SNAS874C December   2024  – August 2026 LMR60440-Q1

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 Enable and Undervoltage Lockout (UVLO)
      2. 7.3.2 Soft Start and Recovery from Dropout
      3. 7.3.3 Frequency Selection With RT
      4. 7.3.4 MODE/SYNC Pin Control
      5. 7.3.5 Output Voltage Selection
      6. 7.3.6 Current Limit
      7. 7.3.7 Hiccup Mode
      8. 7.3.8 Power-Good Function
      9. 7.3.9 Spread Spectrum
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown
      2. 7.4.2 Active Mode
        1. 7.4.2.1 Continuous Conduction Mode (CCM)
        2. 7.4.2.2 Auto Mode - Light Load Operation
        3. 7.4.2.3 FPWM Operation - Light Load Operation
        4. 7.4.2.4 Minimum On-Time
        5. 7.4.2.5 Dropout
  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 Switching Frequency Selection
        2. 8.2.2.2 Inductor Selection
        3. 8.2.2.3 Output Capacitor Selection
        4. 8.2.2.4 Input Capacitor Selection
        5. 8.2.2.5 Bootstrap Capacitor (CBOOT) Selection
        6. 8.2.2.6 FB Voltage Divider for Adjustable Output Voltages
          1. 8.2.2.6.1 Feedforward Capacitor (CFF) Selection
        7. 8.2.2.7 RPG - PG Pullup Resistor
      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 Ground and Thermal Plane Considerations
      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 Device Nomenclature
    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

8.2.2.3 Output Capacitor Selection

The LMR60440-Q1 is designed to optimize the required output capacitance while also allowing for high performance. This section describes the theory to calculate the required output capacitance to achieve a certain set of design parameters.

The peak current mode control scheme of the LMR60440-Q1 device allows operation over a wide range of inductor and output capacitor combinations. The output capacitance is responsible for maintaining the desired output voltage during operation. The output capacitance impacts several key performance factors including:

  • The amount of output voltage ripple during steady state operation
  • The overshoot and undershoot of the output voltage when a load transient occurs
  • Loop stability

During steady state operation, the inductor supplies a triangular current to the load. The AC portion of this triangular current is filtered out by the output capacitance while the DC portion passes through to the load. The AC current through the output capacitance and the equivalent series resistance (ESR) of this capacitance both contribute to the output voltage ripple. Use the following equation to estimate the amount of peak to peak output voltage ripple required for a given output capacitance:

Equation 10. V r i p p l e ≈ Δ I L × E S R 2 + 1 8 × f s w × C O U T 2

Where:

  • ΔIL = the peak to peak inductor current

Refer to Table 8-2 for typical output capacitor values for 3.3V and 5V output voltage applications. In this example, a single 22μF multilayer ceramic capacitor is used. For other output voltage and switching frequency designs, WEBENCH can be used as a starting point for selecting the value of the output capacitor.

In practice, the output capacitor has the most influence on the transient response and loop phase margin. Load transient testing and bode plots are the best way to validate any given design and must always be completed before the application goes into production. In addition to the required output capacitance, a small ceramic capacitor placed on the output can help reduce high-frequency noise. Small-case size ceramic capacitors in the range of 1nF to 100nF can be very helpful in reducing spikes on the output caused by inductor and board parasitics.

Most ceramic capacitors deliver far less capacitance than the rating of the capacitor indicates. Be sure to check any capacitor selected for initial accuracy, temperature derating, and voltage derating. Table 8-2 has been generated assuming typical derating of 16V, X7R, automotive grade capacitors. If lower voltage rated, non-automotive grade, or lower temperature rated capacitors are used, more capacitors than listed are likely to be needed.