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

8.2.2.6 COUT Selection

None of the required COUT output capacitance is contained within the module. A minimum value ranging from 330 μF for 6-VOUT to 660 μF for 1.2-VOUT applications is required based on the values of internal compensation in the error amplifier. These minimum values can be decreased if the effective capacitor ESR is higher than 15 mΩ.

A Low ESR (15 mΩ) tantalum, organic semiconductor or specialty polymer capacitor types in parallel with a 47-nF X7R ceramic capacitor for high-frequency noise reduction is recommended for obtaining lowest ripple. The output capacitor COUT may consist of several capacitors in parallel placed in close proximity to the module. The output voltage ripple of the module depends on the equivalent series resistance (ESR) of the capacitor bank, and can be calculated by multiplying the ripple current of the module by the effective impedance of your chosen output capacitors (for ripple current calculation, see Equation 14). Electrolytic capacitors will have large ESR and lead to larger output ripple than ceramic or polymer types. For this reason a combination of ceramic and polymer capacitors is recommended for low output ripple performance.

The output capacitor assembly must also meet the worst case ripple current rating of ΔiL, as calculated in Equation 14 below. Loop response verification is also valuable to confirm closed loop behavior.

For applications with dynamic load steps; the following equation provides a good first pass approximation of COUT for load transient requirements.

Equation 8. LMZ13608 30151490.gif

For 12 VIN, 3.3 VOUT, a transient voltage of 5% of VOUT = 0.165 V (ΔVOUT), a 7A load step (ISTEP), an output capacitor effective ESR of 3 mΩ, and a switching frequency of 350 kHz (fSW):

Equation 9. LMZ13608 30151491.gif

NOTE

The stability requirement for minimum output capacitance must always be met.

One recommended output capacitor combination is two 330-μF, 15-mΩ ESR tantalum polymer capacitors connected in parallel with a 47-µF 6.3-V X5R ceramic. This combination provides excellent performance that may exceed the requirements of certain applications. Additionally some small 47-nF ceramic capacitors can be used for high-frequency EMI suppression.