SLUSDB2B August   2018  – October 2024 UCC28950 , UCC28951

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Timing Requirements
    7. 5.7 Dissipation Ratings
    8. 5.8 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1  Start-Up Protection Logic
      2. 6.3.2  Voltage Reference (VREF)
      3. 6.3.3  Error Amplifier (EA+, EA–, COMP)
      4. 6.3.4  Soft-Start and Enable (SS/EN)
      5. 6.3.5  Light-Load Power Saving Features
      6. 6.3.6  Adaptive Delay, (Delay Between OUTA and OUTB, OUTC and OUTD (DELAB, DELCD, ADEL))
      7. 6.3.7  Adaptive Delay (Delay Between OUTA and OUTF, OUTB and OUTE (DELEF, ADELEF)
      8. 6.3.8  Minimum Pulse (TMIN)
      9. 6.3.9  Burst Mode
      10. 6.3.10 Switching Frequency Setting
      11. 6.3.11 Slope Compensation (RSUM)
      12. 6.3.12 Dynamic SR ON/OFF Control (DCM Mode)
      13. 6.3.13 Current Sensing (CS)
      14. 6.3.14 Cycle-by-Cycle Current Limit Current Protection and Hiccup Mode
      15. 6.3.15 Synchronization (SYNC)
      16. 6.3.16 Outputs (OUTA, OUTB, OUTC, OUTD, OUTE, OUTF)
      17. 6.3.17 Supply Voltage (VDD)
      18. 6.3.18 Ground (GND)
    4. 6.4 Device Functional Modes
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
        1. 7.2.2.1  Power Loss Budget
        2. 7.2.2.2  Preliminary Transformer Calculations (T1)
        3. 7.2.2.3  QA, QB, QC, QD FET Selection
        4. 7.2.2.4  Selecting LS
        5. 7.2.2.5  Selecting Diodes DB and DC
        6. 7.2.2.6  Output Inductor Selection (LOUT)
        7. 7.2.2.7  Output Capacitance (COUT)
        8. 7.2.2.8  Select FETs QE and QF
        9. 7.2.2.9  Input Capacitance (CIN)
        10. 7.2.2.10 Current Sense Network (CT, RCS, R7, DA)
          1. 7.2.2.10.1 Voltage Loop Compensation Recommendation
      3. 7.2.3 Application Curves
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Development Support
    2. 8.2 Documentation Support
      1. 8.2.1 Related Documentation
    3. 8.3 Receiving Notification of Documentation Updates
    4. 8.4 Community Resources
    5. 8.5 Trademarks
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

7.2.3 Application Curves

Switch node QBd is valley switching and node QDd has achieved ZVS. Please refer to Figure 7-13 and Figure 7-14. It is not uncommon for switch node QDd to obtain ZVS before QBd. This is because during the QDd switch node voltage transition, the reflected output current provides immediate energy for the LC tank at the switch node. Where at the QBd switch node transition the primary has been shorted out by the high-side or low-side FETs in the H bridge. This transition is dependent on the energy stored in LS and LLK to provide energy for the LC tank at switch node QBd making it take longer to achieve ZVS.

UCC28950 UCC28951 Full-Bridge Gate Drives and Primary Switch Nodes (QBd and QDd)
VIN = 390VIOUT = 5A
Figure 7-11 Full-Bridge Gate Drives and Primary Switch Nodes (QBd and QDd)
UCC28950 UCC28951 Full-Bridge Gate Drives and Switch Nodes (QBg QBd)
VIN = 390VIOUT = 10A
Figure 7-13 Full-Bridge Gate Drives and Switch Nodes (QBg QBd)
UCC28950 UCC28951 Full-Bridge Gate Drives and Primary Switch Nodes (QDg QDd)
VIN = 390VIOUT = 5A
Figure 7-12 Full-Bridge Gate Drives and Primary Switch Nodes (QDg QDd)
UCC28950 UCC28951 Full-Bridge Gate Drives and Switch Nodes (QDg QDd)
VIN = 390VIOUT = 10A
Figure 7-14 Full-Bridge Gate Drives and Switch Nodes (QDg QDd)
UCC28950 UCC28951 Full-Bridge Gate Drives and Switch Nodes (QBg QBd)
VIN = 390VIOUT = 25A
Figure 7-15 Full-Bridge Gate Drives and Switch Nodes (QBg QBd)
UCC28950 UCC28951 Full-Bridge Gate Drives and Switch Nodes (QDg QDd)
VIN = 390VIOUT = 25A
Figure 7-16 Full-Bridge Gate Drives and Switch Nodes (QDg QDd)

When the converter is running at 25A, both switch nodes are operating into zero voltage switching (ZVS). It is also worth mentioning that there is no evidence of the gate miller plateau during gate driver switching. This is because the voltage across the drains and sources of FETs QA through QD transitioned earlier.

UCC28950 UCC28951 Full-Bridge Gate Drives and Switch Nodes (QBg QBd)
VIN = 390VIOUT = 50A
Figure 7-17 Full-Bridge Gate Drives and Switch Nodes (QBg QBd)
UCC28950 UCC28951 Full-Bridge Gate Drives and Switch Nodes (QDg QDd)
VIN = 390VIOUT = 50A
ZVS maintained from 50% to 100% output power
Figure 7-18 Full-Bridge Gate Drives and Switch Nodes (QDg QDd)