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

6.3.9 VOUT Programming (VOUT, ATRK, DTRK)

The output voltage VOUT is sensed at the VOUT-pin. Program VOUT between 6V and 60V by I2C, connecting a 10kΩ to 100kΩ resistor at the ATRK/DTRK-pin, applying a voltage between 0.2V and 2V or a digital signal between 8% and 80% duty cycle. The VOUT-bit sets the output voltage in 1V steps or selects the ATRK/DTRK-pin as reference. At startup during the STANDBY state (Functional State Diagram) the ATRK/DTRK-pin programming method analog signal or digital signal is detected. At the transition to the START PHASE 1 and 2 state the ATRK/DTRK-pin programming method is latched and is unchangeable during operation. Allow a DTRK signal to be present for at least three cycles so that it is detected before the programming method is latched. ATRK supports up to 10kHz signals, however, change the ATRK-pin voltage or the DTRK duty cycle slow enough that VOUT is able to follow. In case the ATRK/DTRK-pin set reference voltage is changed faster than the bandwidth of the converter, the inductor current exceeds peak current limit until the slope compensation settles. The inductor peak current overshoot is limited to 90mV CSPx − CSNx sense resistor voltage. The device tries to regulate VOUT as well for ATRK < 0.2V or >2V, but performance is not endured. Enable the 20μA current by CFG setting for VOUT programming by resistor. The 20μA current is sourced through the ATRK-pin and generates the required ATRK voltage for the target VOUT voltage via the external resistor. For analog tracking (ATRK) or digital tracking (DTRK), TI recommends disabling the 20uA current.

Equation for programming VOUT by resistor:

Equation 10. R A T R K =   V O U T 6   V × 10   k Ω

Equation for programming VOUT by voltage (ATRK):

Equation 11. VOUT= VATRK×30

Equation for programming VOUT by digital signal (DTRK):

Equation 12. VOUT= 0.75 V%×Duty Cycle
LM51251A-Q1 VOUT Programming by ResistorFigure 6-16 VOUT Programming by Resistor
LM51251A-Q1 VOUT Tracking by Digital SignalFigure 6-18 VOUT Tracking by Digital Signal
LM51251A-Q1 VOUT Tracking by Analog VoltageFigure 6-17 VOUT Tracking by Analog Voltage