SLUSEP7 December   2022 LMR51440 , LMR51450

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2.     ESD Ratings
    3. 7.2 Recommended Operating Conditions
    4. 7.3 Thermal Information
    5. 7.4 Electrical Characteristics
    6. 7.5 System Characteristics
    7. 7.6 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  Fixed Frequency Peak Current Mode Control
      2. 8.3.2  Adjustable Output Voltage
      3. 8.3.3  Enable
      4. 8.3.4  Switching Frequency
      5. 8.3.5  Power-Good Flag Output
      6. 8.3.6  Minimum ON-Time, Minimum OFF-Time, and Frequency Foldback
      7. 8.3.7  Bootstrap Voltage
      8. 8.3.8  Overcurrent and Short-Circuit Protection
      9. 8.3.9  Soft Start
      10. 8.3.10 Thermal Shutdown
    4. 8.4 Device Functional Modes
      1. 8.4.1 Shutdown Mode
      2. 8.4.2 Active Mode
      3. 8.4.3 CCM Mode
      4. 8.4.4 Light-Load Operation (PFM Version)
      5. 8.4.5 Light-Load Operation (FPWM Version)
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Output Voltage Set-Point
        2. 9.2.2.2 Switching Frequency
        3. 9.2.2.3 Inductor Selection
        4. 9.2.2.4 Output Capacitor Selection
        5. 9.2.2.5 Input Capacitor Selection
        6. 9.2.2.6 Bootstrap Capacitor
        7. 9.2.2.7 Undervoltage Lockout Set-Point
      3. 9.2.3 Application Curves
    3. 9.3 Best Design Practices
    4. 9.4 Power Supply Recommendations
    5. 9.5 Layout
      1. 9.5.1 Layout Guidelines
        1. 9.5.1.1 Compact Layout for EMI Reduction
        2. 9.5.1.2 Feedback Resistors
      2. 9.5.2 Layout Example
  10. 10Device and Documentation Support
    1. 10.1 Device Support
      1. 10.1.1 Development Support
        1. 10.1.1.1 Custom Design With WEBENCH® Tools
    2. 10.2 Documentation Support
      1. 10.2.1 Related Documentation
    3. 10.3 Receiving Notification of Documentation Updates
    4. 10.4 Support Resources
    5. 10.5 Trademarks
    6. 10.6 Electrostatic Discharge Caution
    7. 10.7 Glossary
  11. 11Mechanical, Packaging, and Orderable Information

Package Options

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

8.3.4 Switching Frequency

The switching frequency of the LMR514x0 can be programmed by the resistor RT from the RT pin and GND pin. To determine the timing resistance for a given switching frequency, use Equation 2 or the curve in Figure 8-4. Table 8-1 gives typical RT values for a given fSW.

Equation 2. RT(kΩ)=30542×fSW(kHz)-1.108
GUID-20221119-SS0I-BVVX-FL7R-TF9GH3VDHWTS-low.pngFigure 8-4 RT Versus Frequency Curve
Table 8-1 Typical Frequency Setting RT Resistance
fSW (kHz)RT (kΩ)
20084.5
400

39.2

495

31.6

500

Open or pull-up to voltage >1.0 V

800

18.2

1000

14.3

1000

Short to GND