SNVS346H November   2007  – October 2024 LM3481

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
    1.     Pin Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings: LM3481
    3. 5.3 Recommended Operating Ratings
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 Overvoltage Protection
      2. 6.3.2 Bias Voltage
      3. 6.3.3 Slope Compensation Ramp
      4. 6.3.4 Frequency Adjust, Synchronization, and Shutdown
      5. 6.3.5 Undervoltage Lockout (UVLO) Pin
      6. 6.3.6 Short-Circuit Protection
    4. 6.4 Device Functional Modes
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Applications
      1. 7.2.1 Boost Converter
        1. 7.2.1.1 Design Requirements
        2. 7.2.1.2 Detailed Design Procedure
          1. 7.2.1.2.1  Custom Design with WEBENCH Tools
          2. 7.2.1.2.2  Power Inductor Selection
          3. 7.2.1.2.3  Programming the Output Voltage and Output Current
          4. 7.2.1.2.4  Current Limit With Additional Slope Compensation
          5. 7.2.1.2.5  Power Diode Selection
          6. 7.2.1.2.6  Power MOSFET Selection
          7. 7.2.1.2.7  Input Capacitor Selection
          8. 7.2.1.2.8  Output Capacitor Selection
          9. 7.2.1.2.9  Driver Supply Capacitor Selection
          10. 7.2.1.2.10 Compensation
        3. 7.2.1.3 Application Curve
      2. 7.2.2 Typical SEPIC Converter
        1. 7.2.2.1 Design Requirements
        2. 7.2.2.2 Detailed Design Procedure
          1. 7.2.2.2.1 Power MOSFET Selection
          2. 7.2.2.2.2 Power Diode Selection
          3. 7.2.2.2.3 Selection of Inductors L1 and L2
          4. 7.2.2.2.4 Sense Resistor Selection
          5. 7.2.2.2.5 SEPIC Capacitor Selection
          6. 7.2.2.2.6 Input Capacitor Selection
          7. 7.2.2.2.7 Output Capacitor Selection
        3. 7.2.2.3 Application Curve
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Documentation Support
      1. 8.1.1 Custom Design with WEBENCH Tools
      2. 8.1.2 Related Documentation
    2. 8.2 Receiving Notification of Documentation Updates
    3. 8.3 Support Resources
    4. 8.4 Trademarks
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information
7.2.2.2.1 Power MOSFET Selection

As in a boost converter, the 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 by:

Equation 44. VSW(PEAK) = VIN + VOUT + VDIODE

The selected MOSFET should satisfy the condition:

Equation 45. VDS(MAX) > VSW(PEAK)

The peak switch current is given by:

Equation 46. LM3481

Where ΔIL1 and ΔIL2 are the peak-to-peak inductor ripple currents of inductors L1 and L2 respectively.

The rms current through the switch is given by:

Equation 47. LM3481