SNVS726F July   2011  – March 2018 LM25118

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Schematic
      2.      Efficiency vs VIN and IOUT, VOUT = 12 V
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin Functions
  6. 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
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 UVLO
      2. 7.3.2 Oscillator and Sync Capability
      3. 7.3.3 Error Amplifier and PWM Comparator
      4. 7.3.4 Ramp Generator
      5. 7.3.5 Current Limit
      6. 7.3.6 Maximum Duty Cycle
      7. 7.3.7 Soft Start
      8. 7.3.8 HO Output
      9. 7.3.9 Thermal Protection
    4. 7.4 Device Functional Modes
      1. 7.4.1 Buck Mode Operation: VIN > VOUT
      2. 7.4.2 Buck-Boost Mode Operation: VIN ≊ VOUT
      3. 7.4.3 High Voltage Start-Up Regulator
      4. 7.4.4 Enable
  8. 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  R7 = RT
        3. 8.2.2.3  Inductor Selection – L1
        4. 8.2.2.4  R13 = RSENSE
        5. 8.2.2.5  C15 = CRAMP
        6. 8.2.2.6  Inductor Current Limit Calculation
        7. 8.2.2.7  C9 - C12 = Output Capacitors
        8. 8.2.2.8  D1
        9. 8.2.2.9  D4
        10. 8.2.2.10 C1 – C5 = Input Capacitors
        11. 8.2.2.11 C20
        12. 8.2.2.12 C8
        13. 8.2.2.13 C16 = CSS
        14. 8.2.2.14 R8, R9
        15. 8.2.2.15 R1, R3, C21
        16. 8.2.2.16 R2
        17. 8.2.2.17 Snubber
        18. 8.2.2.18 Error Amplifier Configuration
          1. 8.2.2.18.1 R4, C18, C17
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
    1. 9.1 Bias Power Dissipation Reduction
    2. 9.2 Thermal Considerations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Development Support
        1. 11.1.1.1 Custom Design With WEBENCH® Tools
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Community Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

8.2.2.9 D4

A Schottky type recirculating diode is required for all LM25118 applications. The near ideal reverse recovery characteristics and low forward voltage drop are particularly important diode characteristics for high input voltage and low output voltage applications. The reverse recovery characteristic determines how long the current surge lasts each cycle when the buck switch is turned on. The reverse recovery characteristics of Schottky diodes minimize the peak instantaneous power in the buck switch during the turn-on transition. The reverse breakdown rating of the diode should be selected for the maximum VIN plus some safety margin.

The forward voltage drop has a significant impact on the conversion efficiency, especially for applications with a low output voltage. Rated current for diodes vary widely from various manufacturers. For the LM25118 this current is user selectable through the current sense resistor value. Assuming a worst-case, 0.6-V drop across the diode, the maximum diode power dissipation can be high. The diode should have a voltage rating of VIN and a current rating of IOUT. A conservative design would at least double the advertised diode rating because specifications between manufacturers vary. For the reference design, a 100-V, 10-A Schottky in a D2PAK package was selected.