SLUSD49A September   2017  – January 2019 UCC256303

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Simplified Schematic
  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
    5. 6.5 Electrical Characteristics
    6. 6.6 Switching Characteristics
    7. 6.7 Typical Characteristics
  7. 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. 7.3.14.1 ZCS Region Prevention
        2. 7.3.14.2 Over Current Protection (OCP)
        3. 7.3.14.3 Over Output Voltage Protection (VOUTOVP)
        4. 7.3.14.4 Over Input Voltage Protection (VINOVP)
        5. 7.3.14.5 Under Input Voltage Protection (VINUVP)
        6. 7.3.14.6 Boot UVLO
        7. 7.3.14.7 RVCC UVLO
        8. 7.3.14.8 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. 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. 8.2.2.1  LLC Power Stage Requirements
        2. 8.2.2.2  LLC Gain Range
        3. 8.2.2.3  Select Ln and Qe
        4. 8.2.2.4  Determine Equivalent Load Resistance
        5. 8.2.2.5  Determine Component Parameters for LLC Resonant Circuit
        6. 8.2.2.6  LLC Primary-Side Currents
        7. 8.2.2.7  LLC Secondary-Side Currents
        8. 8.2.2.8  LLC Transformer
        9. 8.2.2.9  LLC Resonant Inductor
        10. 8.2.2.10 LLC Resonant Capacitor
        11. 8.2.2.11 LLC Primary-Side MOSFETs
        12. 8.2.2.12 Design Considerations for Adaptive Dead-Time
        13. 8.2.2.13 LLC Rectifier Diodes
        14. 8.2.2.14 LLC Output Capacitors
        15. 8.2.2.15 BLK Pin Voltage Divider
        16. 8.2.2.16 BW Pin Voltage Divider
        17. 8.2.2.17 ISNS Pin Differentiator
        18. 8.2.2.18 VCR Pin Capacitor Divider
        19. 8.2.2.19 Burst Mode Programming
        20. 8.2.2.20 Soft-Start Capacitor
      3. 8.2.3 Application Curves
  9. 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. 11.1.1.1 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

7.3.9 Resonant Capacitor Voltage Sensing

The resonant capacitor voltage sense pin senses the resonant capacitor voltage through a capacitor divider. Inside the device, two well matched, controlled current sources are connected to VCR pin to generate the frequency compensation ramp. The on/off control signals in of the two current sources come from the waveform generator block.

During waveform generator IDLE state or before startup, short VCR node to Vcm. This action will help reduce the startup peak current, and help VCR voltage to settle down quickly during burst mode.

UCC256303 fig40_sluscu6.gifFigure 26. VCR Block Diagram

The ramp current on/off sequence is shown in Figure 27. The ramp current is on all the time. It changes direction at the falling edge of high side on or low side on signal.

UCC256303 fig41_sluscu6.gifFigure 27. VCR Compensation Ramp Current On/Off

On VCR pin, a capacitor divider is used to mix the resonant capacitor waveform and the compensation ramp waveform. Adjusting the size of the external capacitors can change the contribution of charge control and direct frequency control. Assume the divided down version of the resonant capacitor voltage by the capacitor divider is Vdiv, the compensation ramp current resulted voltage on VCR pin is Vramp. If Vdiv is much larger than Vramp, the control method is similar to charge control, in which the control effort is proportional to the input charge of one switching cycle. If Vramp is much larger than Vdiv, the control method is similar to direct frequency control, in which the control effort is proportional to the switching frequency. The most optimal transient response can be achieved by adjusting the ratio between Vdiv and Vramp.