SLUSD12A October   2017  – February 2018 UCC28780


  1. Features
  2. Applications
  3. Description
    1.     Device Images
      1.      Simplified Schematic
      2.      45-W, 20-V GaN-ACF Adapter Efficiency
  4. Revision History
  5. Pin Configuration and Functions
    1.     Pin Functions
  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. 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. Brown-In and Brown-Out
        2. Output Over-Voltage Protection
        3. Over-Temperature Protection
        4. Programmable Over-Power Protection
        5. Peak Current Limit
        6. Output Short-Circuit Protection
        7. Over-Current Protection
        8. Thermal Shutdown
      11. 7.4.11 Pin Open/Short Protections
        1. Protections on CS pin Fault
        2. Protections on HVG pin Fault
        3. Protections on RDM and RTZ pin Faults
  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. Input Bulk Capacitance and Minimum Bulk Voltage
        2. Transformer Calculations
          1. Primary-to-Secondary Turns Ratio (NPS)
          2. Primary Magnetizing Inductance (LM)
          3. Primary Turns (NP)
          4. Secondary Turns (NS)
          5. Turns of Auxiliary Winding (NA)
          6. Winding and Magnetic Core Materials
        3. Clamp Capacitor Calculation
        4. Bleed-Resistor Calculation
        5. Output Filter Calculation
        6. Calculation of ZVS Sensing Network
        7. Calculation of Compensation Network
      3. 8.2.3 Application Curves
  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

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • D|16
  • RTE|16
Thermal pad, mechanical data (Package|Pins)
Orderable Information

RTZ Pin (Sets Delay for Transition Time to Zero)

The dead-time between PWMH falling edge and PWML rising edge (tZ) serves as the wait time for VSW transition from its high level down to the target ZVS point. Since the optimal tZ varies with VBULK, the internal dead-time optimizer automatically extends tZ as VBULK is less than the highest voltage of the input bulk capacitor (VBULK(MAX)). The circulating energy for ZVS can be further reduced, obtaining higher efficiency at low line versus a fixed dead-time over a wide line voltage range. A resistor on RTZ pin (RRTZ) programs the minimum tZ (tZ(MIN)) at VBULK(MAX), which is the sum of the propagation delay of the high-side driver (tD(DR)) and the minimum resonant transition time of VSW falling edge (tLC(MIN)).

Equation 8. UCC28780 Equ-RRTZ-1.gif

where KTZ is equal to 11.2×1011 (unit: F-1) for VSET = 0 V, and 5.6×1011(unit: F-1) for VSET = 5 V. As illustrated in Figure 18, after PWMH turns off QH after tD(DR) delay, the negative magnetizing current (iM-) becomes an initial condition of the resonant tank formed by magnetizing inductance (LM) and the switch-node capacitance (CSW). CSW is the total capacitive loading on the switch-node, including all junction capacitance (COSS) of switching devices, stray capacitance of the boot-strap diode, intra-winding capacitance of the transformer, the snubber capacitor, and parasitic capacitance of the PCB traces between switch-node and ground. Unlike a conventional valley-switching flyback converter, the resonance of an active clamp flyback converter at high line does not begin at the peak of the sinusoidal trajectory. The transition time of VSW takes less than half of the resonance period. The following tLC(MIN) expression quantifies the transition time for RRTZ calculation, where an arccosine term represents the initial angle at the resonance beginning. The value of π minus the arccosine term at VBULK(MAX) of 375 V, VO of 20 V, and NPS of 5 is around 0.585π, which is close to one quarter of the resonance period.

Equation 9. UCC28780 Equ-TLC.gif
UCC28780 VSW-transition.gifFigure 18. RTZ Setting for the Falling-edge Transition of VSW