SLUSFO3 November   2024 LMR51603

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison Table
  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 Fixed Frequency Peak Current Mode Control
      2. 7.3.2 Adjustable Output Voltage
      3. 7.3.3 Enable
      4. 7.3.4 Minimum ON Time, Minimum OFF Time, and Frequency Foldback
      5. 7.3.5 Bootstrap Voltage
      6. 7.3.6 Overcurrent and Short-Circuit Protection
      7. 7.3.7 Soft Start
      8. 7.3.8 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown Mode
      2. 7.4.2 Active Mode
      3. 7.4.3 CCM Mode
      4. 7.4.4 Light Load Operation (PFM Version)
      5. 7.4.5 Light-Load Operation (FPWM Version)
  9. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Custom Design With WEBENCH® Tools
        2. 8.2.2.2 Output Voltage Setpoint
        3. 8.2.2.3 Switching Frequency
        4. 8.2.2.4 Inductor Selection
        5. 8.2.2.5 Output Capacitor Selection
        6. 8.2.2.6 Input Capacitor Selection
        7. 8.2.2.7 Bootstrap Capacitor
        8. 8.2.2.8 Undervoltage Lockout Setpoint
        9. 8.2.2.9 Replacing Non-Sync Buck Converter
      3. 8.2.3 Application Curves
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
        1. 8.4.1.1 Compact Layout for EMI Reduction
        2. 8.4.1.2 Feedback Resistors
      2. 8.4.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Device Support
      1. 9.1.1 Third-Party Products Disclaimer
      2. 9.1.2 Development Support
        1. 9.1.2.1 Custom Design With WEBENCH® Tools
    2. 9.2 Documentation Support
      1. 9.2.1 Related Documentation
    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

8.2.2.8 Undervoltage Lockout Setpoint

The system undervoltage lockout (UVLO) is adjusted using the external voltage divider network of RENT and RENB. The UVLO has two thresholds, one for power up when the input voltage is rising and one for power down or brown outs when the input voltage is falling. Equation 13 can be used to determine the VIN UVLO level.

Equation 13. VIN_RISING=VENH×REBT+RENBRENB

The EN rising threshold (VEN(R)) for LMR51603 is set to be 1.227V (typical). Choose a value of 200kΩ for RENB to minimize input current from the supply. If the desired VIN rising UVLO level is at 6.0V (typical), then the value of RENT can be calculated using Equation 14:

Equation 14. RENT=(VIN_RISINGVEN(R)-1)×RENB

The above equation yields a value of 778kΩ, a standard value of 768kΩ is selected. The resulting VIN falling UVLO threshold, equal to 4.84V, can be calculated by Equation 15 where EN falling threshold (VEN(F)) for LMR51603 is set to be 1.0V (typical).

Equation 15. VIN_FALLING=VEN(F)×REBT+RENBRENB