SNVS397F September   2005  – December 2025 LM5005

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Switching Characteristics
    7. 5.7 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 High-Voltage Start-Up Regulator
      2. 6.3.2 Shutdown and Standby
      3. 6.3.3 Oscillator and Synchronization Capability
      4. 6.3.4 Error Amplifier and PWM Comparator
      5. 6.3.5 RAMP Generator
      6. 6.3.6 Current Limit
      7. 6.3.7 Soft-Start Capability
      8. 6.3.8 MOSFET Gate Driver
    4. 6.4 Device Functional Modes
      1. 6.4.1 Shutdown Mode
      2. 6.4.2 Standby Mode
      3. 6.4.3 Light-Load Operation
      4. 6.4.4 Thermal Shutdown Protection
  8. 7 Application and Implementation
    1. 7.1 Application Information
      1. 7.1.1 Reducing Bias Power Dissipation
      2. 7.1.2 Input Voltage UVLO Protection
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
        1. 7.2.2.1  Custom Design With WEBENCH® Tools
        2. 7.2.2.2  Frequency Set Resistor (RT)
        3. 7.2.2.3  Inductor (LF)
        4. 7.2.2.4  Ramp Capacitor (CRAMP)
        5. 7.2.2.5  Output Capacitors (COUT)
        6. 7.2.2.6  Schottky Diode (DF)
        7. 7.2.2.7  Input Capacitors (CIN)
        8. 7.2.2.8  VCC Capacitor (CVCC)
        9. 7.2.2.9  Bootstrap Capacitor (CBST)
        10. 7.2.2.10 Soft Start Capacitor (CSS)
        11. 7.2.2.11 Feedback Resistors (RFB1 and RFB2)
        12. 7.2.2.12 RC Snubber (RS and CS)
        13. 7.2.2.13 Compensation Components (RC1, CC1, CC2)
        14. 7.2.2.14 Bill of Materials
      3. 7.2.3 Application Curves
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
        1. 7.4.1.1 PCB Layout for EMI Reduction
        2. 7.4.1.2 Thermal Design
        3. 7.4.1.3 Ground Plane Design
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Third-Party Products Disclaimer
    2. 8.2 Device Support
      1. 8.2.1 Development Support
        1. 8.2.1.1 Custom Design With WEBENCH® Tools
    3. 8.3 Documentation Support
      1. 8.3.1 Related Documentation
        1. 8.3.1.1 PCB Layout Resources
        2. 8.3.1.2 Thermal Design Resources
    4. 8.4 Receiving Notification of Documentation Updates
    5. 8.5 Support Resources
    6. 8.6 Trademarks
    7. 8.7 Electrostatic Discharge Caution
    8. 8.8 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

Package Options

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

7.4.1.2 Thermal Design

As with any power conversion device, the LM5005 dissipates internal power while operating. The effect of the power dissipation is to raise the internal junction temperature of the LM5005 above ambient. The junction temperature (TJ) is a function of the ambient temperature (TA), the power dissipation (PD) and the effective thermal resistance of the device and PCB combination (RθJA). The maximum operating junction temperature for the LM5005 is 125°C, thus establishing a limit on the maximum device power dissipation and therefore the load current at high ambient temperatures. Equation 23 and Equation 24 show the relationships between these parameters.

Equation 23. P D = P O U T × 1 - ƞ ƞ - V F × I O U T × 1 - D - I O U T 2 × R D C R × 1.5
Equation 24. T J = P D × θ J A + T A

An approximation for the inductor power loss in Equation 23 includes a factor of 1.5 for the core losses. Also, if a snubber is used, estimate the power loss by observation of the resistor voltage drop at both turnon and turnoff switching transitions.

High ambient temperatures and large values of RθJA reduce the maximum available output current. If the junction temperature exceeds 165°C, the LM5005 cycles in and out of thermal shutdown. Thermal shutdown can be a sign of inadequate heat-sinking or excessive power dissipation. Improve PCB heat-sinking by using more thermal vias, a larger board, or additional heat-spreading layers within that board.

As stated in the Semiconductor and IC Package Thermal Metrics application note, the values given in Thermal Information are not always valid for design purposes to estimate the thermal performance of the application. The values reported in this table are measured under a specific set of conditions that are seldom obtained in an actual application. The effective RθJA is a critical parameter and depends on many factors (such as power dissipation, air temperature, PCB area, copper heat-sink area, number of thermal vias under the package, air flow, and adjacent component placement). The exposed pad of the LM5005 has a direct thermal connection to PGND. This pad must be soldered directly to the PCB copper ground plane to provide an effective heat-sink and proper electrical connection. Use the documents listed in Documentation Support as a guide for optimized thermal PCB design and estimating RθJA for a given application environment.