SNVS479I January   2007  – April 2026 LM25575

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 Shutdown and Stand-by Mode
      2. 6.3.2 Soft Start
      3. 6.3.3 Thermal Protection
    4. 6.4 Device Functional Modes
      1. 6.4.1 High Voltage Start-Up Regulator
      2. 6.4.2 Oscillator and Sync Capability
      3. 6.4.3 Error Amplifier and PWM Comparator
      4. 6.4.4 Ramp Generator
      5. 6.4.5 Maximum Duty Cycle and Input Drop-out Voltage
      6. 6.4.6 Boost Pin
      7. 6.4.7 Current Limit
  8. 7 Application and Implementation
    1. 7.1 Application Information
      1. 7.1.1 BIas Power Dissipation Reduction
    2. 7.2 Typical Application
      1. 7.2.1 Typical Schematic for High Frequency (1MHz) Application
      2. 7.2.2 Design Requirements
      3. 7.2.3 Detailed Design Procedure
        1. 7.2.3.1  Custom Design With WEBENCH® Tools
        2. 7.2.3.2  R3 (RT)
        3. 7.2.3.3  L1
        4. 7.2.3.4  C3 (CRAMP)
        5. 7.2.3.5  C9, C10
        6. 7.2.3.6  D1
        7. 7.2.3.7  C1, C2
        8. 7.2.3.8  C8
        9. 7.2.3.9  C7
        10. 7.2.3.10 C4
        11. 7.2.3.11 R5, R6
        12. 7.2.3.12 R1, R2, C12
        13. 7.2.3.13 R7, C11
        14. 7.2.3.14 R4, C5, C6
      4. 7.2.4 Application Curves
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
        1. 7.4.1.1 PCB Layout and Thermal Considerations
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Developmental Support
        1. 8.1.1.1 Custom Design With WEBENCH® Tools
    2. 8.2 Receiving Notification of Documentation Updates
    3. 8.3 Support Resources
    4. 8.4 Trademarks
    5. 8.5 Electrostatic Discharge Caution
    6. 8.6 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

Package Options

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

7.2.3.3 L1

The inductor value is determined based on the operating frequency, load current, ripple current, and the minimum and maximum input voltage (VIN(min), VIN(max)).

LM25575 Inductor Current WaveformFigure 7-3 Inductor Current Waveform

To keep the circuit in continuous conduction mode (CCM), the maximum ripple current IRIPPLE must be less than twice the minimum load current, or 0.4 Ap-p. Using this value of ripple current, the value of inductor (L1) is calculated using the following:

Equation 6. LM25575
Equation 7. LM25575

This procedure provides a guide to select the value of L1. The nearest standard value (47µH) will be used. L1 must be rated for the peak current (IPK+) to prevent saturation. During normal loading conditions, the peak current occurs at maximum load current plus maximum ripple. During an overload condition the peak current is limited to 2.1A nominal (2.5A maximum). The selected inductor (see Table 7-1) has a conservative 3.25 Amp saturation current rating. For this manufacturer, the saturation rating is defined as the current necessary for the inductance to reduce by 30%, at 20°C.