SLUSEI6 November   2021 UCC28781-Q1

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and 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 Electrical Characteristics
    6. 6.6 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Detailed Pin Description
      1. 7.3.1  BUR Pin (Programmable Burst Mode)
      2. 7.3.2  FB Pin (Feedback Pin)
      3. 7.3.3  REF Pin (Internal 5-V Bias)
      4. 7.3.4  VDD Pin (Device Bias Supply)
      5. 7.3.5  P13 and SWS Pins
      6. 7.3.6  S13 Pin
      7. 7.3.7  IPC Pin (Intelligent Power Control Pin)
      8. 7.3.8  RUN Pin (Driver and Bias Source for Isolator)
      9. 7.3.9  PWMH and AGND Pins
      10. 7.3.10 PWML and PGND Pins
      11. 7.3.11 SET Pin
      12. 7.3.12 RTZ Pin (Sets Delay for Transition Time to Zero)
      13. 7.3.13 RDM Pin (Sets Synthesized Demagnetization Time for ZVS Tuning)
      14. 7.3.14 XCD Pin
      15. 7.3.15 CS, VS, and FLT Pins
    4. 7.4 Device Functional Modes
      1. 7.4.1  Adaptive ZVS Control with Auto-Tuning
      2. 7.4.2  Dead-Time Optimization
      3. 7.4.3  EMI Dither and Dither Fading Function
      4. 7.4.4  Control Law Across Entire Load Range
      5. 7.4.5  Adaptive Amplitude Modulation (AAM)
      6. 7.4.6  Adaptive Burst Mode (ABM)
      7. 7.4.7  Low Power Mode (LPM)
      8. 7.4.8  First Standby Power Mode (SBP1)
      9. 7.4.9  Second Standby Power Mode (SBP2)
      10. 7.4.10 Startup Sequence
      11. 7.4.11 Survival Mode of VDD (INT_STOP)
      12. 7.4.12 System Fault Protections
        1. 7.4.12.1  Brown-In and Brown-Out
        2. 7.4.12.2  Output Over-Voltage Protection (OVP)
        3. 7.4.12.3  Input Over Voltage Protection (IOVP)
        4. 7.4.12.4  Over-Temperature Protection (OTP) on FLT Pin
        5. 7.4.12.5  Over-Temperature Protection (OTP) on CS Pin
        6. 7.4.12.6  Programmable Over-Power Protection (OPP)
        7. 7.4.12.7  Peak Power Limit (PPL)
        8. 7.4.12.8  Output Short-Circuit Protection (SCP)
        9. 7.4.12.9  Over-Current Protection (OCP)
        10. 7.4.12.10 External Shutdown
        11. 7.4.12.11 Internal Thermal Shutdown
      13. 7.4.13 Pin Open/Short Protections
        1. 7.4.13.1 Protections on CS pin Fault
        2. 7.4.13.2 Protections on P13 pin Fault
        3. 7.4.13.3 Protections on RDM and RTZ pin Faults
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application Circuit
      1. 8.2.1 Design Requirements for a 60-W, 15-V ZVSF Bias Supply Application with a DC Input
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Input Bulk Capacitance and Minimum Bulk Voltage
        2. 8.2.2.2 Transformer Calculations
          1. 8.2.2.2.1 Primary-to-Secondary Turns Ratio (NPS)
          2. 8.2.2.2.2 Primary Magnetizing Inductance (LM)
          3. 8.2.2.2.3 Primary Winding Turns (NP)
          4. 8.2.2.2.4 Secondary Winding Turns (NS)
          5. 8.2.2.2.5 Auxiliary Winding Turns (NA)
          6. 8.2.2.2.6 Winding and Magnetic Core Materials
        3. 8.2.2.3 Calculation of ZVS Sensing Network
        4. 8.2.2.4 Calculation of BUR Pin Resistances
        5. 8.2.2.5 Calculation of Compensation Network
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1  General Considerations
      2. 10.1.2  RDM and RTZ Pins
      3. 10.1.3  SWS Pin
      4. 10.1.4  VS Pin
      5. 10.1.5  BUR Pin
      6. 10.1.6  FB Pin
      7. 10.1.7  CS Pin
      8. 10.1.8  AGND Pin
      9. 10.1.9  PGND Pin
      10. 10.1.10 Thermal Pad
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Receiving Notification of Documentation Updates
    2. 11.2 Support Resources
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information
8.2.2.2.3 Primary Winding Turns (NP)

The number of turns on the primary winding (NP) of the transformer is determined by two design considerations:

  1. The maximum flux density (BMAX) must be kept below the saturation limit (BSAT) of the chosen magnetic core under the highest peak magnetizing current (IM+(MAX)) condition, the cross-sectional area (AE) of the core, and highest core temperature. When IFB = 0 A, such as during VO soft-start or step-up load transient, the peak magnetizing current reaches IM+(MAX), since VCST = VCST(MAX) in those conditions. IM+(MAX) can be estimated based on the output power triggering an OPP fault (PO(OPP)) with VCST = VCST(OPP1) at VBULK(MIN).
    Equation 25. GUID-50CA4B75-4D7B-42CE-8928-C9A84F485F1C-low.gif
    Equation 26. GUID-78E8A2FD-4939-4FC5-AD26-0D3D4B8B7DD2-low.gif
  2. The AC flux density (ΔB) affects the core loss of the transformer. For a transition-mode ZVS flyback, the core loss is usually highest at high line, since the switching frequency is highest, duty cycle is smallest, and peak-to-peak magnetizing current swing is greatest for a given load condition. The following equation is the ΔB calculation including the contribution of negative magnetizing current (IM-), used to put into the Steinmetz equation for more accurate core loss estimation. For VBULK ≥ NPS(VO+VF), IM- is calculated with VBULK divided by the characteristic impedance of LM and the lumped time-related switch-node capacitance (CSW). IM- is always a negative value. The expression of fSW is derived based on the triangular approximation of the magnetizing current, which also considers the effect of IM- over wide DC or AC input line conditions.
    Equation 27. GUID-A4A0411D-C67D-4F73-ABBF-8CAE0B8CE330-low.gif
    Equation 28. GUID-CC8A2C3F-703F-46F5-B0BE-D0373AD79EDD-low.gif
    Equation 29. GUID-CDD8369E-471B-438B-A4ED-AA6624593963-low.gif
    Equation 30. GUID-7007B10F-B567-468C-AC1D-30CCA015B85F-low.gif
    Equation 31. GUID-AC5D9FFD-5133-4A72-8F28-DF62C2C8E496-low.gif
    Equation 32. GUID-EDB889DB-DA5A-4420-AE97-E0C9E638F958-low.gif

For the ΔB calculation, remember that IM- is a negative value and that ΔB is a peak-to-peak flux swing. Core loss is based on ½ of ΔB.