SNVSBV6B December   2020  – January 2023 LM25149-Q1

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Description (continued)
  6. 6 Pin Configuration and Functions
    1. 6.1 Wettable Flanks
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings 
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Active EMI Filter
    7. 7.7 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Input Voltage Range (VIN)
      2. 8.3.2  High-Voltage Bias Supply Regulator (VCC, VCCX, VDDA)
      3. 8.3.3  Precision Enable (EN)
      4. 8.3.4  Power-Good Monitor (PG)
      5. 8.3.5  Switching Frequency (RT)
      6. 8.3.6  Active EMI Filter
      7. 8.3.7  Dual Random Spread Spectrum (DRSS)
      8. 8.3.8  Soft Start
      9. 8.3.9  Output Voltage Setpoint (FB)
      10. 8.3.10 Minimum Controllable On Time
      11. 8.3.11 Error Amplifier and PWM Comparator (FB, EXTCOMP)
      12. 8.3.12 Slope Compensation
      13. 8.3.13 Inductor Current Sense (ISNS+, VOUT)
        1. 8.3.13.1 Shunt Current Sensing
        2. 8.3.13.2 Inductor DCR Current Sensing
      14. 8.3.14 Hiccup Mode Current Limiting
      15. 8.3.15 High-Side and Low-Side Gate Drivers (HO, LO)
      16. 8.3.16 Output Configurations (CNFG)
      17. 8.3.17 Single-Output Dual-Phase Operation
    4. 8.4 Device Functional Modes
      1. 8.4.1 Sleep Mode
      2. 8.4.2 Pulse Frequency Modulation and Synchronization (PFM/SYNC)
      3. 8.4.3 Thermal Shutdown
  9. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Power Train Components
        1. 9.1.1.1 Buck Inductor
        2. 9.1.1.2 Output Capacitors
        3. 9.1.1.3 Input Capacitors
        4. 9.1.1.4 Power MOSFETs
        5. 9.1.1.5 EMI Filter
        6. 9.1.1.6 Active EMI Filter
      2. 9.1.2 Error Amplifier and Compensation
    2. 9.2 Typical Applications
      1. 9.2.1 Design 1 – High-Efficiency 2.1-MHz Synchronous Buck Regulator
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
          1. 9.2.1.2.1  Custom Design With WEBENCH® Tools
          2. 9.2.1.2.2  Custom Design With Excel Quickstart Tool
          3. 9.2.1.2.3  Buck Inductor
          4. 9.2.1.2.4  Current-Sense Resistance
          5. 9.2.1.2.5  Output Capacitors
          6. 9.2.1.2.6  Input Capacitors
          7. 9.2.1.2.7  Frequency Set Resistor
          8. 9.2.1.2.8  Feedback Resistors
          9. 9.2.1.2.9  Compensation Components
          10. 9.2.1.2.10 Active EMI Components
        3. 9.2.1.3 Application Curves
      2. 9.2.2 Design 2 – High Efficiency 440-kHz Synchronous Buck Regulator
        1. 9.2.2.1 Design Requirements
        2. 9.2.2.2 Detailed Design Procedure
        3. 9.2.2.3 Application Curves
      3. 9.2.3 Design 3 – Dual-Phase 400-kHz 20-A Synchronous Buck Regulator
        1. 9.2.3.1 Design Requirements
        2. 9.2.3.2 Detailed Design Procedure
        3. 9.2.3.3 Application Curves
    3. 9.3 Power Supply Recommendations
    4. 9.4 Layout
      1. 9.4.1 Layout Guidelines
        1. 9.4.1.1 Power Stage Layout
        2. 9.4.1.2 Gate-Drive Layout
        3. 9.4.1.3 PWM Controller Layout
        4. 9.4.1.4 Active EMI Layout
        5. 9.4.1.5 Thermal Design and Layout
        6. 9.4.1.6 Ground Plane Design
      2. 9.4.2 Layout Example
  10. 10Device and Documentation Support
    1. 10.1 Device Support
      1. 10.1.1 Development Support
        1. 10.1.1.1 Custom Design With WEBENCH® Tools
    2. 10.2 Documentation Support
      1. 10.2.1 Related Documentation
        1. 10.2.1.1 PCB Layout Resources
        2. 10.2.1.2 Thermal Design Resources
    3. 10.3 Receiving Notification of Documentation Updates
    4. 10.4 Support Resources
    5. 10.5 Trademarks
    6. 10.6 Electrostatic Discharge Caution
    7. 10.7 Glossary
  11. 11Mechanical, Packaging, and Orderable Information

Package Options

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

9.1.1.6 Active EMI Filter

Active EMI filtering uses a capacitive multiplier to reduce the magnitude of the LC filtering components. Extra compensation components are needed, but the reduction in LC size outweigh the required network. The active EMI filter design steps are as follows:

  • Calculate the required attenuation of the EMI filter at the switching frequency, similar to the passive EMI filter.
  • Select input filter inductor LIN between 0.47 µH and 4.7 µH, lower than the passive EMI inductor.
  • Use recommended values for sensing and compensation components CSEN, CAEFC, RAEFC, CINC, and RINC.
  • Calculate active EMI injection capacitor CINJ.
  • Calculate active EMI damping resistor RDAMP.
  • For low-frequency designs (FSW < 1 MHz), calculate the active EMI damping capacitance CDAMP.
    Figure 9-3 Active EMI Filter for a Buck Regulator

Note: TI does not recommending placing a capacitor from VIN-EMI to GND. However, if a capacitor from VIN-EMI to GND is required, ensure a capacitor with greater than 100 mΩ of ESR is used. Capacitors with less than 100 mΩ of ESR, such as ceramics, can cause the active EMI filter to become unstable.

The active EMI filter is intended to cancel differential-mode noise in steady-state conditions. Large pertubations or low-frequency transients on the VIN-EMI node can potentially limit the amplifier noise canceling ability.

Use Equation 21 to determine the attenuation required. Table 9-2 lists the recommended compensation and sensing component values. Use low FSW component values if FSW ≤ 1 MHz and high FSW component values if FSW > 1MHz.

Table 9-2 Recommended Active EMI Compensation Component Values
AEF COMPONENTLOW FSWHIGH FSWDESCRIPTION
CSEN0.1 µF0.1 µFSensing capacitor
RAEFC1 kΩ200 ΩCompensation
CAEFC1 nF5 nFCompensation
RINC0.47 Ω0.47 ΩCompensation
CINC0.1 µF0.1 µFCompensation
RAEFVDD 3 Ω 3 Ω Decoupling
CAEFVDD 2.2 µF 2.2 µF Decoupling

Select the desired LIN. Determine the Active EMI filter capacitance CINJ from Equation 26.

Equation 26. GUID-986FAD8C-5827-4F2B-9F20-7CD68C54ACC7-low.gif

Determine the Active EMI damping resistor RDAMP from Equation 27.

Equation 27. GUID-665E5863-18BC-45E6-88E5-487DBD6C7843-low.gif

Determine the Active EMI damping capacitance CDAMP from Equation 28. CDAMP is not needed for FSW > 1 MHz.

Equation 28. GUID-434A2831-EAE1-44B4-926E-E128C58C82F9-low.gif