SNVS710I March   2011  – December 2015 LMZ13608

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Application Schematic
      2.      Efficiency 3.3-V Output at 25°C
  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 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 Output Overvoltage Protection
      2. 7.3.2 Current Limit
      3. 7.3.3 Thermal Protection
      4. 7.3.4 Prebiased Start-Up
    4. 7.4 Device Functional Modes
      1. 7.4.1 Discontinuous Conduction and Continuous Conduction Modes
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Design Steps
        2. 8.2.2.2 Enable Divider, RENT, RENB and RENH Selection
        3. 8.2.2.3 Output Voltage Selection
        4. 8.2.2.4 Soft-Start Capacitor Selection
        5. 8.2.2.5 Tracking Supply Divider Option
        6. 8.2.2.6 COUT Selection
        7. 8.2.2.7 CIN Selection
        8. 8.2.2.8 Discontinuous Conduction and Continuous Conduction Modes Selection
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Examples
    3. 10.3 Power Dissipation and Thermal Considerations
    4. 10.4 Power Module SMT Guidelines
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
      2. 11.1.2 Development Support
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Community Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information
    1. 12.1 Tape and Reel Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8.2.2.7 CIN Selection

The LMZ13608 module contains two internal ceramic input capacitors. 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. LMZ13608 30151492.gif

where

  • D ≊ VOUT / VIN

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

Recommended minimum input capacitance is 30-µF X7R (or X5R) ceramic with a voltage rating at least 25% higher than the maximum applied input voltage for the application. TI also recommends to pay attnetion to the voltage and temperature derating of the capacitor selected.

NOTE

Ripple current rating of ceramic capacitors may be missing from the capacitor data sheet and you may 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) to be maintained then the following equation may be used.

Equation 11. LMZ13608 30151493.gif

If ΔVIN is 200 mV or 1.66% of VIN for a 12-V input to 3.3-V output application and fSW = 350 kHz then:

Equation 12. LMZ13608 30151494.gif

Additional bulk capacitance with higher ESR may be required to damp any resonant effects of the input capacitance and parasitic inductance of the incoming supply lines. The LMZ13608 typical applications schematic and evaluation board include a 150-μF 50-V aluminum capacitor for this function. There are many situations where this capacitor is not necessary.