SLUSBE8B May   2013  – September 2015 UCC28720


  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Pin Configuration and Functions
  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
  7. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Detailed Pin Description
    4. 7.4 Device Functional Modes
      1. 7.4.1 Primary-Side Voltage Regulation
      2. 7.4.2 Primary-Side Current Regulation
      3. 7.4.3 Valley Switching
      4. 7.4.4 Start-Up Operation
      5. 7.4.5 Fault Protection
  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. Stand-by Power Estimate
        2. Input Bulk Capacitance and Minimum Bulk Voltage
        3. Transformer Turns Ratio, Inductance, Primary-Peak Current
        4. Transformer Parameter Verification
        5. Output Capacitance
        6. VDD Capacitance, CDD
        7. VS Resistor Divider, Line Compensation, and Cable Compensation
      3. 8.2.3 Application Curves
  9. Power Supply Recommendations
  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 Device Nomenclature
        1. Definition of Terms
          1.  Capacitance Terms in Farads
          2.  Duty Cycle Terms
          3.  Frequency Terms in Hertz
          4.  Current Terms in Amperes
          5.  Current and Voltage Scaling Terms
          6.  Transformer Terms
          7.  Power Terms in Watts
          8.  Resistance Terms in Ω
          9.  Timing Terms in Seconds
          10. Voltage Terms in Volts
          11. AC Voltage Terms in VRMS
          12. Efficiency Terms
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Community Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information



11 Device and Documentation Support

11.1 Device Support

11.1.1 Device Nomenclature Definition of Terms Capacitance Terms in Farads

  • CBULK: total input capacitance of CB1 and CB2.
  • CDD: minimum required capacitance on the VDD pin.
  • COUT: minimum output capacitance required. Duty Cycle Terms

  • DMAGCC: secondary diode conduction duty cycle in CC, 0.425.
  • DMAX: transistor on-time duty cycle. Frequency Terms in Hertz

  • fLINE: minimum line frequency.
  • fMAX: target full-load maximum switching frequency of the converter.
  • fMIN: minimum switching frequency of the converter, add 15% margin over the fSW(min) limit of the device.
  • fSW(min): minimum switching frequency (see Electrical Characteristics). Current Terms in Amperes

  • IOCC: converter output constant-current target.
  • IPP(max): maximum transformer primary current.
  • ISTART: start-up bias supply current (see Electrical Characteristics).
  • ITRAN : required positive load-step current.
  • IVSL(run): VS pin run current (see Electrical Characteristics). Current and Voltage Scaling Terms Transformer Terms

  • LP: transformer primary inductance.
  • NAS: transformer auxiliary-to-secondary turns ratio.
  • NPA: transformer primary-to-auxiliary turns ratio.
  • NPS: transformer primary-to-secondary turns ratio. Power Terms in Watts

  • PIN: converter maximum input power.
  • POUT: full-load output power of the converter.
  • PSB: total stand-by power.
  • PSB_CONV: PSB minus start-up resistor and snubber losses. Resistance Terms in Ω

  • RCS: primary current programming resistance.
  • RESR: total ESR of the output capacitor(s).
  • RPL: preload resistance on the output of the converter.
  • RS1: high-side VS pin resistance.
  • RS2: low-side VS pin resistance. Timing Terms in Seconds

  • tD: current-sense delay including transistor turn-off delay; add 50 ns to transistor delay.
  • tDMAG(min): minimum secondary rectifier conduction time.
  • tON(min): minimum transistor on time.
  • tR: resonant frequency during the DCM (discontinuous conduction mode) time. Voltage Terms in Volts

  • VBLK: highest bulk capacitor voltage for stand-by power measurement.
  • VBULK(min): minimum voltage on CB1 and CB2 at full power.
  • VOCBC: target cable compensation voltage at the output terminals.
  • VCBC(max): maximum voltage at the CBC pin at the maximum converter output current (see Electrical Characteristics).
  • VCCR: constant-current regulating voltage (see Electrical Characteristics).
  • VCST(max): CS pin maximum current-sense threshold (see Electrical Characteristics).
  • VCST(min): CS pin minimum current-sense threshold (see Electrical Characteristics).
  • VDD(off): UVLO turn-off voltage (see Electrical Characteristics).
  • VDD(on): UVLO turn-on voltage (see Electrical Characteristics).
  • V: output voltage drop allowed during the load-step transient.
  • VCPK: peak transistor collector to emitter voltage at high line.
  • VF: secondary rectifier forward voltage drop at near-zero current.
  • VFA: auxiliary rectifier forward voltage drop.
  • VLK: estimated leakage inductance energy reset voltage.
  • VOCV: regulated output voltage of the converter.
  • VOCC: target lowest converter output voltage in constant-current regulation.
  • VREV: peak reverse voltage on the secondary rectifier.
  • VRIPPLE: output peak-to-peak ripple voltage at full-load.
  • VVSR: CV regulating level at the VS input (see Electrical Characteristics). AC Voltage Terms in VRMS

  • VIN(max): maximum input voltage to the converter.
  • VIN(min): minimum input voltage to the converter.
  • VIN(run): converter input start-up (run) voltage. Efficiency Terms

  • ηSB: estimated efficiency of the converter at no-load condition, not including start-up resistance or bias losses. For a 5-V USB charger application, 60% to 65% is a good initial estimate.
  • η: converter overall efficiency.
  • ηXFMR: transformer primary-to-secondary power transfer efficiency.

11.2 Documentation Support

11.2.1 Related Documentation

See the following: Using the UCC28720EVM-212, Evaluation Module, SLUUA92.

11.3 Community Resources

The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of Use.

    TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration among engineers. At, you can ask questions, share knowledge, explore ideas and help solve problems with fellow engineers.
    Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and contact information for technical support.

11.4 Trademarks

E2E is a trademark of Texas Instruments.

All other trademarks are the property of their respective owners.

11.5 Electrostatic Discharge Caution


These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates.

11.6 Glossary

SLYZ022TI Glossary.

This glossary lists and explains terms, acronyms, and definitions.