SNVSC77 December   2024 LM5125-Q1

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 Timing Requirements
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1  Device Configuration (CFG0-pin, CFG1-pin, CFG2-pin)
      2. 6.3.2  Switching Frequency and Synchronization (SYNCIN)
      3. 6.3.3  Dual Random Spread Spectrum (DRSS)
      4. 6.3.4  Operation Modes (BYPASS, DEM, FPWM)
      5. 6.3.5  Dual- and Multi-phase Operation
      6. 6.3.6  BIAS (BIAS-pin)
      7. 6.3.7  Soft Start (SS-pin)
      8. 6.3.8  VOUT Programming (VOUT, ATRK, DTRK)
      9. 6.3.9  Protections
      10. 6.3.10 VOUT Overvoltage Protection (OVP)
      11. 6.3.11 Thermal Shutdown (TSD)
      12. 6.3.12 Power-Good Indicator (PGOOD-pin)
      13. 6.3.13 Current Sensing, Peak Current Limit, and Slope Compensation (CSP1, CSP2, CSN1, CSN2)
      14. 6.3.14 Current Sense Programming (CSP1, CSP2, CSN1, CSN2)
      15. 6.3.15 Input Current Limit and Monitoring (ILIM, IMON, DLY)
      16. 6.3.16 Signal Deglitch Overview
      17. 6.3.17 MOSFET Drivers, Integrated Boot Diode, and Hiccup Mode Fault Protection (LOx, HOx, HBx-pin)
    4. 6.4 Device Functional Modes
      1. 6.4.1 Shutdown State
  8. 7 Application and Implementation
    1. 7.1 Application Information
      1. 7.1.1 Feedback Compensation
    2. 7.2 Typical Application
      1. 7.2.1 Application
      2. 7.2.2 Design Requirements
      3. 7.2.3 Detailed Design Procedure
        1. 7.2.3.1  Determine the Total Phase Number
        2. 7.2.3.2  Determining the Duty Cycle
        3. 7.2.3.3  Timing Resistor RT
        4. 7.2.3.4  Inductor Selection Lm
        5. 7.2.3.5  Current Sense Resistor Rcs
        6. 7.2.3.6  Current Sense Filter RCSFP, RCSFN, CCS
        7. 7.2.3.7  Low-Side Power Switch QL
        8. 7.2.3.8  High-Side Power Switch QH and Additional Parallel Schottky Diode
        9. 7.2.3.9  Snubber Components
        10. 7.2.3.10 Vout Programming
        11. 7.2.3.11 Input Current Limit (ILIM/IMON)
        12. 7.2.3.12 UVLO Divider
        13. 7.2.3.13 Soft Start
        14. 7.2.3.14 CFG Settings
        15. 7.2.3.15 Output Capacitor Cout
        16. 7.2.3.16 Input Capacitor Cin
        17. 7.2.3.17 Bootstrap Capacitor
        18. 7.2.3.18 VCC Capacitor CVCC
        19. 7.2.3.19 BIAS Capacitor
        20. 7.2.3.20 VOUT Capacitor
        21. 7.2.3.21 Loop Compensation
      4. 7.2.4 Application Curves
        1. 7.2.4.1 Efficiency
        2. 7.2.4.2 Steady State Waveforms
        3. 7.2.4.3 Step Load Response
        4. 7.2.4.4 Sync Operation
        5. 7.2.4.5 Thermal Performance
    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 Related Documentation
    2. 8.2 Receiving Notification of Documentation Updates
    3. 8.3 Support Resources
    4. 8.4 Trademarks
    5. 8.5 Electrostatic Discharge Caution
    6. 8.6 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information
    1. 10.1 Tape and Reel Information
    2.     85

Package Options

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

7.2.3.16 Input Capacitor Cin

Input capacitors are always required to provide a stable input voltage. The input capacitors must be able to handle the inductor ripple current.

The single phase boost input RMS ripple current can be expressed as:

Equation 63. Iin_1p_rms=Ipp12

The input RMS current is reduced with interleaving as shown in Figure 7-10. Dual phase interleaved boost input RMS ripple current can be expressed as:

Equation 64. Iin_2p_rms=Ipp12×1-2DD',  D<0.5Ipp12×2D-1D,  D≥0.5
LM5125-Q1 Normalized Output Capacitor RMS Ripple Current Figure 7-10 Normalized Output Capacitor RMS Ripple Current

The input capacitor is also an important part of the input filter. Higher capacitance and ESR help damping the input filter better. Aluminum electrolytic capacitor is a good choice for input capacitor with high capacitance and ESR. Refer to Input Filter Design for Switching Power Supplies application note for more details.