TIDUBE1D January   2016  – August 2024

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1. 1.1 Key System Specifications
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Highlighted Products and Key Advantages
      1. 2.2.1 UCC28180 – PFC Controller
      2. 2.2.2 UCC27524 – Dual Low-Side Gate Driver
      3. 2.2.3 UCC28881 – 700-V Off-Line Converter
    3. 2.3 System Design Theory
      1. 2.3.1 Selecting Switching Frequency
      2. 2.3.2 Calculating Output Capacitance
      3. 2.3.3 Calculating PFC Choke Inductor
      4. 2.3.4 Selecting Switching Element
      5. 2.3.5 Boost Follower Control Circuit
      6. 2.3.6 Bias Power
      7. 2.3.7 On-Off Switch
      8. 2.3.8 Thermal Design
  9. 3Hardware, Testing Requirements, and Test Results
    1. 3.1 Required Hardware
      1. 3.1.1 Test Conditions
      2. 3.1.2 Recommended Equipment
      3. 3.1.3 Procedure
    2. 3.2 Test Results
      1. 3.2.1 Performance Data
        1. 3.2.1.1 Efficiency and iTHD
        2. 3.2.1.2 Standby Power and Output Voltage
      2. 3.2.2 Performance Curves
        1. 3.2.2.1 Efficiency Curve
        2. 3.2.2.2 Voltage Follower Performance
      3. 3.2.3 Functional Waveforms
        1. 3.2.3.1 Power On Sequence
        2. 3.2.3.2 Inrush Current Protection
        3. 3.2.3.3 Switching Node
        4. 3.2.3.4 Waveform Under 3.5kW, 230VAC
      4. 3.2.4 Thermal Measurements
  10. 4Design Files
    1. 4.1 Schematics
    2. 4.2 Bill of Materials
  11. 5Documentation Support
  12. 6Trademarks
  13. 7About the Author
  14. 8Revision History

2.3.1 Selecting Switching Frequency

The UCC28180 switching frequency is user programmable with a single resistor on the FREQ pin to GND.

This design uses a 45kHz switching frequency. Calculate the suitable resistor value to program the switching frequency using Equation 1.

Equation 1. TIDA-00779

where:

  • fTYP, RTYP, and RINT are constants internally fixed to the controller that are based on the UCC28180 control logic
  • fTYP = 65kHz
  • RTYP = 32.7kΩ
  • RINT = 1MΩ

Applying these constants in Equation 2 yields the appropriate resistor that must be placed between the FREQ and GND pins.

Equation 2. TIDA-00779

A typical value of 47kΩ for the FREQ resistor results in a switching frequency of 44kHz.