SNVSB96 July   2019 LM3424-Q1

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
    1.     Typical Boost Application Circuit
  3. 3 Description
  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  Current Regulators
      2. 7.3.2  Peak Current Mode Control
      3. 7.3.3  Average LED Current
      4. 7.3.4  Thermal Foldback and Analog Dimming
      5. 7.3.5  Current Sense and Current Limit
      6. 7.3.6  Slope Compensation
      7. 7.3.7  Control Loop Compensation
      8. 7.3.8  Start-Up Regulator and Soft-Start
      9. 7.3.9  Overvoltage Lockout (OVLO)
      10. 7.3.10 Input Undervoltage Lockout (UVLO)
        1. 7.3.10.1 UVLO Only
        2. 7.3.10.2 PWM Dimming and UVLO
      11. 7.3.11 PWM Dimming
      12. 7.3.12 Thermal Shutdown
    4. 7.4 Device Functional Modes
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Inductor
      2. 8.1.2 LED Dynamic Resistance
      3. 8.1.3 Output Capacitor
      4. 8.1.4 Input Capacitors
      5. 8.1.5 Main MOSFET and Dimming MOSFET
      6. 8.1.6 Re-Circulating Diode
      7. 8.1.7 Switching Frequency
    2. 8.2 Typical Applications
      1. 8.2.1 Basic Topology Schematics
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1  Operating Point
          2. 8.2.1.2.2  Switching Frequency
          3. 8.2.1.2.3  Average LED Current
          4. 8.2.1.2.4  Thermal Foldback
          5. 8.2.1.2.5  Inductor Ripple Current
          6. 8.2.1.2.6  LED Ripple Current
          7. 8.2.1.2.7  Peak Current Limit
          8. 8.2.1.2.8  Slope Compensation
          9. 8.2.1.2.9  Loop Compensation
          10. 8.2.1.2.10 Input Capacitance
          11. 8.2.1.2.11 NFET
          12. 8.2.1.2.12 Diode
          13. 8.2.1.2.13 Output OVLO
          14. 8.2.1.2.14 Input UVLO
          15. 8.2.1.2.15 Soft-Start
          16. 8.2.1.2.16 PWM Dimming Method
          17. 8.2.1.2.17 Analog Dimming Method
      2. 8.2.2 Buck-Boost Application
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
          1. 8.2.2.2.1  Operating Point
          2. 8.2.2.2.2  Switching Frequency
          3. 8.2.2.2.3  Average LED Current
          4. 8.2.2.2.4  Thermal Foldback
          5. 8.2.2.2.5  Inductor Ripple Current
          6. 8.2.2.2.6  Output Capacitance
          7. 8.2.2.2.7  Peak Current Limit
          8. 8.2.2.2.8  Slope Compensation
          9. 8.2.2.2.9  Loop Compensation
          10. 8.2.2.2.10 Input Capacitance
          11. 8.2.2.2.11 NFET
          12. 8.2.2.2.12 Diode
          13. 8.2.2.2.13 Input UVLO
          14. 8.2.2.2.14 Output OVLO
          15. 8.2.2.2.15 Soft-Start
        3. 8.2.2.3 Application Curve
      3. 8.2.3 Boost Application
        1. 8.2.3.1 Design Requirements
        2. 8.2.3.2 Detailed Design Procedure
      4. 8.2.4 Buck-Boost Application
        1. 8.2.4.1 Design Requirements
        2. 8.2.4.2 Detailed Design Procedures
      5. 8.2.5 Boost Application
        1. 8.2.5.1 Design Requirements
        2. 8.2.5.2 Detailed Design Procedure
      6. 8.2.6 Buck-Boost Application
        1. 8.2.6.1 Design Requirements
        2. 8.2.6.2 Detailed Design Procedure
      7. 8.2.7 Buck Application
        1. 8.2.7.1 Design Requirements
        2. 8.2.7.2 Detailed Design Procedure
      8. 8.2.8 Buck-Boost Application
        1. 8.2.8.1 Design Requirements
        2. 8.2.8.2 Detailed Design Procedure
      9. 8.2.9 SEPIC Application
        1. 8.2.9.1 Design Requirements
        2. 8.2.9.2 Detailed Design Procedure
  9. 9 Power Supply Recommendations
    1. 9.1 Input Supply Current Limit
  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 Third-Party Products Disclaimer
    2. 11.2 Community Resources
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

8.1.3 Output Capacitor

For boost and buck-boost regulators, the output capacitor (CO) provides energy to the load when the recirculating diode (D1) is reverse biased during the first switching subinterval. An output capacitor in a buck topology will simply reduce the LED current ripple (ΔiLED-PP) below the inductor current ripple (ΔiL-PP). In all cases, CO is sized to provide a desired ΔiLED-PP. As mentioned in the Inductor section, ΔiLED-PP is recommended by manufacturers to be less than 40% of the average LED current (ILED).

CO should be carefully chosen to account for derating due to temperature and operating voltage. It must also have the necessary RMS current rating. Ceramic capacitors are the best choice due to their high ripple current rating, long lifetime, and good temperature performance. An X7R dieletric rating is suggested.