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

9 Power Supply Recommendations

The LM5021 is designed to run from a power supply in the range of 7.25 V to 30 V connected to VIN. A capacitor is required from VIN to GND to supply startup energy for the converter. Typical values are a few µF to a few tens of µF. Electrolytic capacitors are acceptable here.

The internal circuits of the controller operate from an internal 8-V regulator that is brought out on VCC. The VCC pin needs a small bypass capacitor, typically 100-nF to 1-µF ceramic, closely coupled to the GND pin for best operation. It is not recommended to directly drive the VCC pin from another power source.

NOTE

It is not recommended that the bias winding be connected to the VCC pin of the LM5021. Doing so can cause the device to operate incorrectly or not at all.