SNAS894B July   2025  – December 2025 LMR60460-Q1

PRODMIX  

  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 Auto Mode Operation
        2. 7.4.2.2 Continuous Conduction Mode (CCM)
        3. 7.4.2.3 FPWM 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
    1. 11.1 Tape and Reel Information

8.2.2.2 Inductor Selection

The parameters for selecting the inductor are the inductance and the saturation current. The inductance is based on the desired peak-to-peak current ripple during steady-state operation and is normally chosen to be in the range of 20% to 40% of the maximum output current. Note that when selecting the ripple current for applications with much smaller maximum load than the maximum available from the device, use the maximum device current. Use Equation 8 to determine the value of the desired inductance. The constant K refers to the percentage of the inductor current ripple. For this example, choose K = 0.3.

Equation 8. L = ( V I N - V O U T ) f s w × K × I O U T m a x × V O U T V I N

The above equation gives the value of inductance as 3.4μH. Select the standard value of 3.3μH.

Ideally, the saturation current rating of the inductor is at least as large as the high-side switch current limit, IHS-LIM (see also Section 6.5). This size makes sure that the inductor does not saturate even during a short circuit on the output. When the inductor core saturates, the inductance falls to a very low value, causing the inductor current to rise very rapidly. Although the valley current limit, ILS-LIM, is designed to reduce the risk of current runaway, a saturated inductor can cause the current to rise to high values very rapidly. This action can lead to component damage. Do not allow the inductor to saturate. Inductors with a ferrite core material have very hard saturation characteristics, but usually have lower core losses than powered iron cores. Powered iron cores exhibit a soft saturation, allowing some relaxation in the current rating of the inductor. However, powdered iron cores have more core losses at frequency above about 1MHz. In any case, the inductor saturation current must not be less than the maximum peak inductor current at full load.

Use Equation 9 to find the minimum inductance value to avoid subharmonic oscillations:

Equation 9. Lmin=M×VOUTfsw

Where:

M = 0.18