SLUSFF2C September   2023  – December 2025 UCG28824 , UCG28826 , UCG28828

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison
  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 Typical Characteristics
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Detailed Pin Descriptions
      1. 7.3.1  HV - High Voltage Input
      2. 7.3.2  SW - Switch Node
      3. 7.3.3  GND – Ground Return
      4. 7.3.4  FLT - External Overtemperature Fault
      5. 7.3.5  FB ­­– Feedback
      6. 7.3.6  TR - Turns Ratio
      7. 7.3.7  IPK - Peak Current and Dithering
      8. 7.3.8  FCL - Frequency Clamp and Fault Response
      9. 7.3.9  CDX - CCM, Drive Strength, and X-cap Discharge
      10. 7.3.10 VCC - Input Bias
    4. 7.4 Feature Description
      1. 7.4.1  Self Bias and Auxless Sensing
      2. 7.4.2  Control Law
        1. 7.4.2.1 Valley Switching
        2. 7.4.2.2 Frequency Foldback
        3. 7.4.2.3 Burst Mode
        4. 7.4.2.4 Continuous Conduction Mode (CCM)
      3. 7.4.3  GaN HEMT Switching Capability
      4. 7.4.4  Soft Start
      5. 7.4.5  Frequency Clamp
      6. 7.4.6  Frequency Dithering
      7. 7.4.7  Slew Rate Control
      8. 7.4.8  Transient Peak Power Capability
      9. 7.4.9  X-Cap Discharge
      10. 7.4.10 Fault Protections
        1. 7.4.10.1 Brownout Protection
        2. 7.4.10.2 Short-Circuit Protection
        3. 7.4.10.3 Output Overvoltage Protection
        4. 7.4.10.4 Overpower Protection (OPP, LPS)
        5. 7.4.10.5 Overtemperature Protection
        6. 7.4.10.6 Open FB Protection
        7. 7.4.10.7 Error Codes for Protections
  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 Input Bulk Capacitor
        2. 8.2.2.2 Transformer Primary Inductance and Turns Ratio
        3. 8.2.2.3 Output Capacitor
        4. 8.2.2.4 Selection Resistors
      3. 8.2.3 Application Curves
    3. 8.3 Power Supply Recommendations
    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

7.3.6 TR - Turns Ratio

Set the transformer turns ratio information with a resistor from this pin to GND as per values in Table 7-1 or Table 7-2. The turns ratio information is used for output voltage sensing. The resistor must be 1% accurate.

Table 7-1 Turns Ratio Setting Resistor Values
TR Pin Resistor (kΩ) Turns Ratio VOUT OVP Threshold (V, Reflected to Primary)
0 7.875 196.9
5.23 6 150
6.34 6.125 153.1
7.68 6.25 156.2
9.31 6.375 159.4
11.3 6.5 162.5
13.7 6.625 165.6
16.9 6.75 168.7
20.5 6.875 171.9
25.5 7 175
31.6 7.125 178.1
39.2 7.25 181.2
51.1 7.375 184.4
66.5 7.5 187.5
84.5 7.625 190.6
113 7.75 193.7
174 7.875 196.9
Table 7-2 Turns Ratio Setting Resistor Values for UCG288826-4
TR Pin Resistor (kΩ) Turns Ratio VOUT OVP Threshold (V, Reflected to Primary)
0 7.875 126
5.23 6 96
6.34 6.125 98
7.68 6.25 100
9.31 6.375 102
11.3 6.5 104
13.7 6.625 106
16.9 6.75 108
20.5 6.875 110
25.5 7 112
31.6 7.125 114
39.2 7.25 116
51.1 7.375 118
66.5 7.5 120
84.5 7.625 122
113 7.75 124
174 7.875 126

The TR pin sets up the transformer turns ratio assuming the design is used for USB-PD application. When used for other applications, the TR pin setting follows different principle.In reality, the TR pin is used to set the output OVP level. The UCG2882x uses the auxless sensing technology and can't directly tell the output voltage level. The TR pin sets the output OVP level based on the output voltage reflected to the primary side. Bascically, in those applications, choose the TR pin resistor value based on the VOUT OVP Threshold (V, Reflected to Primary) colum in Table 7-1 and Table 7-2. Refer to the application note for more details.