SNVS359E May   2005  – December 2014 LM5021

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operation Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Typical Performance Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 PWM Comparator and Slope Compensation
      2. 7.3.2 Current Limit and Current Sense
      3. 7.3.3 Oscillator, Shutdown and Sync Capability
      4. 7.3.4 Gate Driver and Max Duty Cycle Limit
      5. 7.3.5 Soft-Start
      6. 7.3.6 Hiccup Mode Overload Current Limiting
      7. 7.3.7 Skip Cycle Operation
    4. 7.4 Device Functional Modes
      1. 7.4.1 Operation With VIN Below 20 V
      2. 7.4.2 Operation in Soft Start
      3. 7.4.3 Operation Under Normal Conditions
      4. 7.4.4 Operation in Skip Cycle
      5. 7.4.5 Operation at Overload
      6. 7.4.6 Operation in Hiccup Mode
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Startup Circuit
      2. 8.1.2 Relationship Between Input Capacitor CIN and VCC Capacitor CVCC
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Primary Bulk Capacitance
        2. 8.2.2.2 Transformer
        3. 8.2.2.3 Main Switch FET and Output Rectifier
        4. 8.2.2.4 Timing Resistor
        5. 8.2.2.5 Soft-Start Time
        6. 8.2.2.6 Current Sensing Network
          1. 8.2.2.6.1 Gate Drive Resistor
          2. 8.2.2.6.2 VCC Capacitor
          3. 8.2.2.6.3 Startup Circuit
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Trademarks
    2. 11.2 Electrostatic Discharge Caution
    3. 11.3 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

1 Features

  • Ultra-low Startup Current (25 µA Maximum)
  • Current Mode Control
  • Skip Cycle Mode for Low Standby Power
  • Single Resistor Programmable Oscillator
  • Synchronizable Oscillator
  • Adjustable Soft-Start
  • Integrated 0.7-A Peak Gate Driver
  • Direct Opto-Coupler Interface
  • Maximum Duty Cycle Limiting (80% for LM5021-1 or 50% for LM5021-2)
  • Slope Compensation (LM5021-1 Only)
  • Undervoltage Lockout (UVLO) with Hysteresis
  • Cycle-by-Cycle Overcurrent Protection
  • Hiccup Mode for Continuous Overload Protection
  • Leading Edge Blanking of Current Sense Signal
  • Packages: VSSOP-8 or PDIP-8

2 Applications

  • DCM/CCM Flyback Converters
  • Industrial Power Conversion
  • SMPS for Smart Meters and Audio Amplifiers
  • Building Automation and White Goods SMPS
  • Isolated Telecom Power Supplies

3 Description

The LM5021 off-line pulse width modulation (PWM) controller contains all of the features needed to implement highly efficient off-line single-ended flyback and forward power converters using current-mode control. The LM5021 features include an ultra-low (25 µA) start-up current, which minimizes power losses in the high voltage start-up network. A skip cycle mode reduces power consumption with light loads for energy conserving applications (ENERGY STAR®, CECP, and so forth). Additional features include under-voltage lockout, cycle-by-cycle current limit, hiccup mode overload protection, slope compensation, soft-start and oscillator synchronization capability. This high performance 8-pin IC has total propagation delays less than 100 ns and a 1-MHz capable oscillator that is programmed with a single resistor.

Device Information(1)

PART NUMBER PACKAGE BODY SIZE (NOM)
LM5021 VSSOP (8) 3.00 mm × 3.00 mm
PDIP (8) 9.81 mm × 6.35 mm
  1. For all available packages, see the orderable addendum at the end of the datasheet.

Simplified Application Diagram

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