SLUSA12G December   2009  – November 2022 UCC28C40-Q1 , UCC28C41-Q1 , UCC28C42-Q1 , UCC28C43-Q1 , UCC28C44-Q1 , UCC28C45-Q1

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and 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 Electrical Characteristics
    6. 7.6 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Detailed Pin Description
        1. 8.3.1.1 COMP
        2. 8.3.1.2 FB
        3. 8.3.1.3 CS
        4. 8.3.1.4 RT/CT
        5. 8.3.1.5 GND
        6. 8.3.1.6 OUT
        7. 8.3.1.7 VDD
        8. 8.3.1.8 VREF
      2. 8.3.2  Undervoltage Lockout
      3. 8.3.3  ±1% Internal Reference Voltage
      4. 8.3.4  Current Sense and Overcurrent Limit
      5. 8.3.5  Reduced-Discharge Current Variation
      6. 8.3.6  Oscillator Synchronization
      7. 8.3.7  Soft Start
      8. 8.3.8  Enable and Disable
      9. 8.3.9  Slope Compensation
      10. 8.3.10 Voltage Mode
    4. 8.4 Device Functional Modes
      1. 8.4.1 Normal Operation
      2. 8.4.2 UVLO Mode
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1  Custom Design With WEBENCH® Tools
        2. 9.2.2.2  Input Bulk Capacitor and Minimum Bulk Voltage
        3. 9.2.2.3  Transformer Turns Ratio and Maximum Duty CycleG
        4. 9.2.2.4  Transformer Inductance and Peak Currents
        5. 9.2.2.5  Output Capacitor
        6. 9.2.2.6  Current Sensing Network
        7. 9.2.2.7  Gate Drive Resistor
        8. 9.2.2.8  VREF Capacitor
        9. 9.2.2.9  RT/CT
        10. 9.2.2.10 Start-Up Circuit
        11. 9.2.2.11 Voltage Feedback Compensation
          1. 9.2.2.11.1 Power Stage Poles and Zeroes
          2. 9.2.2.11.2 Slope Compensation
          3. 9.2.2.11.3 Open-Loop Gain
          4. 9.2.2.11.4 Compensation Loop
      3. 9.2.3 Application Curves
      4. 9.2.4 Power Supply Recommendations
      5. 9.2.5 Layout
        1. 9.2.5.1 Layout Guidelines
          1. 9.2.5.1.1 Precautions
          2. 9.2.5.1.2 Feedback Traces
          3. 9.2.5.1.3 Bypass Capacitors
          4. 9.2.5.1.4 Compensation Components
          5. 9.2.5.1.5 Traces and Ground Planes
        2. 9.2.5.2 Layout Example
  10. 10Device and Documentation Support
    1. 10.1 Device Support
      1. 10.1.1 Development Support
        1. 10.1.1.1 Custom Design With WEBENCH® Tools
    2. 10.2 Documentation Support
      1. 10.2.1 Related Documentation
    3. 10.3 Related Links
    4. 10.4 Support Resources
    5. 10.5 Trademarks
    6. 10.6 Electrostatic Discharge Caution
    7. 10.7 Glossary
  11. 11Mechanical, Packaging, and Orderable Information

Package Options

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

8.3.1.4 RT/CT

RT/CT is the oscillator timing pin. For fixed frequency operation, set the timing capacitor charging current by connecting a resistor from VREF to RT/CT. Set the frequency by connecting timing capacitor from RT/CT to GND. For the best performance, keep the timing capacitor lead to GND as short and direct as possible. If possible, use separate ground traces for the timing capacitor and all other functions.

The UCC28C4x-Q1’s oscillator allows for operation to 1 MHz. The device uses an external resistor to set the charging current for the external capacitor, which determines the oscillator frequency. TI recommends timing resistor values from 1 kΩ to 100 kΩ and timing capacitor values from 220 pF to 4.7 nF. The UCC28C4x-Q1 oscillator is true to the curves of the original bipolar devices at lower frequencies, yet extends the frequency programmability range to at least 1 MHz. This allows the device to offer pin-to-pin capability where required, yet capable of extending the operational range to the higher frequencies. See Figure 7-1 for component values for setting the oscillator frequency.