SLUSD12A October   2017  – February 2018 UCC28780

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Schematic
      2.      45-W, 20-V GaN-ACF Adapter Efficiency
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin 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 of SOIC
    5. 6.5 Thermal Information of WQFN
    6. 6.6 Electrical Characteristics
    7. 6.7 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 VDD Pin (Device Bias Supply)
      4. 7.3.4 REF Pin (Internal 5-V Bias)
      5. 7.3.5 HVG and SWS Pins
      6. 7.3.6 RTZ Pin (Sets Delay for Transition Time to Zero)
      7. 7.3.7 RDM Pin (Sets Synthesized Demagnetization Time for ZVS Tuning)
      8. 7.3.8 RUN Pin (Driver Enable Pin)
      9. 7.3.9 SET Pin
    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  Control Law across Entire Load Range
      4. 7.4.4  Adaptive Amplitude Modulation (AAM)
      5. 7.4.5  Adaptive Burst Mode (ABM)
      6. 7.4.6  Low Power Mode (LPM)
      7. 7.4.7  Standby Power Mode (SBP)
      8. 7.4.8  Startup Sequence
      9. 7.4.9  Survival Mode of VDD
      10. 7.4.10 System Fault Protections
        1. 7.4.10.1 Brown-In and Brown-Out
        2. 7.4.10.2 Output Over-Voltage Protection
        3. 7.4.10.3 Over-Temperature Protection
        4. 7.4.10.4 Programmable Over-Power Protection
        5. 7.4.10.5 Peak Current Limit
        6. 7.4.10.6 Output Short-Circuit Protection
        7. 7.4.10.7 Over-Current Protection
        8. 7.4.10.8 Thermal Shutdown
      11. 7.4.11 Pin Open/Short Protections
        1. 7.4.11.1 Protections on CS pin Fault
        2. 7.4.11.2 Protections on HVG pin Fault
        3. 7.4.11.3 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
      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 Turns (NP)
          4. 8.2.2.2.4 Secondary Turns (NS)
          5. 8.2.2.2.5 Turns of Auxiliary Winding (NA)
          6. 8.2.2.2.6 Winding and Magnetic Core Materials
        3. 8.2.2.3 Clamp Capacitor Calculation
        4. 8.2.2.4 Bleed-Resistor Calculation
        5. 8.2.2.5 Output Filter Calculation
        6. 8.2.2.6 Calculation of ZVS Sensing Network
        7. 8.2.2.7 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 GND Pin
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Community Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

7.1 Overview

The UCC28780 is a transition-mode (TM) active clamp flyback (ACF) controller, equipped with advanced control schemes to enable significant size reduction of passive components for higher power density and higher average efficiency. The control law is optimized for Silicon (Si) and Gallium Nitride (GaN) power FETs in a half-bridge configuration and is capable of driving high-frequency AC/DC converters up to 1 MHz. The zero voltage switching (ZVS) control of the UCC28780 is capable of auto-tuning the on-time of a high-side clamp switch (QH) by using a unique lossless ZVS sensing network connected between the switch-node voltage (VSW) and SWS pin. The ACF controller is designed to adaptively achieve targeted full-ZVS or partial-ZVS conditions for the low-side main switch (QL) with minimum circulating energy over wide operating conditions. Auto-tuning eliminates the risk of losing ZVS due to component tolerance, input/output voltage changes, and temperature variations, since the QH on-time is corrected cycle-by-cycle.

Dead-times between PWML (controls QL) and PWMH (controls QH) are optimally adjusted to help minimize the circulating energy required for ZVS. Therefore, the overall system efficiency can be significantly improved and more consistent efficiency can be obtained in mass production of the soft-switching topology. The programming features of the RTZ, RDM, BUR, and SET pins provide rich flexibility to optimize the power stage efficiency across a range of output power and operating frequency levels.

The UCC28780 uses four different operating modes to maximize efficiency over wide load and line ranges. Adaptive amplitude modulation (AAM) adjusts the peak primary current at the higher load levels. Adaptive burst mode (ABM) modulates the pulse count of each burst packet in the medium to light load range. Low power mode (LPM) reduces the peak primary current of each two-pulse burst packet in the very light load range. Standby power (SBP) mode minimizes the loss during no load conditions.

The unique burst mode control of the UCC28780 maximizes the light load efficiency of the ACF power stage, while avoiding the concerns of conventional burst operation - such as output ripple and audible noise. The burst control provides an enable signal through the RUN pin to dynamically manage the static current of the half-bridge driver and also adaptively disables the on-time of QH. These functions can be used to manage the quiescent power consumed by the half-bridge driver, further improving the converter’s light-load efficiency and reducing its standby power.

Instead of using a conventional high-voltage resistor, the UCC28780 starts up the VDD supply voltage with an external high-voltage depletion-mode MOSFET between the SWS pin and the switch node. Fast startup is achieved with low standby power overhead. Moreover, the HVG pin controls the gate of the depletion-mode FET to also allow this MOSFET to be used in a lossless ZVS sensing. This arrangement avoids additional sensing devices.

The UCC28780 also integrates a robust set of protection features tailored to maximize the reliability. These features include internal soft start, brown in/out, output over-voltage, output over-power, system over-temperature, switch over-current, output short-circuit protection, and pin open/short.