SLLSFS9D September   2023  – December 2024 ISOM8110 , ISOM8111 , ISOM8112 , ISOM8113 , ISOM8115 , ISOM8116 , ISOM8117 , ISOM8118

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison
  6. 5 Pin Configuration and Functions
  7. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Thermal Information
    4. 6.4 Insulation Specifications
    5. 6.5 Safety-Related Certifications
    6. 6.6 Safety Limiting Values
    7. 6.7 Electrical Characteristics
    8. 6.8 Switching Characteristics
    9. 6.9 Typical Characteristics
  8. 7 Parameter Measurement Information
  9. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
    4. 8.4 Device Functional Modes
  10. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Typical Application
        1. 9.1.1.1 Design Requirements
        2. 9.1.1.2 Detailed Design Procedure
          1. 9.1.1.2.1 Sizing RPULLUP
          2. 9.1.1.2.2 Sizing RIN
        3. 9.1.1.3 Application Curves
    2. 9.2 Power Supply Recommendations
    3. 9.3 Layout
      1. 9.3.1 Layout Guidelines
      2. 9.3.2 Layout Example
      3. 9.3.3 Reflow Profile
  11. 10Device and Documentation Support
    1. 10.1 Documentation Support
      1. 10.1.1 Related Documentation
    2. 10.2 Receiving Notification of Documentation Updates
    3. 10.3 Support Resources
    4. 10.4 Trademarks
    5. 10.5 Electrostatic Discharge Caution
    6. 10.6 Glossary
  12. 11Revision History
  13. 12Mechanical, Packaging, and Orderable Information
9.1.1.2.2 Sizing RIN

The input side of ISOM811x is current-driven. To limit the amount of current flowing into the AN pin, placing a series resistor, RIN, in series with the input as shown in Figure 9-1 is recommended.

Depending on how the ISOM811x device is being used, the value of RIN can vary quite a bit. However, at a high level, to make sure the input does not get damaged, the minimum value of RIN can be calculated for a given input voltage, VIN, in Equation 3:

Equation 3. R I N >   V I N -   V F I C ( M A X )

However, in the use case of a feedback loop, RIN directly affects the mid-band gain of the loop. Assuming that the TL431 has been configured to give a reference voltage, VREF, of 2.5V and RPULLUP is 5kΩ, Equation 4 is used to calculate the maximum value of RIN verifying that the VCOMP voltage on the primary side can be pulled to the saturation voltage of the ISOM811x, VCE(SAT).

Equation 4. R I N <   ( V O U T -   V R E F - V F )   ×   R P U L L U P   × C T R M I N V P U L L U P   -   V C E ( S A T )   =   ( 5 V -   2.5 V - 1.2 V )   ×   5 k Ω   × 100 % 10 V   -   0.3 V   =   670 Ω