SNVSAW8E March   2020  – April 2022 LM62440-Q1

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Description (continued)
  6. 6 Device Comparison Table
  7. 7 Pin Configuration and Functions
  8. 8 Specifications
    1. 8.1 Absolute Maximum Ratings
    2. 8.2 ESD Ratings
    3. 8.3 Recommended Operating Conditions
    4. 8.4 Thermal Information
    5. 8.5 Electrical Characteristics
    6. 8.6 Timing Characteristics
    7. 8.7 Systems Characteristics
    8. 8.8 Typical Characteristics
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1  EN Uses for Enable and VIN UVLO
      2. 9.3.2  MODE/SYNC Pin Operation
        1. 9.3.2.1 Level-Dependent MODE/SYNC Pin Control
        2. 9.3.2.2 Pulse-Dependent MODE/SYNC Pin Control
        3. 9.3.2.3 Clock Locking
      3. 9.3.3  PGOOD Output Operation
      4. 9.3.4  Internal LDO, VCC UVLO, and BIAS Input
      5. 9.3.5  Bootstrap Voltage and VCBOOT-UVLO (CBOOT Pin)
      6. 9.3.6  Adjustable SW Node Slew Rate
      7. 9.3.7  Spread Spectrum
      8. 9.3.8  Soft Start and Recovery From Dropout
      9. 9.3.9  Output Voltage Setting
      10. 9.3.10 Overcurrent and Short Circuit Protection
      11. 9.3.11 Thermal Shutdown
      12. 9.3.12 Input Supply Current
    4. 9.4 Device Functional Modes
      1. 9.4.1 Shutdown Mode
      2. 9.4.2 Standby Mode
      3. 9.4.3 Active Mode
        1. 9.4.3.1 CCM Mode
        2. 9.4.3.2 Auto Mode – Light-Load Operation
          1. 9.4.3.2.1 Diode Emulation
          2. 9.4.3.2.2 Frequency Reduction
        3. 9.4.3.3 FPWM Mode – Light-Load Operation
        4. 9.4.3.4 Minimum On-Time (High Input Voltage) Operation
        5. 9.4.3.5 Dropout
  10. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
        1. 10.2.2.1  Choosing the Switching Frequency
        2. 10.2.2.2  Setting the Output Voltage
        3. 10.2.2.3  Inductor Selection
        4. 10.2.2.4  Output Capacitor Selection
        5. 10.2.2.5  Input Capacitor Selection
        6. 10.2.2.6  BOOT Capacitor
        7. 10.2.2.7  BOOT Resistor
        8. 10.2.2.8  VCC
        9. 10.2.2.9  BIAS
        10. 10.2.2.10 CFF and RFF Selection
        11. 10.2.2.11 External UVLO
      3. 10.2.3 Application Curves
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
      1. 12.1.1 Ground and Thermal Considerations
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Documentation Support
      1. 13.1.1 Related Documentation
    2. 13.2 Receiving Notification of Documentation Updates
    3. 13.3 Support Resources
    4. 13.4 Trademarks
    5. 13.5 Electrostatic Discharge Caution
    6. 13.6 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

Package Options

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

The LM62440-Q1 reduces frequency whenever output voltage is high. This function is enabled whenever Comp, an internal signal, is low and there is an offset between the regulation set point of FB and the voltage applied to FB. The net effect is that there is larger output impedance while lightly loaded in auto mode than in normal operation. Output voltage must be approximately 1% high when the part is completely unloaded.

GUID-FA99BD8B-2624-444B-8668-B7BF52CB3C6A-low.gif
In auto mode, once output current drops below approximately 1/10th the rated current of the part, output resistance increases so that output voltage is 1% high while the buck is completely unloaded.
Figure 9-23 Steady State Output Voltage Versus Output Current in Auto Mode

In PFM operation, a small DC positive offset is required on the output voltage to activate the PFM detector. The lower the frequency in PFM, the more DC offset is needed on VOUT. If the DC offset on VOUT is not acceptable, a dummy load at VOUT or FPWM Mode can be used to reduce or eliminate this offset.