SLVSHB3 November   2025 LM51251A-Q1

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Timing Requirements
    7. 5.7 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1  Device Configuration (CFG-pin)
      2. 6.3.2  Device and Phase Enable/Disable (UVLO/EN, EN2)
      3. 6.3.3  Dual Device Operation
      4. 6.3.4  Switching Frequency and Synchronization (SYNCIN)
      5. 6.3.5  Dual Random Spread Spectrum (DRSS)
      6. 6.3.6  Operation Modes (BYPASS, DEM, FPWM)
      7. 6.3.7  VCC Regulator, BIAS (BIAS-pin, VCC-pin)
      8. 6.3.8  Soft Start (SS-pin)
      9. 6.3.9  VOUT Programming (VOUT, ATRK, DTRK)
      10. 6.3.10 Protections
        1. 6.3.10.1 VOUT Overvoltage Protection (OVP)
        2. 6.3.10.2 Thermal Shutdown (TSD)
      11. 6.3.11 Fault Indicator (nFAULT-pin)
      12. 6.3.12 Slope Compensation (CSP1, CSP2, CSN1, CSN2)
      13. 6.3.13 Current Sense Setting and Switch Peak Current Limit (CSP1, CSP2, CSN1, CSN2)
      14. 6.3.14 Input Current Limit and Monitoring (ILIM, IMON, DLY)
      15. 6.3.15 Maximum Duty Cycle and Minimum Controllable On-time Limits
      16. 6.3.16 Signal Deglitch Overview
      17. 6.3.17 MOSFET Drivers, Integrated Boot Diode, and Hiccup Mode Fault Protection (LOx, HOx, HBx-pin)
      18. 6.3.18 I2C Features
        1. 6.3.18.1 Register VOUT (0x0)
        2. 6.3.18.2 Register Configuration 1 (0x1)
        3. 6.3.18.3 Register Configuration 2 (0x2)
        4. 6.3.18.4 Register Configuration 3 (0x3)
        5. 6.3.18.5 Register Operation State (0x4)
        6. 6.3.18.6 Register Status Byte (0x5)
        7. 6.3.18.7 Register Clear Faults (0x6)
    4. 6.4 Device Functional Modes
      1. 6.4.1 Shutdown State
    5. 6.5 Programming
      1. 6.5.1 I2C Bus Operation
  8. 7 LM51251A-Q1 Registers
  9. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Feedback Compensation
      2. 8.1.2 Non-synchronous Application
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1  Determine the Total Phase Number
        2. 8.2.2.2  Determining the Duty Cycle
        3. 8.2.2.3  Timing Resistor RT
        4. 8.2.2.4  Inductor Selection Lm
        5. 8.2.2.5  Current Sense Resistor Rcs
        6. 8.2.2.6  Current Sense Filter RCSFP, RCSFN, CCS
        7. 8.2.2.7  Low-Side Power Switch QL
        8. 8.2.2.8  High-Side Power Switch QH
        9. 8.2.2.9  Snubber Components
        10. 8.2.2.10 Vout Programming
        11. 8.2.2.11 Input Current Limit (ILIM/IMON)
        12. 8.2.2.12 UVLO Divider
        13. 8.2.2.13 Soft Start
        14. 8.2.2.14 CFG Settings
        15. 8.2.2.15 Output Capacitor Cout
        16. 8.2.2.16 Input Capacitor Cin
        17. 8.2.2.17 Bootstrap Capacitor
        18. 8.2.2.18 VCC Capacitor CVCC
        19. 8.2.2.19 BIAS Capacitor
        20. 8.2.2.20 VOUT Capacitor
        21. 8.2.2.21 Loop Compensation
      3. 8.2.3 Application Curves
        1. 8.2.3.1 Efficiency
        2. 8.2.3.2 Steady State Waveforms
        3. 8.2.3.3 Step Load Response
        4. 8.2.3.4 Sync Operation
        5. 8.2.3.5 AC Loop Response Curve
        6. 8.2.3.6 Thermal Performance
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Documentation Support
      1. 9.1.1 Related Documentation
    2. 9.2 Receiving Notification of Documentation Updates
    3. 9.3 Support Resources
    4. 9.4 Trademarks
    5. 9.5 Electrostatic Discharge Caution
    6. 9.6 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

3 Description

The LM51251A-Q1 is a stackable, dual-phase, synchronous boost controller with I2C interface. The device provides a regulated output voltage for lower or equal input voltage also supporting VI to VOUT bypass mode to save power. Stack two devices with or without external clock.

Dynamically program VOUT using the analog or digital ATRK/DTRK function or I2C programming. VI is supported down to 2.5V after start-up as the internal VCC supply is automatically switched from VBIAS to VOUT for VBIAS < 4.5V. The fixed switching frequency is set between 100kHz and 2.2MHz through a resistor on the RT pin or the SYNCIN clock. The switching modes FPWM or diode emulation can be changed during operation.

The implemented protections peak current limit, average input current limit, average inductor current monitor, over and undervoltage protection, and the thermal shutdown protect the device and the application.

Package Information
PART NUMBER PACKAGE(1) PACKAGE SIZE(2)
LM51251A-Q1 RHB (VQFN, 32) 5mm x 5mm
(1) For more information, see Section 11.
(2) The package size (length × width) is a nominal value and includes pins, where applicable.
LM51251A-Q1 Typical Application Typical Application