SLUSBD8E February   2013  – December 2014 UCC28251

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Description (continued)
  6. 6 Pin Configuration and 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
      1. 8.1.1 UCC28251 Enhancements Over the UCC28250
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  VDD (5/12)
      2. 8.3.2  VREF (Reference Generator) (20/7)
      3. 8.3.3  EN (Enable Pin) (18/5)
      4. 8.3.4  RT (Oscillator Frequency Set and Synchronization) (15/2)
      5. 8.3.5  SP (Synchronous Rectifier Turn-Off to Primary Output Turn-On Dead Time Programming) (13/19)
      6. 8.3.6  PS (Primary Output Turn-Off to Synchronous Rectifier Turn-On Dead Time Programming) (11/18)
      7. 8.3.7  RAMP/CS (PWM Ramp Input or Current Sense Input) (16/3)
        1. 8.3.7.1 RAMP: Voltage Mode Control With Feed-Forward Operation
        2. 8.3.7.2 CS: Current Mode Control
      8. 8.3.8  REF/EA+ (1/8)
      9. 8.3.9  FB/EA- (2/9)
      10. 8.3.10 COMP (3/10)
      11. 8.3.11 VSENSE (14/1)
      12. 8.3.12 SS (Soft Start Programming Pin) (13/20)
      13. 8.3.13 ILIM (Current Limit for Cycle-by-Cycle Over-Current Protection) (17/4)
      14. 8.3.14 HICC (10/17)
      15. 8.3.15 OVP/OTP (19/6)
      16. 8.3.16 OUTA (9/16) and OUTB (8/15)
      17. 8.3.17 SRA (7/14) and SRB (6/13)
      18. 8.3.18 GND (4/11)
    4. 8.4 Device Functional Modes
  9. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Error Amplifier and PWM Generation
      2. 9.1.2 Prebiased Start Up
        1. 9.1.2.1 Secondary-Side Control
        2. 9.1.2.2 Primary-Side Control
      3. 9.1.3 Voltage Mode Control and Input Voltage Feed-Forward
        1. 9.1.3.1 Condition 1
        2. 9.1.3.2 Condition 2
        3. 9.1.3.3 Condition 3
      4. 9.1.4 Peak Current Mode Control
      5. 9.1.5 Cycle-by-Cycle Current Limit and Hiccup Mode Protection
    2. 9.2 Typical Applications
      1. 9.2.1 Circuit Diagram in Design Example
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
          1. 9.2.1.2.1 Step 1: Power Stage Design
          2. 9.2.1.2.2 Step 2: Feedback Loop Design
          3. 9.2.1.2.3 Step 3: Programming The Device
            1. 9.2.1.2.3.1 Step 3-1
            2. 9.2.1.2.3.2 Step 3-2: Determine Ramp Resistance and Capacitance
          4. 9.2.1.2.4 Step 3-3: Determine Soft-Start Capacitance
          5. 9.2.1.2.5 Step 3-4: Determine Dead-Time Resistance
          6. 9.2.1.2.6 Step 3-5: Determine OCP Hiccup Off-Time Capacitance
          7. 9.2.1.2.7 Step 3-6: Determine Primary-Side OVP Resistance
          8. 9.2.1.2.8 Step 3-7: Select Capacitance for VDD and VREF
        3. 9.2.1.3 Application Curves
      2. 9.2.2 Secondary-Side Half-Bridge Controller With Synchronous Rectification
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
    3. 11.3 Thermal Protection
  12. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Trademarks
    3. 12.3 Electrostatic Discharge Caution
    4. 12.4 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

5 Description (continued)

Externally programmable soft-start, used in conjunction with an internal pre-biased startup circuit, allows the controller to gradually reach a steady-state operating point under all output conditions. The UCC28251 can be configured for primary or secondary-side control and either voltage or current mode control can be implemented.

The oscillator operates at frequencies up to 1.8 MHz, and can be synchronized to an external clock. Input voltage feedforward, cycle-by-cycle current limit, and a programmable hiccup timer allow the system to stay within a safe operation range. Input voltage, output voltage and temperature protection can be implemented. Dead time between primary-side switch and secondary-side synchronous rectifiers can be independently programmed.