SNVSBX7A September   2023  – June 2024 LM70840-Q1 , LM70860-Q1 , LM70880-Q1

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Description (continued)
  6. 5 Pin Configuration and Functions
  7. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Typical Characteristics
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Input Voltage Range (VIN)
      2. 7.3.2  High-Voltage Bias Supply Regulator (VCC, BIAS, VDDA)
      3. 7.3.3  Enable (EN)
      4. 7.3.4  Power-Good Monitor (PG)
      5. 7.3.5  Switching Frequency (RT)
      6. 7.3.6  Dual Random Spread Spectrum (DRSS)
      7. 7.3.7  Soft Start
      8. 7.3.8  Output Voltage Setpoint (FB)
      9. 7.3.9  Minimum Controllable On-Time
      10. 7.3.10 Error Amplifier and PWM Comparator (FB, EXTCOMP)
      11. 7.3.11 Slope Compensation
      12. 7.3.12 Shunt Current Sensing
      13. 7.3.13 Hiccup Mode Current Limiting
      14. 7.3.14 Device Configuration (CONFIG)
      15. 7.3.15 Single-Output Dual-phase Operation
      16. 7.3.16 Pulse Frequency Modulation (PFM) / Synchronization
      17. 7.3.17 Thermal Shutdown (TSD)
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown Mode
      2. 7.4.2 Standby Mode
      3. 7.4.3 Active Mode
      4. 7.4.4 Sleep Mode
  9. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Power Train Components
        1. 8.1.1.1 Buck Inductor
        2. 8.1.1.2 Output Capacitors
        3. 8.1.1.3 Input Capacitors
        4. 8.1.1.4 EMI Filter
      2. 8.1.2 Error Amplifier and Compensation
      3. 8.1.3 Maximum Ambient Temperature
        1. 8.1.3.1 Derating Curves
    2. 8.2 Typical Applications
      1. 8.2.1 Design 1 – High Efficiency, Wide Input, 400-kHz Synchronous Buck Regulator
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 Custom Design With WEBENCH® Tools
          2. 8.2.1.2.2 Custom Design With Excel Quickstart Tool
          3. 8.2.1.2.3 Buck Inductor
          4. 8.2.1.2.4 Current-Sense Resistance
          5. 8.2.1.2.5 Output Capacitors
          6. 8.2.1.2.6 Input Capacitors
          7. 8.2.1.2.7 Frequency Set Resistor
          8. 8.2.1.2.8 Feedback Resistors
          9. 8.2.1.2.9 Compensation Components
        3. 8.2.1.3 Application Curves
      2. 8.2.2 Design 2 – High Efficiency 48V to 12V 400kHz Synchronous Buck Regulator
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
        3. 8.2.2.3 Application Curves
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Thermal Design and Layout
      3. 8.4.3 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Device Support
      1. 9.1.1 Development Support
        1. 9.1.1.1 Custom Design With WEBENCH® Tools
    2. 9.2 Documentation Support
      1. 9.2.1 Related Documentation
        1. 9.2.1.1 PCB Layout Resources
        2. 9.2.1.2 Thermal Design Resources
    3. 9.3 Receiving Notification of Documentation Updates
    4. 9.4 Support Resources
    5. 9.5 Trademarks
    6. 9.6 Electrostatic Discharge Caution
    7. 9.7 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information
    1. 11.1 Tape and Reel Information

8.4.2 Thermal Design and Layout

For a DC/DC converter to be useful over a particular temperature range, the package must allow for the efficient removal of the heat produced while keeping the junction temperature within rated limits. The LM70880-Q1 is available in a small 6-mm × 6-mm 29-pin QFN integrated circuit package to cover a range of application requirements. Thermal Design and Layout summarizes the thermal metrics of this package.

Numerous vias with a 0.3-mm diameter connected from the thermal pads to the internal and solder-side plane or planes are vital to help dissipation. In a multi-layer PCB design, a solid GND plane is typically placed on the PCB layer below the power components. Not only does this action provide a plane for the power stage currents to flow but this action also represents a thermally conductive path away from the heat generating devices.