SNVSB48C April   2018  – October 2019 LMR36006

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Schematic
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
    1.     Pin Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Timing Requirements
    7. 7.7 System Characteristics
    8. 7.8 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Power-Good Flag Output
      2. 8.3.2 Enable and Start-up
      3. 8.3.3 Current Limit and Short Circuit
      4. 8.3.4 Undervoltage Lockout and Thermal Shutdown
    4. 8.4 Device Functional Modes
      1. 8.4.1 Auto Mode
      2. 8.4.2 Dropout
      3. 8.4.3 Minimum Switch On-Time
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design 1: Low Power 24-V, 600-mA PFM Converter
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
          1. 9.2.1.2.1  Custom Design With WEBENCH Tools
          2. 9.2.1.2.2  Choosing the Switching Frequency
          3. 9.2.1.2.3  Setting the Output Voltage
          4. 9.2.1.2.4  Inductor Selection
          5. 9.2.1.2.5  Output Capacitor Selection
          6. 9.2.1.2.6  Input Capacitor Selection
          7. 9.2.1.2.7  CBOOT
          8. 9.2.1.2.8  VCC
          9. 9.2.1.2.9  CFF Selection
            1. 9.2.1.2.9.1 External UVLO
          10. 9.2.1.2.10 Maximum Ambient Temperature
      2. 9.2.2 Application Curves
      3. 9.2.3 Design 2: High Density 24-V, 600-mA PFM Converter
        1. 9.2.3.1 Design Requirements
        2. 9.2.3.2 Application Curves
    3. 9.3 What to Do and What Not to Do
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
      1. 11.1.1 Ground and Thermal Considerations
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Development Support
        1. 12.1.1.1 Custom Design With WEBENCH® Tools
    2. 12.2 Documentation Support
      1. 12.2.1 Related Documentation
    3. 12.3 Receiving Notification of Documentation Updates
    4. 12.4 Support Resources
    5. 12.5 Trademarks
    6. 12.6 Electrostatic Discharge Caution
    7. 12.7 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

8.4.2 Dropout

The dropout performance of any buck regulator is affected by the RDSON of the power MOSFETs, the DC resistance of the inductor, and the maximum duty cycle that the controller can achieve. As the input voltage is reduced to near the output voltage, the off-time of the high-side MOSFET starts to approach the minimum value. Beyond this point the switching may become erratic and/or the output voltage falls out of regulation. To avoid this problem the LMR36006 automatically reduces the switching frequency to increase the effective duty cycle and maintain regulation. In this data sheet the dropout voltage is defined as the difference between the input and output voltage when the output has dropped by 1% of its nominal value. Under this condition the switching frequency has dropped to its minimum value of about 140 kHz. Note that the 0.4 V short circuit detection threshold is not activated when in dropout mode. Typical dropout characteristics can be found in Figure 15 and Figure 16.

LMR36006 D003-tc-drop-out-down-snvsay7-rtm.gifFigure 15. Overall Dropout Characteristic
VOUT = 5 V
LMR36006 LMR36006B-dropout.gifFigure 16. Typical ƒSW vs Output Current
ƒSW = 1000 kHz