SLVSH49 October   2024 TPSM82916

ADVANCE INFORMATION  

  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  Smart Config (S-CONF)
      2. 6.3.2  Device Enable (EN/SYNC)
      3. 6.3.3  Device Synchronization (EN/SYNC)
      4. 6.3.4  Spread Spectrum Modulation
      5. 6.3.5  Output Discharge
      6. 6.3.6  Undervoltage Lockout (UVLO)
      7. 6.3.7  Power-Good Output
      8. 6.3.8  Noise Reduction and Soft-Start Capacitor (NR/SS)
      9. 6.3.9  Current Limit and Short-Circuit Protection
      10. 6.3.10 Thermal Shutdown
    4. 6.4 Device Functional Modes
      1. 6.4.1 Fixed Frequency Pulse Width Modulation
      2. 6.4.2 Low Duty Cycle Operation
      3. 6.4.3 High Duty Cycle Operation (100% Duty Cycle)
      4. 6.4.4 Second Stage L-C Filter Compensation (Optional)
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Applications
      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 External Component Selection
          1. 7.2.2.2.1 Switching Frequency Selection
          2. 7.2.2.2.2 Output Capacitor Selection
          3. 7.2.2.2.3 Ferrite Bead Selection for Second L-C Filter
          4. 7.2.2.2.4 Input Capacitor Selection
          5. 7.2.2.2.5 Setting the Output Voltage
          6. 7.2.2.2.6 NR/SS Capacitor Selection
    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 Device Support
      1. 8.1.1 Third-Party Products Disclaimer
      2. 8.1.2 Development Support
        1. 8.1.2.1 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

Package Options

Mechanical Data (Package|Pins)
  • VCE|16
Thermal pad, mechanical data (Package|Pins)
Orderable Information
7.2.2.2.3 Ferrite Bead Selection for Second L-C Filter

Using a ferrite bead for the second stage L-C filter minimizes the external component count because most of the noise sensitive circuits use a RF bead for high frequency attenuation as a default component at the inputs.

Make sure to select a ferrite bead with sufficiently high inductance at full load, and with low DC resistance (below 10mΩ) to keep the module efficiency as high as possible. The ferrite bead inductance decreases with increased load current. Therefore, the ferrite bead must have a current rating much higher than the desired load current.

The recommendation is to choose a ferrite bead with an impedance of 8Ω to 20Ω at 100MHz. Ferrite beads can be used in parallel if higher current is needed, however this can halve the inductance and filtering. Refer to Table 7-5 for possible ferrite beads.

Table 7-5 Recommended Ferrite Beads
PART NUMBER MANUFACTURER SIZE IMPEDANCE AT 100MHZ INDUCTANCE AT 100MHz (CALCULATED) DC RESISTANCE CURRENT RATING
BLE18PS080SN1 MuRata 0603 8.5Ω 13.5 nH 4mΩ 5A
BLE32SN120SN1L MuRata 1210 12Ω 18 nH 0.78mΩ 20A
74279221100 Wurth Elektronik 1206 10Ω 15.9 nH 3mΩ 10.5A
7427922808 Wurth Electronik 0603 8Ω 12.7 nH 5mΩ 9.5A

The internal compensation has been designed to be stable with up to 50nH of inductance in the second stage filter. To achieve low ripple, the second L-C filter requires only 5nH to 10nH inductance. The inductance can be estimated from the ferrite bead impedance specification at 100MHz, with the assumption that the inductance is similar at the selected module switching frequency of 1MHz, 1.4MHz, or 2.2MHz, and can be verified through tools available on some manufacturer websites. Use Equation 5 to calculate the inductance of a ferrite bead:

Equation 5. L = Ζ 2 π   × f

where

  • Z is the impedance of the ferrite bead in ohms at the specified frequency (usually 100MHz).
  • f is the specified frequency (usually 100MHz).