SNVSAX8 April   2018 LM3478Q-Q1

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Typical High Efficiency Step-Up (Boost) Converter
  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 - LM3478Q-Q1
    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 Overvoltage Protection
      2. 7.3.2 Slope Compensation Ramp
      3. 7.3.3 Frequency Adjust/Shutdown
      4. 7.3.4 Short-Circuit Protection
    4. 7.4 Device Functional Modes
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Typical High Efficiency Step-Up (Boost) Converter
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1  Custom Design with WEBENCH Tools
          2. 8.2.1.2.2  Power Inductor Selection
          3. 8.2.1.2.3  Programming the Output Voltage
          4. 8.2.1.2.4  Setting the Current Limit
          5. 8.2.1.2.5  Current Limit with External Slope Compensation
          6. 8.2.1.2.6  Power Diode Selection
          7. 8.2.1.2.7  Power MOSFET Selection
          8. 8.2.1.2.8  Input Capacitor Selection
          9. 8.2.1.2.9  Output Capacitor Selection
          10. 8.2.1.2.10 Compensation
        3. 8.2.1.3 Application Curves
      2. 8.2.2 Typical SEPIC Converter
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
          1. 8.2.2.2.1 Power MOSFET Selection
          2. 8.2.2.2.2 Power Diode Selection
          3. 8.2.2.2.3 Selection of Inductors L1 and L2
          4. 8.2.2.2.4 Sense Resistor Selection
          5. 8.2.2.2.5 Sepic Capacitor Selection
          6. 8.2.2.2.6 Input Capacitor Selection
          7. 8.2.2.2.7 Output Capacitor Selection
        3. 8.2.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Custom Design with WEBENCH Tools
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Documentation Support
      1. 11.3.1 Related Documentation
    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

8.2.2.2.1 Power MOSFET Selection

As in a boost converter, parameters governing the selection of the MOSFET are the minimum threshold voltage, VTH(MIN), the on-resistance, RDS(ON), the total gate charge, Qg, the reverse transfer capacitance, CRSS, and the maximum drain to source voltage, VDS(MAX). The peak switch voltage in a SEPIC is given using Equation 35.

Equation 35. VSW(PEAK) = VIN + VOUT + VDIODE

The selected MOSFET should satisfy the condition:

Equation 36. VDS(MAX)> VSW(PEAK)

The peak switch current is given using Equation 37.

Equation 37. LM3478Q-Q1 10135569.png

The RMS current through the switch is given using Equation 38.

Equation 38. LM3478Q-Q1 10135570.png