SNVSB29C October   2018  – June 2021 LM5143-Q1


  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Description (continued)
  6. Pin Configuration and Functions
    1. 6.1 Wettable Flanks
  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 Switching Characteristics
    7. 7.7 Typical Characteristics
  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  Enable (EN1, EN2)
      4. 8.3.4  Power Good Monitor (PG1, PG2)
      5. 8.3.5  Switching Frequency (RT)
      6. 8.3.6  Clock Synchronization (DEMB)
      7. 8.3.7  Synchronization Out (SYNCOUT)
      8. 8.3.8  Spread Spectrum Frequency Modulation (DITH)
      9. 8.3.9  Configurable Soft Start (SS1, SS2)
      10. 8.3.10 Output Voltage Setpoint (FB1, FB2)
      11. 8.3.11 Minimum Controllable On-Time
      12. 8.3.12 Error Amplifier and PWM Comparator (FB1, FB2, COMP1, COMP2)
      13. 8.3.13 Slope Compensation
      14. 8.3.14 Inductor Current Sense (CS1, VOUT1, CS2, VOUT2)
        1. Shunt Current Sensing
        2. Inductor DCR Current Sensing
      15. 8.3.15 Hiccup Mode Current Limiting (RES)
      16. 8.3.16 High-Side and Low-Side Gate Drivers (HO1/2, LO1/2, HOL1/2, LOL1/2)
      17. 8.3.17 Output Configurations (MODE, FB2)
        1. Independent Dual-Output Operation
        2. Single-Output Interleaved Operation
        3. Single-Output Multiphase Operation
    4. 8.4 Device Functional Modes
      1. 8.4.1 Standby Modes
      2. 8.4.2 Diode Emulation Mode
      3. 8.4.3 Thermal Shutdown
  9. Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Power Train Components
        1. Buck Inductor
        2. Output Capacitors
        3. Input Capacitors
        4. Power MOSFETs
        5. EMI Filter
      2. 9.1.2 Error Amplifier and Compensation
    2. 9.2 Typical Applications
      1. 9.2.1 Design 1 – High Efficiency, Dual-Output Buck Regulator for Automotive Applications
        1. Design Requirements
        2. Detailed Design Procedure
          1. Custom Design With WEBENCH® Tools
          2. Custom Design With Excel Quickstart Tool
          3. Inductor Calculation
          4. Current-Sense Resistance
          5. Output Capacitors
          6. Input Capacitors
          7. Compensation Components
        3. Application Curves
      2. 9.2.2 Design 2 – Two-Phase, Single-Output Buck Regulator for Automotive ADAS Applications
        1. Design Requirements
        2. Detailed Design Procedures
        3. Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
      1. 11.1.1 Power Stage Layout
      2. 11.1.2 Gate-Drive Layout
      3. 11.1.3 PWM Controller Layout
      4. 11.1.4 Thermal Design and Layout
      5. 11.1.5 Ground Plane Design
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Third-Party Products Disclaimer
      2. 12.1.2 Development Support
      3. 12.1.3 Custom Design With WEBENCH® Tools
    2. 12.2 Documentation Support
      1. 12.2.1 Related Documentation
        1. PCB Layout Resources
        2. Thermal Design Resources
    3. 12.3 Receiving Notification of Documentation Updates
    4. 12.4 Support Resources
    5. 12.5 Trademarks
    6. 12.6 Electrostatic Discharge Caution
    7. 12.7 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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

Power Stage Layout

  1. Input capacitors, output capacitors, and MOSFETs are the constituent components of the power stage of a buck regulator and are typically placed on the top side of the PCB (solder side). The benefits of convective heat transfer are maximized because of leveraging any system-level airflow. In a two-sided PCB layout, small-signal components are typically placed on the bottom side (component side). Insert at least one inner plane, connected to ground, to shield and isolate the small-signal traces from noisy power traces and lines.
  2. The DC/DC regulator has several high-current loops. Minimize the area of these loops in order to suppress generated switching noise and optimize switching performance.
    • Loop 1: The most important loop area to minimize is the path from the input capacitor or capacitors through the high- and low-side MOSFETs, and back to the capacitor or capacitors through the ground connection. Connect the input capacitor or capacitors negative terminal close to the source of the low-side MOSFET (at ground). Similarly, connect the input capacitor or capacitors positive terminal close to the drain of the high-side MOSFET (at VIN). Refer to loop 1 of Figure 11-1.
    • Another loop, not as critical as loop 1, is the path from the low-side MOSFET through the inductor and output capacitor or capacitors, and back to source of the low-side MOSFET through ground. Connect the source of the low-side MOSFET and negative terminal of the output capacitor or capacitors at ground as close as possible.
  3. The PCB trace defined as SW node, which connects to the source of the high-side (control) MOSFET, the drain of the low-side (synchronous) MOSFET and the high-voltage side of the inductor, must be short and wide. However, the SW connection is a source of injected EMI and thus must not be too large.
  4. Follow any layout considerations of the MOSFETs as recommended by the MOSFET manufacturer, including pad geometry and solder paste stencil design.
  5. The SW pin connects to the switch node of the power conversion stage and acts as the return path for the high-side gate driver. The parasitic inductance inherent to loop 1 in Figure 11-1 and the output capacitance (COSS) of both power MOSFETs form a resonant circuit that induces high frequency (greater than 50 MHz) ringing at the SW node. The voltage peak of this ringing, if not controlled, can be significantly higher than the input voltage. Make sure that the peak ringing amplitude does not exceed the absolute maximum rating limit for the SW pin. In many cases, a series resistor and capacitor snubber network connected from the SW node to GND damps the ringing and decreases the peak amplitude. Provide provisions for snubber network components in the PCB layout. If testing reveals that the ringing amplitude at the SW pin is excessive, then include snubber components as needed.