SLLSEY2G March   2017  – August 2021 ISOW7840 , ISOW7841 , ISOW7842 , ISOW7843 , ISOW7844

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Description (continued)
  6. 6 Pin Configuration and Functions
    1.     Pin Functions
  7. 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  Power Ratings
    6. 7.6  Insulation Specifications
    7. 7.7  Safety-Related Certifications
    8. 7.8  Safety Limiting Values
    9. 7.9  Electrical Characteristics—5-V Input, 5-V Output
    10. 7.10 Supply Current Characteristics—5-V Input, 5-V Output
    11. 7.11 Electrical Characteristics—3.3-V Input, 5-V Output
    12. 7.12 Supply Current Characteristics—3.3-V Input, 5-V Output
    13. 7.13 Electrical Characteristics—5-V Input, 3.3-V Output
    14. 7.14 Supply Current Characteristics—5-V Input, 3.3-V Output
    15. 7.15 Electrical Characteristics—3.3-V Input, 3.3-V Output
    16. 7.16 Supply Current Characteristics—3.3-V Input, 3.3-V Output
    17. 7.17 Switching Characteristics—5-V Input, 5-V Output
    18. 7.18 Switching Characteristics—3.3-V Input, 5-V Output
    19. 7.19 Switching Characteristics—5-V Input, 3.3-V Output
    20. 7.20 Switching Characteristics—3.3-V Input, 3.3-V Output
    21. 7.21 Insulation Characteristics Curves
    22. 7.22 Typical Characteristics
  8. 8 Parameter Measurement Information
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Electromagnetic Compatibility (EMC) Considerations
      2. 9.3.2 Power-Up and Power-Down Behavior
      3. 9.3.3 Current Limit, Thermal Overload Protection
    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
        1. 10.2.3.1 Insulation Lifetime
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
      1. 12.1.1 PCB Material
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Device Support
      1. 13.1.1 Development Support
    2. 13.2 Documentation Support
      1. 13.2.1 Related Documentation
    3. 13.3 Related Links
    4. 13.4 Receiving Notification of Documentation Updates
    5. 13.5 Support Resources
    6. 13.6 Trademarks
    7. 13.7 Electrostatic Discharge Caution
    8. 13.8 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

9.3.2 Power-Up and Power-Down Behavior

The ISOW784x family of devices has built-in UVLO on the VCC and VISO supplies with positive-going and negative-going thresholds and hysteresis. When the VCC voltage crosses the positive-going UVLO threshold during power-up, the DC-DC converter initializes and the power converter duty cycle is increased in a controlled manner. This soft-start scheme limits primary peak currents drawn from the VCC supply and charges the VISO output in a controlled manner, avoiding overshoots. Outputs of the isolated data channels are in an indeterminate state until the VCC or VISO voltage crosses the positive-going UVLO threshold. When the UVLO positive-going threshold is crossed on the secondary side VISO pin, the feedback data channel starts providing feedback to the primary controller. The regulation loop takes over and the isolated data channels go to the normal state defined by the respective input channels or their default states. Design should consider a sufficient time margin (typically 10 ms with 10-µF load capacitance) to allow this power up sequence before valid data channels are accounted for system functionality.

When VCC power is lost, the primary side DC-DC controller turns off when the UVLO lower threshold is reached. The VISO capacitor then discharges depending on the external load. The isolated data outputs on the VISO side are returned to the default state for the brief time that the VISO voltage takes to discharge to zero.