SNVS686L March   2011  – June 2025 LMZ22005

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    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 Synchronization Input
      2. 6.3.2 Output Overvoltage Protection
      3. 6.3.3 Current Limit
      4. 6.3.4 Thermal Protection
      5. 6.3.5 Prebiased Start-Up
    4. 6.4 Device Functional Modes
      1. 6.4.1 Discontinuous And Continuous Conduction Modes
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
        1. 7.2.2.1 Custom Design With WEBENCH® Tools
        2. 7.2.2.2 Design Steps
        3. 7.2.2.3 Enable Divider, RENT, RENB, and RENH Selection
        4. 7.2.2.4 Output Voltage Selection
        5. 7.2.2.5 Soft-start Capacitor Selection
        6. 7.2.2.6 Tracking Supply Divider Option
        7. 7.2.2.7 CO Selection
        8. 7.2.2.8 CIN Selection
        9. 7.2.2.9 Discontinuous and Continuous Conduction Modes Selection
      3. 7.2.3 Application Curves
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Examples
      3. 7.4.3 Power Dissipation and Thermal Considerations
      4. 7.4.4 Power Module SMT Guidelines
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Development Support
        1. 8.1.1.1 Custom Design With WEBENCH® Tools
    2. 8.2 Documentation Support
      1. 8.2.1 Related Documentation
    3. 8.3 Receiving Notification of Documentation Updates
    4. 8.4 Support Resources
    5. 8.5 Trademarks
    6. 8.6 Electrostatic Discharge Caution
    7. 8.7 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

7.2.2.8 CIN Selection

The LMZ22005 module contains only a small amount of input capacitance. Additional input capacitance is required external to the module to handle the input ripple current of the application. The input capacitor can be several capacitors in parallel. This input capacitance must be located in very close proximity to the module. Input capacitor selection is generally directed to satisfy the input ripple current requirements rather than by capacitance value. Input ripple current rating is dictated by the equation:

Equation 10. I(CIN(RMS)) ≊ 1 / 2 × IO × SQRT (D / 1 – D)

where

  • D ≊ VO / VIN

As a point of reference, the worst case ripple current occurs when the module is presented with full load current and when VIN = 2 × VO.

Recommended minimum input capacitance is 22-µF X7R (or X5R) ceramic with a voltage rating at least 25% higher than the maximum applied input voltage for the application. TI recommends to pay attention to the voltage and temperature derating of the capacitor selected. The ripple current rating of ceramic capacitors can be missing from the capacitor data sheet and you can have to contact the capacitor manufacturer for this parameter.

If the system design requires a certain minimum value of peak-to-peak input ripple voltage (ΔVIN) be maintained then the following equation can be used.

Equation 11. CIN ≥ IO × D × (1 – D) / fSW-CCM × ΔVIN

If ΔVIN is 1% of VIN for a 12-V input to 3.3-V output application this equals 120 mV and fSW = 812 kHz.

Equation 12. CIN ≥ 5 A × 3.3 V / 12 V × (1 – 3.3 V / 12 V) / (812000 × 0.120 V) ≥ 10.2 μF

Additional bulk capacitance with higher ESR can be required to damp any resonant effects of the input capacitance and parasitic inductance of the incoming supply lines. The LMZ22005 typical applications schematic recommends a 150-μF 50-V aluminum capacitor for this function. There are many situations where this capacitor is not necessary.