SNVSD07 October   2025 LM251772-Q1

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison
  6. 5 Pin Configuration and Functions
  7. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 Handling Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Timing Requirements
    7. 6.7 Typical Characteristics
  8. 7 Parameter Measurement Information
  9. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Buck-Boost Control Scheme
        1. 8.3.1.1 Buck Mode
        2. 8.3.1.2 Boost Mode
        3. 8.3.1.3 Buck-Boost Mode
      2. 8.3.2  Power Save Mode
      3. 8.3.3  Reference System
        1. 8.3.3.1 VIO LDO and nRST-PIN
      4. 8.3.4  Supply Voltage Selection – VSMART Switch and Selection Logic
      5. 8.3.5  Enable and Undervoltage Lockout
        1. 8.3.5.1 UVLO
      6. 8.3.6  Internal VCC Regulators
        1. 8.3.6.1 VCC1 Regulator
        2. 8.3.6.2 VCC2 Regulator
      7. 8.3.7  Error Amplifier and Control
        1. 8.3.7.1 Output Voltage Regulation
        2. 8.3.7.2 Output Voltage Feedback
        3. 8.3.7.3 Voltage Regulation Loop
        4. 8.3.7.4 Dynamic Voltage Scaling
      8. 8.3.8  Output Voltage Discharge
      9. 8.3.9  Peak Current Sensor
      10. 8.3.10 Short Circuit - Hiccup Protection
      11. 8.3.11 Current Monitor/Limiter
        1. 8.3.11.1 Overview
        2. 8.3.11.2 Output Current Limitation
        3. 8.3.11.3 Output Current Monitor
      12. 8.3.12 Oscillator Frequency Selection
      13. 8.3.13 Frequency Synchronization
      14. 8.3.14 Output Voltage Tracking
        1. 8.3.14.1 Analog Voltage Tracking
        2. 8.3.14.2 Digital Voltage Tracking
      15. 8.3.15 Slope Compensation
      16. 8.3.16 Configurable Soft Start
      17. 8.3.17 Drive Pin
      18. 8.3.18 Dual Random Spread Spectrum – DRSS
      19. 8.3.19 Gate Driver
      20. 8.3.20 Cable Drop Compensation (CDC)
      21. 8.3.21 CFG-pin and R2D Interface
      22. 8.3.22 Advanced Monitoring Features
        1. 8.3.22.1  Overview
        2. 8.3.22.2  BUSY
        3. 8.3.22.3  OFF
        4. 8.3.22.4  VOUT
        5. 8.3.22.5  IOUT
        6. 8.3.22.6  INPUT
        7. 8.3.22.7  TEMPERATURE
        8. 8.3.22.8  CML
        9. 8.3.22.9  OTHER
        10. 8.3.22.10 ILIM_OP
        11. 8.3.22.11 nFLT/nINT Pin Output
        12. 8.3.22.12 Status Byte
      23. 8.3.23 Protection Features
        1. 8.3.23.1  Thermal Shutdown (TSD)
        2. 8.3.23.2  Over Current Protection
        3. 8.3.23.3  Output Over Voltage Protection 1 (OVP1)
        4. 8.3.23.4  Output Over Voltage Protection 2 (OVP2)
        5. 8.3.23.5  Input Voltage Protection (IVP)
        6. 8.3.23.6  Input Voltage Regulation (IVR)
        7. 8.3.23.7  Power Good
        8. 8.3.23.8  Boot-Strap Under Voltage Protection
        9. 8.3.23.9  Boot-strap Over Voltage Clamp
        10. 8.3.23.10 CRC - CHECK
    4. 8.4 Device Functional Modes
      1. 8.4.1 Overview
      2. 8.4.2 Logic State Description
    5. 8.5 Programming
      1. 8.5.1 I2C Bus Operation
      2. 8.5.2 Clock Stretching
      3. 8.5.3 Data Transfer Formats
      4. 8.5.4 Single READ From a Defined Register Address
      5. 8.5.5 Sequential READ Starting from a Defined Register Address
      6. 8.5.6 Single WRITE to a Defined Register Address
      7. 8.5.7 Sequential WRITE Starting at a Defined Register Address
  10. 9 LM251772 Registers
  11. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
        1. 10.2.2.1  Custom Design with WEBENCH Tools
        2. 10.2.2.2  Frequency
        3. 10.2.2.3  Feedback Divider
        4. 10.2.2.4  Inductor and Current Sense Resistor Selection
        5. 10.2.2.5  Output Capacitor
        6. 10.2.2.6  Input Capacitor
        7. 10.2.2.7  Slope Compensation
        8. 10.2.2.8  UVLO Divider
        9. 10.2.2.9  Soft-Start Capacitor
        10. 10.2.2.10 MOSFETs QH1 and QL1
        11. 10.2.2.11 MOSFETs QH2 and QL2
        12. 10.2.2.12 Loop Compensation
        13. 10.2.2.13 External Component Selection
      3. 10.2.3 Application Curves
    3. 10.3 USB-PD Source with Power Path
    4. 10.4 Parallel (Multiphase) Operation
    5. 10.5 Wireless Charging Supply
    6. 10.6 Power Supply Recommendations
    7. 10.7 Layout
      1. 10.7.1 Layout Guidelines
        1. 10.7.1.1 Power Stage Layout
        2. 10.7.1.2 Gate Driver Layout
        3. 10.7.1.3 Controller Layout
      2. 10.7.2 Layout Example
  12. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Support Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  13. 12Revision History
  14. 13Mechanical, Packaging, and Orderable Information

10.2.2.6 Input Capacitor

In buck mode, the input capacitor supplies high ripple current. The RMS current in the input capacitor is given by:

Equation 39. ICIN(RMS)= IOUT× D×(1-D)

The maximum RMS current occurs at D = 0.5, which gives ICIN(RMS) = IOUT / 2 = 2.5A. A combination of ceramic and bulk capacitors provides a short path for high di/dt current and to reduces the output voltage ripple. Figure 10-1 is a good starting point for CIN for typical applications.