SNVS676I August   2010  – April  2018 LM5119

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Application Circuit
  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
      2. 7.3.2  UVLO
      3. 7.3.3  Enable 2
      4. 7.3.4  Oscillator and Sync Capability
      5. 7.3.5  Error Amplifiers and PWM Comparators
      6. 7.3.6  Ramp Generator
      7. 7.3.7  Current Limit
      8. 7.3.8  Hiccup Mode Current Limiting
      9. 7.3.9  Soft Start
      10. 7.3.10 HO and LO Output Drivers
      11. 7.3.11 Maximum Duty Cycle
      12. 7.3.12 Thermal Protection
    4. 7.4 Device Functional Modes
      1. 7.4.1 Diode Emulation
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Miscellaneous Functions
      2. 8.1.2 Interleaved Two-Phase Operation
      3. 8.1.3 Interleaved 4-Phase Operation
    2. 8.2 Typical Applications
      1. 8.2.1 Dual-output Design Example
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1  Timing Resistor
          2. 8.2.1.2.2  Output Inductor
          3. 8.2.1.2.3  Current Sense Resistor
          4. 8.2.1.2.4  Ramp Resistor and Ramp Capacitor
          5. 8.2.1.2.5  Output Capacitors
          6. 8.2.1.2.6  Input Capacitors
          7. 8.2.1.2.7  VCC Capacitor
          8. 8.2.1.2.8  Bootstrap Capacitor
          9. 8.2.1.2.9  Soft-Start Capacitor
          10. 8.2.1.2.10 Restart Capacitor
          11. 8.2.1.2.11 Output Voltage Divider
          12. 8.2.1.2.12 UVLO Divider
            1. 8.2.1.2.12.1 MOSFET Selection
          13. 8.2.1.2.13 MOSFET Snubber
          14. 8.2.1.2.14 Error Amplifier Compensation
        3. 8.2.1.3 Application Curves
      2. 8.2.2 Two-Phase Design Example
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
        3. 8.2.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Switching Jitter Root Causes and Solutions
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Receiving Notification of Documentation Updates
    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

8.2.1.2.4 Ramp Resistor and Ramp Capacitor

The value of ramp capacitor (CRAMP) must be less than 2 nF to allow full discharge between cycles by the discharge switch internal to the LM5119. A good-quality, thermally-stable ceramic capacitor with 5% or less tolerance is recommended. For this design the value of CRAMP was set at the standard capacitor value of 820 pF. With the inductor, sense resistor and the K factor selected, the value of the ramp resistor (RRAMP) can be calculated with Equation 19 as the example (Equation 20). The standard value of 73.2 kΩ was selected.

Equation 19. LM5119 30124040.gif
Equation 20. LM5119 30124041.gif