SLVSIL5A May   2025  – September 2025 UCC25661-Q1

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison Table
  6. 5 Pin Configuration and Functions
  7. 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
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Input Power Proportional Control
        1. 7.3.1.1 Voltage Feedforward
      2. 7.3.2 VCR Synthesizer
        1. 7.3.2.1 TSET Programming
      3. 7.3.3 Feedback Chain (Control Input)
      4. 7.3.4 Adaptive Dead Time
      5. 7.3.5 Input Voltage Sensing
        1. 7.3.5.1 Brownin and Brownout Thresholds and Options
        2. 7.3.5.2 Output OVP and External OTP
      6. 7.3.6 Resonant Tank Current Sensing
    4. 7.4 Protections
      1. 7.4.1 Zero Current Switching (ZCS) Protection
      2. 7.4.2 Minimum Current Turn-off During Soft Start
      3. 7.4.3 Cycle-by-Cycle Current Limit and Short Circuit Protection
      4. 7.4.4 Overload Protection (OLP)
      5. 7.4.5 VCC OVP Protection
    5. 7.5 Device Functional Modes
      1. 7.5.1 Startup
        1. 7.5.1.1 With HV Startup
        2. 7.5.1.2 Without HV Startup
      2. 7.5.2 Soft Start Ramp
        1. 7.5.2.1 Startup Transition to Regulation
      3. 7.5.3 Light Load Management
        1. 7.5.3.1 Operating Modes (Burst Pattern)
        2. 7.5.3.2 Mode Transition Management
        3. 7.5.3.3 Burst Mode Thresholds Programming
        4. 7.5.3.4 PFC On/Off
  9. 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 HV Pin Series Resistors
        16. 8.2.2.16 BLK Pin Voltage Divider
        17. 8.2.2.17 ISNS Pin Differentiator
        18. 8.2.2.18 TSET Pin
        19. 8.2.2.19 OVP/OTP Pin
        20. 8.2.2.20 Burst Mode Programming
        21. 8.2.2.21 Application Curves
    3. 8.3 Power Supply Recommendations
      1. 8.3.1 VCCP Pin Capacitor
      2. 8.3.2 Boot Capacitor
      3. 8.3.3 V5P Pin Capacitor
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Receiving Notification of Documentation Updates
    2. 9.2 Support Resources
    3. 9.3 Trademarks
    4. 9.4 Electrostatic Discharge Caution
    5. 9.5 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

8.2.2.5 Determine Component Parameters for LLC Resonant Circuit

Before finalizing the resonant tank component parameters, select a nominal switching frequency (resonant frequency). In the UCC25661EVM-128 180W design, 100kHz is the resonant frequency. Higher resonant frequency shrink passive components. Some designers limit the maximum resonant frequency, avoiding the AM band to meet CISPR 25 standards for EMC.

Equation 19. f 0 = 100 k H z

Calculate the resonant tank parameters using Equation 20, Equation 21, and Equation 22.

Equation 20. C R = 1 2 π × Q E × f 0 × R E = 1 2 π × 0.3 × 100 k H z × 176.5 Ω = 30.0 n F
Equation 21. L R = 1 2 π × f 0 2 C R = 1 2 π × 100 k H z 2 × 30.0 n F = 84.4 μ H
Equation 22. L M = L N × L R = 6 × 84.4 μ H = 506.4 μ H

After selecting the preliminary parameters, find the closest actual component value that is available, and reassess the gain curve. Verify the circuit operation by running a time domain simulation in SIMPLIS or another modeling tool. Running simulations allows testing many unique combinations and iterations of resonant tank parameters without purchasing components and waiting for delivery.

The following resonant tank parameters are:

Equation 23. C R = 30 n F
Equation 24. L R = 85 μH
Equation 25. L M = 510 μ H

Based on the final resonant tank parameters, confirm the desired resonant frequency is calculated from the following equation:

Equation 26. f 0 = 1 2 π L R C R = 1 2 π 30 n F × 85 μ H = 99.7 k H z

Based on the new LLC gain curve, the normalized switching frequency at maximum and minimum gain are given by:

Equation 27. f N M g m a x = 0.7
Equation 28. f N M g m i n = 1.0

The maximum and minimum switching frequencies are a product of the normalized switching frequency and the corresponding gain:

Equation 29. f S W M g m a x = 69.8 k H z
Equation 30. f S W M g m i n = 99.7 k H z