SNVSB28 December   2017 LM25575-Q1

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Application Schematic
  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 Switching Characteristics
    7. 6.7 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 High Voltage Start-Up Regulator
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown and Stand-by Mode
      2. 7.4.2 Error Amplifier and PWM Comparator
      3. 7.4.3 Ramp Generator
      4. 7.4.4 Maximum Duty Cycle and Input Drop-out Voltage
      5. 7.4.5 Current Limit
      6. 7.4.6 Soft-Start
      7. 7.4.7 Boost Pin
      8. 7.4.8 Thermal Protection
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1  External Components
      2. 8.1.2  R3 (RT)
      3. 8.1.3  L1
      4. 8.1.4  C3 (CRAMP)
      5. 8.1.5  C9, C10
      6. 8.1.6  D1
      7. 8.1.7  C1, C2
      8. 8.1.8  C8
      9. 8.1.9  C7
      10. 8.1.10 C4
      11. 8.1.11 R5, R6
      12. 8.1.12 R1, R2, C12
      13. 8.1.13 R7, C11
      14. 8.1.14 R4, C5, C6
      15. 8.1.15 BIas Power Dissipation Reduction
    2. 8.2 Typical Application
      1. 8.2.1 Typical Schematic for High Frequency (1 MHz) Application
  9. 9 Layout
    1. 9.1 Layout Guidelines
      1. 9.1.1 PCB Layout and Thermal Considerations
    2. 9.2 Layout Example
  10. 10Device and Documentation Support
    1. 10.1 Device Support
      1. 10.1.1 Developmental Support
        1. 10.1.1.1 Custom Design With WEBENCH® Tools
    2. 10.2 Receiving Notification of Documentation Updates
    3. 10.3 Community Resources
    4. 10.4 Trademarks
    5. 10.5 Electrostatic Discharge Caution
    6. 10.6 Glossary
  11. 11Mechanical, Packaging, and Orderable Information

Package Options

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

8.1.12 R1, R2, C12

A voltage divider can be connected to the SD pin to set a minimum operating voltage VIN(min) for the regulator. If this feature is required, the easiest approach to select the divider resistor values is to select a value for R1 (between 10 kΩ and 100 kΩ recommended) then calculate R2 from Equation 11:

Equation 11. LM25575-Q1 20212114.gif

Capacitor C12 provides filtering for the divider. The voltage at the SD pin should never exceed 8 V, when using an external set-point divider it may be necessary to clamp the SD pin at high input voltage conditions. The reference design utilizes the full range of the LM25575-Q1 (6 V to 42 V); therefore these components can be omitted. With the SD pin open circuit the LM25575-Q1 responds once the VCC UVLO threshold is satisfied.