SLUSD60 October   2017 UCC256304

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and 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 High Voltage Start-Up
      3. 7.4.3 X-Capacitor Discharge
      4. 7.4.4 Soft-Start and Burst-Mode Threshold
      5. 7.4.5 System States and Faults State Machine
      6. 7.4.6 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  Custom Design With WEBENCH® Tools
        2. 8.2.2.2  LLC Power Stage Requirements
        3. 8.2.2.3  LLC Gain Range
        4. 8.2.2.4  Select Ln and Qe
        5. 8.2.2.5  Determine Equivalent Load Resistance
        6. 8.2.2.6  Determine Component Parameters for LLC Resonant Circuit
        7. 8.2.2.7  LLC Primary-Side Currents
        8. 8.2.2.8  LLC Secondary-Side Currents
        9. 8.2.2.9  LLC Transformer
        10. 8.2.2.10 LLC Resonant Inductor
        11. 8.2.2.11 LLC Resonant Capacitor
        12. 8.2.2.12 LLC Primary-Side MOSFETs
        13. 8.2.2.13 Design Considerations for Adaptive Dead-Time
        14. 8.2.2.14 LLC Rectifier Diodes
        15. 8.2.2.15 LLC Output Capacitors
        16. 8.2.2.16 HV Pin Series Resistors
        17. 8.2.2.17 BLK Pin Voltage Divider
        18. 8.2.2.18 BW Pin Voltage Divider
        19. 8.2.2.19 ISNS Pin Differentiator
        20. 8.2.2.20 VCR Pin Capacitor Divider
        21. 8.2.2.21 Burst Mode Programming
        22. 8.2.2.22 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

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

9 Power Supply Recommendations

9.1 VCC Pin Capacitor

The VCC capacitor should be sized based on the total start-up charge required by the system. The start-up charge will mostly be consumed by the gate driver circuit. Thus the total start-up charge can be estimated by the start-up switching frequency, MOSFET gate charge, and the soft-start time.

Assume the total start-up charge required by the system is shown in Equation 77

Equation 77. UCC256304 qu73_sluscu6.gif

During PFC and LLC startup phase, the maximum VCC voltage drop allowed is

Equation 78. UCC256304 qu74_sluscu6.gif

The minimum VCC capacitor needed:

Equation 79. UCC256304 qu75_sluscu6.gif

Choose 110-µF capacitor.

9.2 Boot Capacitor

During burst off period, power consumed by the high side gate driver from the HB pin must be drawn from CBOOT and will cause its voltage to decay. At the start of the next burst period there must be sufficient voltage remaining on CBOOT to power the high side gate driver until the conduction period of LO allows it to be replenished from CRVCC. The power consumed by the high side driver during this burst off period will therefore have a direct impact on the size and cost of capacitors that must be connected to CBOOT and RVCC.

Assume the system has a maximum burst off period of 10 ms.

Equation 80. UCC256304 qu76_sluscu6.gif

Assume the bootstrap diode has a forward voltage drop of 1 V:

Equation 81. UCC256304 qu77_sluscu6.gif

Assume the boot voltage to be always above 8 V to avoid UVLO fault. Then the maximum allowed voltage drop on boot capacitor is:

Equation 82. UCC256304 qu78_sluscu6.gif

Boot capacitor can then be sized:

Equation 83. UCC256304 qu79_sluscu6.gif
UCC256304 Cboot vs max burst off_sluscu6.gif Figure 62. Minimum Required Boot Capacitance vs. Maximum Burst Off Period

9.3 RVCC Pin Capacitor

RVCC capacitor needs to be at least 5 times of boot capacitor. In addition, sizing of the RVCC capacitor depends on the stability of RVCC LDO. If load is light on RVCC, smaller capacitors can be used. The larger the load, the larger the capacitor is needed. In a typical system, the RVCC LDO powers the PFC and LLC gate drivers. The plot below shows the worst case RVCC LDO phase margin versus RVCC capacitor for various load currents. RVCC capacitor should be sized based on the figure below.

UCC256304 RVCC cap_sluscu6.gif Figure 63. RVCC Pin Capacitor