SLUSD49A September   2017  – January 2019 UCC256303


  1. Features
  2. Applications
  3. Description
    1.     Simplified Schematic
  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
    5. 6.5 Electrical Characteristics
    6. 6.6 Switching Characteristics
    7. 6.7 Typical Characteristics
  7. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Hybrid Hysteretic Control
      2. 7.3.2  Regulated 12-V Supply
      3. 7.3.3  Feedback Chain
      4. 7.3.4  Optocoupler Feedback Signal Input and Bias
      5. 7.3.5  System External Shut Down
      6. 7.3.6  Pick Lower Block and Soft Start Multiplexer
      7. 7.3.7  Pick Higher Block and Burst Mode Multiplexer
      8. 7.3.8  VCR Comparators
      9. 7.3.9  Resonant Capacitor Voltage Sensing
      10. 7.3.10 Resonant Current Sensing
      11. 7.3.11 Bulk Voltage Sensing
      12. 7.3.12 Output Voltage Sensing
      13. 7.3.13 High Voltage Gate Driver
      14. 7.3.14 Protections
        1. ZCS Region Prevention
        2. Over Current Protection (OCP)
        3. Over Output Voltage Protection (VOUTOVP)
        4. Over Input Voltage Protection (VINOVP)
        5. Under Input Voltage Protection (VINUVP)
        6. Boot UVLO
        7. RVCC UVLO
        8. Over Temperature Protection (OTP)
    4. 7.4 Device Functional Modes
      1. 7.4.1 Burst Mode Control
      2. 7.4.2 Soft-Start and Burst-Mode Threshold
      3. 7.4.3 System States and Faults State Machine
      4. 7.4.4 Waveform Generator State Machine
  8. Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1.  LLC Power Stage Requirements
        2.  LLC Gain Range
        3.  Select Ln and Qe
        4.  Determine Equivalent Load Resistance
        5.  Determine Component Parameters for LLC Resonant Circuit
        6.  LLC Primary-Side Currents
        7.  LLC Secondary-Side Currents
        8.  LLC Transformer
        9.  LLC Resonant Inductor
        10. LLC Resonant Capacitor
        11. LLC Primary-Side MOSFETs
        12. Design Considerations for Adaptive Dead-Time
        13. LLC Rectifier Diodes
        14. LLC Output Capacitors
        15. BLK Pin Voltage Divider
        16. BW Pin Voltage Divider
        17. ISNS Pin Differentiator
        18. VCR Pin Capacitor Divider
        19. Burst Mode Programming
        20. Soft-Start Capacitor
      3. 8.2.3 Application Curves
  9. Power Supply Recommendations
    1. 9.1 VCC Pin Capacitor
    2. 9.2 Boot Capacitor
    3. 9.3 RVCC Pin Capacitor
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Development Support
        1. Custom Design With WEBENCH® Tools
    2. 11.2 Documentation Support (if applicable)
      1. 11.2.1 Related Documentation
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 Community Resources
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • DDB|14
Thermal pad, mechanical data (Package|Pins)
Orderable Information

ZCS Region Prevention

Capacitive region is an LLC operation region in which the voltage gain increases when the switching frequency increases. It is also called ZCS region. Capacitive mode operation should be avoided for two reasons:

  • The feedback loop becomes positive feedback in capacitive region
  • The MOSFET may be damaged because of body diode reverse recovery

To make sure that capacitive region operation does not happen, we need to first rely on the slew done signal. If there is a slew done signal detected, it suggests that the opposite body diode must not be conducting and to turn on the next FET. If there is no slew detected, IPolarity signal is used. The next gate will be turned on at the next IPolarity flip event. The IPolarity flip indicates that the capacitive operation cycle has already passed. The resonant current reverses the direction and begins to discharge the switch node. When the capacitive operation cycle has passed, the system enters a high frequency oscillation stage, where the oscillation frequency is determined by the parasitic elements in the circuit. In this stage, the body diode is no longer conducting and it is allowed to turn on the next gate.

However, in the high frequency oscillation stage, the resonant current may be so small that the IPolarity detection is missed. In this case, the next gate will be turned on by maximum dead time timer expiration.

In addition to preventing the next gate from turning on when the opposite body diode is conducting, the switching frequency is forced to ramp up until there is a cycle with no capacitive region operation detected

The capacitive region detection is done by checking the resonant current polarity at HSON or LSON falling edge. If the resonant current is positive at LSON falling edge, or negative at HSON falling edge, the ZCS signal in the waveform generator is turned high. The ZCS signal keeps high until there is a half cycle without capacitive region operation happens.

The force ramping up of the switching frequency is done by pull the SS pin down by a resistor to ground. Details will be discussed in SS pin section.

Below is the flow chart of capacitive region prevention algorithm:

UCC256303 sluscu6_gate_driver_block_diagram2.gifFigure 34. Gate Driver Block Diagram
UCC256303 fig50_sluscu6.gifFigure 35. Timing Diagram of a ZCS Event