SLUSDW0B May   2020  – May 2020 UCC28065

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Application
  4. 4 Revision History
  5. 5 Description (Continued)
  6. 6 Pin Configuration and Functions
    1.     Pin Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Principles of Operation
      2. 8.3.2  Natural Interleaving
      3. 8.3.3  On-Time Control, Maximum Frequency Limiting, Restart Timer and Input Voltage Feed-Forward compensation
      4. 8.3.4  Zero-Current Detection and Valley Switching
      5. 8.3.5  Phase Management and Light-Load Operation
      6. 8.3.6  Burst Mode Operation
      7. 8.3.7  External Disable
      8. 8.3.8  Improved Error Amplifier
      9. 8.3.9  Soft Start
      10. 8.3.10 Brownout Protection
      11. 8.3.11 Line Dropout Detection
      12. 8.3.12 VREF
      13. 8.3.13 VCC
      14. 8.3.14 System Level Protections
        1. 8.3.14.1 Failsafe OVP - Output Over-voltage Protection
        2. 8.3.14.2 Overcurrent Protection
        3. 8.3.14.3 Open-Loop Protection
        4. 8.3.14.4 VCC Undervoltage Lock-Out (UVLO) Protection
        5. 8.3.14.5 Phase-Fail Protection
        6. 8.3.14.6 CS - Open, TSET - Open and Short Protection
        7. 8.3.14.7 Thermal Shutdown Protection
        8. 8.3.14.8 Fault Logic Diagram
    4. 8.4 Device Functional Modes
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1  Inductor Selection
        2. 9.2.2.2  ZCD Resistor Selection RZA, RZB
        3. 9.2.2.3  HVSEN
        4. 9.2.2.4  Output Capacitor Selection
        5. 9.2.2.5  Selecting RS For Peak Current Limiting
        6. 9.2.2.6  Power Semiconductor Selection (Q1, Q2, D1, D2)
        7. 9.2.2.7  Brownout Protection
        8. 9.2.2.8  Converter Timing
        9. 9.2.2.9  Programming VOUT
        10. 9.2.2.10 Voltage Loop Compensation
      3. 9.2.3 Application Curves
        1. 9.2.3.1 Input Ripple Current Cancellation with Natural Interleaving
        2. 9.2.3.2 Brownout Protection
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Community Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information
    1. 13.1 Package Option Addendum
      1. 13.1.1 Packaging Information

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8.3.3 On-Time Control, Maximum Frequency Limiting, Restart Timer and Input Voltage Feed-Forward compensation

Gate-drive on-time varies proportionately with the error-amplifier output voltage (VCOMP) and inversely proportional to the squared value of the peak of the rectified input voltage sensed through VINAC pin as stated by Equation 3. In Equation 3 it is shown that the on-time is inversely proportionally to the value of resistor RTSET connected between pin TSET and pin AGND. In order to calculate on-time, Equation 4 can be used. Parameter KT is function of the rectified peak input voltage sensed by pin VINAC as reported in graph of Figure 16. In this graph three curves are reported for three different values of RTSET. Two values of parameter KT are reported in Electrical Characteristics the electrical specs table for two values of VINAC: KTL and KTH corresponding at the VINAC = 1.6V and VINAC = 5V and RTSET = 133kΩ. Because voltage on VINAC is proportional to the line rectified voltage, for tON calculation purposes we refer to the peak value of this voltage that is obtained through an internal peak detect. KT is inversely proportional to the squared value of VINAC peak value so it is the tON time realizing the so called voltage feed-forward compensation. The Voltage Feed-forward function modifies the MOSFET on time according to line voltage so, ideally output power delivered does not change if line voltage changes. When operating in single phase mode KT is called KTS and its value is doubled.

Equation 3. UCC28065 eq3.gif

The COMP pin voltage value is clamped at 4.95 V, so the maximum on time can be calculated by Equation 4.

Equation 4. UCC28065 eq4.gif

Figure 16 shows the values of KT versus the peak voltage value on VINAC pin.

UCC28065 D0123471.gifFigure 16. KT vs Peak Voltage

The maximum switching frequency of each phase is limited by minimum-period timers. If the inductor current decays to zero before the minimum-period timer elapses, the next turn on will be delayed, resulting in discontinuous phase current. As illustrated in Figure 17, when the ZCD signal arrives before the minimum period expires, the ZCD signal is ignored and the controller waits for the next ZCD signal after the minimum period expires to turn on the switch. The minimum switching period, tMIN, is inversely proportional to the time-setting resistor RTSET (the resistor from the TSET pin to ground). The typical tMIN as a function of TSET pin resistor value is shown in Figure 1. The UCC28065 device doubles the clamping frequency compared with UCC28064A. For more detailed comparison between UCC28065 and UCC28064A, refer to the application note "Convert UCC28064A EVM to Higher Switching Frequency Using UCC28065".

UCC28065 FreClamp.gifFigure 17. UCC28065 Frequency Clamp

A restart timer ensures starting under all circumstances by restarting both phases if the ZCD input of either phase has not transitioned from high-to-low within approximately 210 µs.