.1.2.5 Surge, ESD, and EFT Tests
          6. 9.2.1.2.6 Multiplexing the Interface to the Host Controller
          7. 9.2.1.2.7 Status LEDs
        3. 9.2.1.3 Application Curve
      2. 9.2.2 Sourcing Inputs
      3. 9.2.3 Sourcing and Sinking Inputs (Bidirectional Inputs)
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Development Support
    2. 12.2 Documentation Support
      1. 12.2.1 Related Documentation
    3. 12.3 Related Links
    4. 12.4 Receiving Notification of Documentation Updates
    5. 12.5 Community Resource
    6. 12.6 Trademarks
    7. 12.7 Electrostatic Discharge Caution
    8. 12.8 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

9.2.1.2.1 Setting Current Limit and Voltage Thresholds

The RSENSE resistor limits the current drawn from the field input. A value of 562 Ω for RSENSE is recommended for Type 1 and Type 3 operation, and results in a current limit of 2.25 mA (typical). A value of 200 Ω for RSENSE is recommended for Type 2 operation, and results in a current limit of 6 mA (typical). In each case, a (slightly) lower value of RSENSE can be selected based on the need for a higher current limit or component availability. For more information, see the Electrical Characteristics—DC Specification table and Typical Characteristics section. A 1% tolerance is recommended on RSENSE but 5% resistors can also be used if higher variation in the current limit value is acceptable. The relationship between the RSENSE resistor and the typical current limit (IL) is given by Equation 1.

Equation 1. ISO1211 ISO1212 iso121x-current-limit-equation.gif

The RTHR resistor sets the voltage thresholds (VIL and VIH) as well as limits the surge current. A value of 1 kΩ is recommended for RTHR in Type 3 systems (maximum threshold voltage required is 11 V). A value of 2.5 kΩ is recommended for RTHR in Type 1 systems (maximum threshold voltage required is 15 V) and a value of 330 Ω is recommended for RTHR in Type 2 systems. The Electrical Characteristics—DC Specification table lists and the Typical Characteristics section describes the voltage thresholds with different values of RTHR. For other values of RTHR, derive the values through linear interpolation. Use Equation 2 and Equation 3 to calculate the values for the typical VIH values and minimum VIL values, respectively.

Equation 2. ISO1211 ISO1212 iso121x-vih-equation.gif
Equation 3. ISO1211 ISO1212 iso121x-vil-equation.gif

The maximum voltage on the SENSE pins of the ISO121x device is 60 V. However, because the RTHR resistor drops additional voltage, the maximum voltage supported at the module inputs is higher and given by Equation 4.

Equation 4. ISO1211 ISO1212 iso121x-vin-equation.gif

Use the ISO121x Threshold Calculator for 9V to 300V DC and AC Voltage Detection to estimate the values of the voltage transition thresholds, the maximum-allowed module input voltage, and module input current for the given values of the RSENSE and RTHR resistors.

A value of 0 Ω for RTHR also meets Type 1, Type 2 and Type 3 voltage-threshold requirements. The value of RTHR should be maximized for best EMC performance while meeting the desired input voltage thresholds. Because RTHR is used to limit surge current, 0.25 W MELF resistors must be used.

Figure 18 shows the typical input current characteristics and voltage transition thresholds for 562-Ω RSENSE and 1-kΩ RTHR.

ISO1211 ISO1212 D005.gifFigure 18. Transition Thresholds