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

1 Features

  • Prebiased Startup
  • Synchronous Rectifier Control Outputs with Programmable Delays (Including Zero Delay Support)
  • Voltage Mode Control with Input Voltage Feed-Forward or Current Mode Control
  • Primary or Secondary-Side Control
  • 3.3-V, 1.5% Accurate Reference Output
  • Lower Minimum Operating Frequency
  • 1% Accurate Cycle-by-Cycle Over Current Protection with Matched Duty Cycle Outputs
  • Programmable Soft-Start and Hiccup Restart Timer
  • Thermally Enhanced 4-mm x 4-mm VQFN-20 Package and 20-pin TSSOP Package

2 Applications

  • Half-Bridge, Full-Bridge, Interleaved Forward, and Push-Pull Isolated Converters
  • Telecom and Data-com Power
  • Wireless Base Station Power
  • Server Power
  • Industrial Power Systems

3 Description

The UCC28251 PWM controller is designed for high power density applications that may have stringent prebiased startup requirements. The UCC28251’s integrated synchronous rectifier control outputs target high efficiency and high performance topologies such as half-bridge, full-bridge, interleaved forward, and push-pull. The UCC27210 half bridge drivers and UCC2752x MOSFET drivers used in conjunction with the UCC28251 provide a complete power converter solution.

The UCC28251 is a functional variant of the UCC28250 PWM Controller. While the same basic functionality of the UCC28250 is largely maintained, the UCC28251 is designed to enhance performance in both offline, 400-V input DC-to-DC applications and 48-V input full-bridge or half-bridge applications.

Device Information(1)

PART NUMBER PACKAGE BODY SIZE (NOM)
UCC28251 TSSOP (20) 6.50 mm × 4.40 mm
VQFN (20) 4.00 mm × 4.00 mm
  1. For all available packages, see the orderable addendum at the end of the datasheet.

Simple Application Diagram (400-VIN DC-to-DC Converter)

UCC28251 alt2_lusbd8.gif

Simple Application Diagram (48-VIN DC-to-DC Converter)

UCC28251 alt_lusbd8.gif