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
7.2.1.2.8 Output Capacitor Selection

The output capacitor in a boost converter provides all the output current when the inductor is charging. As a result it sees very large ripple currents. The output capacitor should be capable of handling the maximum rms current. The rms current in the output capacitor is:

Equation 41. LM3481

Where

Equation 42. LM3481

and D, the duty cycle is equal to (VOUT − VIN)/VOUT.

The ESR and ESL of the output capacitor directly control the output ripple. Use capacitors with low ESR and ESL at the output for high efficiency and low ripple voltage. Surface mount tantalums, surface mount polymer electrolytic and polymer tantalum, Sanyo- OSCON, or multi-layer ceramic capacitors are recommended at the output.