SNVS276I April   2004  – February 2019 LM2743

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Typical Application Diagram
  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  Start Up and Soft-Start
      2. 7.3.2  Normal Operation
      3. 7.3.3  Tracking a Voltage Level
      4. 7.3.4  Tracking Voltage Slew Rate
      5. 7.3.5  Sequencing
      6. 7.3.6  SD Pin Impedance
      7. 7.3.7  MOSFET Gate Drivers
      8. 7.3.8  Power Good Signal
      9. 7.3.9  UVLO
      10. 7.3.10 Current Limit
      11. 7.3.11 Foldback Current Limit
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Synchronous Buck Converter Typical Application using LM2743
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 Custom Design With WEBENCH® Tools
          2. 8.2.1.2.2 Duty Cycle Calculation
          3. 8.2.1.2.3 Input Capacitor
          4. 8.2.1.2.4 Output Inductor
          5. 8.2.1.2.5 Output Capacitor
          6. 8.2.1.2.6 MOSFETs
          7. 8.2.1.2.7 Support Components
          8. 8.2.1.2.8 Control Loop Compensation
          9. 8.2.1.2.9 Efficiency Calculations
        3. 8.2.1.3 Application Curves
      2. 8.2.2 Example Circuit 1
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
        3. 8.2.2.3 Bill of Materials
      3. 8.2.3 Example Circuit 2
        1. 8.2.3.1 Design Requirements
        2. 8.2.3.2 Detailed Design Procedure
        3. 8.2.3.3 Bill of Materials
      4. 8.2.4 Example Circuit 3
        1. 8.2.4.1 Design Requirements
        2. 8.2.4.2 Detailed Design Procedure
        3. 8.2.4.3 Bill of Materials
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Development Support
        1. 11.1.1.1 Custom Design With WEBENCH® Tools
    2. 11.2 Receiving Notification of Documentation Updates
    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

Package Options

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

8.2.1.2.7 Support Components

CIN2 - A small value (0.1-µF to 1-µF) ceramic capacitor should be placed as close as possible to the drain of the high-side MOSFET and source of the low-side MOSFET (dual MOSFETs make this easy). This capacitor should be X5R type dielectric or better.

RCC, CCC- These are standard filter components designed to ensure smooth DC voltage for the chip supply. RCC should be 1 Ω to 10 Ω. CCC should 1 µF, X5R type or better.

CBOOT- Bootstrap capacitor, typically 100 nF.

RPULL-UP – This is a standard pull-up resistor for the open-drain power good signal (PWGD). The recommended value is 10 kΩ connected to VCC. If this feature is not necessary, the resistor can be omitted.

D1 - A small Schottky diode should be used for the bootstrap. It allows for a minimum drop for both high and low-side drivers. The MBR0520 or BAT54 work well in most designs.

RCS - Resistor used to set the current limit. Since the design calls for a peak current magnitude (IOUT+ (0.5 x ΔIOUT)) of 4.8 A, a safe setting would be 6A. (This is below the saturation current of the output inductor, which is 7 A.) Following the equation from the Current Limit section, a 1.3-kΩ resistor should be used.

RFADJ - This resistor is used to set the switching frequency of the chip. The resistor value is calculated from equation in Normal Operation section. For 300-kHz operation, a 97.6-kΩ resistor should be used.

CSS - The soft-start capacitor depends on the user requirements and is calculated based on the equation given in the section titled Start Up and Soft-Start. Therefore, for a 700-μs delay, a 12-nF capacitor is suitable.