SLVSJL6 June   2026 LM851772-Q1

ADVANCE INFORMATION  

  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 Power On Reset and nRST-PIN
      4. 8.3.4  Internal VCC Regulators
        1. 8.3.4.1 VCC1 Regulator
        2. 8.3.4.2 VCC2 Regulator
      5. 8.3.5  Enable and Undervoltage Lockout
        1. 8.3.5.1 UVLO
      6. 8.3.6  Error Amplifier and Control
        1. 8.3.6.1 Output Voltage Regulation
        2. 8.3.6.2 Output Voltage Feedback
        3. 8.3.6.3 Voltage Regulation Loop
        4. 8.3.6.4 Dynamic Voltage Scaling
      7. 8.3.7  Output Voltage Discharge
      8. 8.3.8  Peak Current Sensor
      9. 8.3.9  Short Circuit - Hiccup Protection
      10. 8.3.10 Current Monitor/Limiter
        1. 8.3.10.1 Overview
        2. 8.3.10.2 Output Current Limitation
        3. 8.3.10.3 Output Current Monitor
      11. 8.3.11 Oscillator Frequency Selection
      12. 8.3.12 Frequency Synchronization
      13. 8.3.13 Output Voltage Tracking
        1. 8.3.13.1 Analog Voltage Tracking
        2. 8.3.13.2 Digital Voltage Tracking
      14. 8.3.14 Slope Compensation
      15. 8.3.15 Configurable Soft Start
      16. 8.3.16 Drive Pin
      17. 8.3.17 Dual Random Spread Spectrum – DRSS
      18. 8.3.18 Gate Driver
      19. 8.3.19 Cable Drop Compensation (CDC)
      20. 8.3.20 CFG-Pin and R2D Interface
      21. 8.3.21 Advanced Monitoring Features
        1. 8.3.21.1  Overview
        2. 8.3.21.2  BUSY
        3. 8.3.21.3  OFF
        4. 8.3.21.4  VOUT
        5. 8.3.21.5  IOUT
        6. 8.3.21.6  INPUT
        7. 8.3.21.7  TEMPERATURE
        8. 8.3.21.8  CML
        9. 8.3.21.9  OTHER
        10. 8.3.21.10 ILIM_OP
        11. 8.3.21.11 nFLT/nINT Pin Output
        12. 8.3.21.12 Status Byte
      22. 8.3.22 Protection Features
        1. 8.3.22.1 Thermal Shutdown (TSD)
        2. 8.3.22.2 Overcurrent Protection
        3. 8.3.22.3 Output Overvoltage Protection 1 (OVP1)
        4. 8.3.22.4 Output Overvoltage Protection 2 (OVP2)
        5. 8.3.22.5 Input Voltage Protection (IVP)
        6. 8.3.22.6 Power Good
        7. 8.3.22.7 Boot-Strap Undervoltage Protection
        8. 8.3.22.8 Boot-strap Overvoltage Clamp
        9. 8.3.22.9 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 LM851772-Q1 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 nRST and EN/UVLO Pull-up Resistor Selection
        11. 10.2.2.11 MOSFETs QH1 and QL1
        12. 10.2.2.12 MOSFETs QH2 and QL2
        13. 10.2.2.13 Loop Compensation
        14. 10.2.2.14 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
    1. 13.1 Tape and Reel Information
    2.     132

8.3.10.2 Output Current Limitation

The threshold for the current limit is programmed by the internal DAC. The bandwidth of the current limit control loop is optimized for different loads with a resistor and capacitor network on the ILIMCOMP pin. For resistive loads a simple integrator compensation is selected according the following equations:

Equation 15. CO2=52×π×fbw×R(LOAD)

Where CO2 is the capacitance after the average current sense resistor R(SNS)

fbw is the bandwidth of the voltage loop compensation (see Voltage Regulation Loop)

Equation 16. CO1 =CO - CO2 

Where CO is the total output capacitance determined by the voltage loop calculation and the applications voltage ripple requirement.

Where CO1 is the capacitance before the average current sense resistor R(SNS)

Equation 17. fp=12×π×R(SNS)×CO2
Equation 18. fbwilim=fp×10-0.25
Equation 19. C(ILIMCOMP)=gm(ILIMCOMP)2π×fbwilim
LM851772-Q1 Simplified Schematic Current Limit Components With Resistive Load Figure 8-18 Simplified Schematic Current Limit Components With Resistive Load

For an electronic load (CC-mode CR-mode) a type II compensation network is necessary in most cases. To adopt to the internal regulation loop and bandwidth of the used electronic load. Please refer to the Quick Start Calculator Tool for more detailed optimization.

The read-out register value of the ''ILIM_THRESHOLD" control register is clamped for the lower and for the upper limit of the register range.

  • The reg. readout value is clamped to the lowest clamp current (for example 500mA) if a register value below the value of clamp current been written in before.
  • The reg. readout value is clamped to the highest clamp current if a register value above the highest value of clamp current has been written in before.