SLUSEW0 December   2023 UCC28750

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 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Switching Characteristics
    7. 6.7 Timing Requirements
    8. 6.8 Typical Characteristics
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Detailed Pin Descriptions
      1. 7.3.1 VDD - Input Bias
      2. 7.3.2 DRV - Gate Drive Out
      3. 7.3.3 CS - Current Sensing
      4. 7.3.4 FB - Feedback
      5. 7.3.5 FLT - Fault
      6. 7.3.6 GND - Ground Return
    4. 7.4 Feature Description
      1. 7.4.1 Soft Start
      2. 7.4.2 Control Law
      3. 7.4.3 Frequency Dithering
      4. 7.4.4 Fault Protections
        1. 7.4.4.1 VDD Overvoltage and Undervoltage Lockout
        2. 7.4.4.2 Internal Overtemperature Protection
        3. 7.4.4.3 Output Overpower Protection
        4. 7.4.4.4 Output Short-Circuit Protection
        5. 7.4.4.5 FLT Pin Protections
      5. 7.4.5 Slope Compensation
    5. 7.5 Device Functional Modes
      1. 7.5.1 Off
      2. 7.5.2 Startup
      3. 7.5.3 On
      4. 7.5.4 Fault
      5. 7.5.5 Disabled
  9. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Application
      2. 8.2.2 Design Requirements
      3. 8.2.3 Detailed Design Procedure
        1. 8.2.3.1 Input Bulk Capacitance with Minimum Bulk Voltage
        2. 8.2.3.2 Transformer Turns Ratio and Inductance
        3. 8.2.3.3 Current Sense and Slope Compensation Network
        4. 8.2.3.4 Output Capacitors
        5. 8.2.3.5 VDD Capacitance, CVDD
      4. 8.2.4 Application Performance Plots
        1. 8.2.4.1 Startup
        2. 8.2.4.2 Load Transients
        3. 8.2.4.3 Q1 Drain Voltage Evaluation
      5. 8.2.5 What to Do and What Not to Do
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Documentation Support
      1. 9.1.1 Related Documentation
    2. 9.2 Receiving Notification of Documentation Updates
    3. 9.3 Support Resources
    4. 9.4 Trademarks
    5. 9.5 Electrostatic Discharge Caution
    6. 9.6 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

7.5.4 Fault

The fault state is entered when the UCC28750 devices recognizes one of the numerous faults available, as seen in Section 7.4.4. When a fault is triggered, the device stop switching operation, and begins to sink a fault current of 350 μA. This fault current causes the VDD pin voltage to drop to the Vuvlo(off) voltage, turning off the device and resetting the fault logic states. Once the device crosses the turn on voltage, Vuvlo(on), the startup phase begins and if the fault is removed then normal operation resumes. If the device is a latched variant (UCC287501/3/5/7), then the switching operation cannot resume until the VDD pin voltage is brought below the 5 V, Vpor , power-on reset threshold. Refer to figures below for expected operation waveforms in a fault state.

To have the correctly VDD cycle as shown in the fault diagrams a restriction on the startup resistors is placed, where RSTART is the startup resistor network shown in Section 7.3.1.

Equation 4. V bulk,max I fault < R start