SNVSCU4 October   2025 LM25137

PRODMIX  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Related Products
  6. 5 Pin Configuration and Functions
    1. 5.1 Wettable Flanks
  7. 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
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Input Voltage Range (VIN)
      2. 7.3.2  Bias Supply Regulator (VCC, BIAS1/VOUT1, VDDA)
      3. 7.3.3  Precision Enable (EN1, EN2)
      4. 7.3.4  Switching Frequency (RT)
      5. 7.3.5  Pulse Frequency Modulation and Synchronization (PFM/SYNC)
      6. 7.3.6  Synchronization Out (SYNCOUT)
      7. 7.3.7  Dual Random Spread Spectrum (DRSS)
      8. 7.3.8  Configurable Soft Start (RSS)
      9. 7.3.9  Output Voltage Setpoints (FB1, FB2)
      10. 7.3.10 Error Amplifier and PWM Comparator (FB1, FB2, COMP1, COMP2)
        1. 7.3.10.1 Slope Compensation
      11. 7.3.11 Inductor Current Sense (ISNS1+, BIAS1/VOUT1, ISNS2+, VOUT2)
        1. 7.3.11.1 Shunt Current Sensing
        2. 7.3.11.2 Inductor DCR Current Sensing
      12. 7.3.12 Minimum Controllable On-Time
      13. 7.3.13 100% Duty Cycle Capability
      14. 7.3.14 MOSFET Gate Drivers (HO1, HO2, LO1, LO2)
      15. 7.3.15 Output Configurations (CNFG)
        1. 7.3.15.1 Independent Dual-Output Operation
        2. 7.3.15.2 Single-Output Interleaved Operation
        3. 7.3.15.3 Single-Output Multiphase Operation
    4. 7.4 Device Functional Modes
      1. 7.4.1 Sleep Mode
      2. 7.4.2 PFM Mode
  9. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Power Train Components
        1. 8.1.1.1 Power MOSFETs
        2. 8.1.1.2 Buck Inductor
        3. 8.1.1.3 Output Capacitors
        4. 8.1.1.4 Input Capacitors
        5. 8.1.1.5 EMI Filter
      2. 8.1.2 Error Amplifier and Compensation
    2. 8.2 Typical Applications
      1. 8.2.1 Design 1 – Dual 5V and 3.3V, 20A Buck Regulator for 12V Input Applications
        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 Custom Design With Excel Quickstart Tool
          3. 8.2.1.2.3 Inductor Calculations
          4. 8.2.1.2.4 Shunt Resistors
          5. 8.2.1.2.5 Ceramic Output Capacitors
          6. 8.2.1.2.6 Ceramic Input Capacitors
          7. 8.2.1.2.7 Feedback Resistors
          8. 8.2.1.2.8 Input Voltage UVLO Resistors
          9. 8.2.1.2.9 Compensation Components
        3. 8.2.1.3 Application Curves
      2. 8.2.2 Design 2 – Two-Phase, Single-Output Synchronous Buck Regulator
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
      3. 8.2.3 Design 3 – 12V, 25A, 400kHz, Two-Phase Buck Regulator for 24V Input Applications
        1. 8.2.3.1 Design Requirements
        2. 8.2.3.2 Detailed Design Procedure
        3. 8.2.3.3 Application Curves
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
        1. 8.4.1.1 Power Stage Layout
        2. 8.4.1.2 Gate Drive Layout
        3. 8.4.1.3 PWM Controller Layout
        4. 8.4.1.4 Thermal Design and Layout
        5. 8.4.1.5 Ground Plane Design
      2. 8.4.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Device Support
      1. 9.1.1 Third-Party Products Disclaimer
      2. 9.1.2 Development Support
        1. 9.1.2.1 Custom Design With WEBENCH® Tools
    2. 9.2 Documentation Support
      1. 9.2.1 Related Documentation
        1. 9.2.1.1 Low-EMI Design Resources
        2. 9.2.1.2 Thermal Design Resources
        3. 9.2.1.3 PCB Layout Resources
    3. 9.3 Receiving Notification of Documentation Updates
    4. 9.4 Support Resources
    5. 9.5 Trademarks
    6. 9.6 Electrostatic Discharge Caution
    7. 9.7 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

7.3.1 Input Voltage Range (VIN)

The LM25137 input voltage operating range is from 4V to 42V. The device is intended for step-down conversions from 12V and 24V automotive supply rails. The circuit in Figure 7-1 shows the essential components to implement an LM25137 based wide-VIN dual-output buck regulator using a single input supply.

The LM25137 uses an internal LDO subregulator to provide a 5V VCC bias rail for the gate drive and control circuits (assuming the input voltage is higher than 5V plus the necessary subregulator dropout specification). There is also an integrated 20µA charge pump always active in LM25137. As VIN approaches the VOUT setpoint, the 20µA charge pump charges the CBOOT and keeps the high-side MOSFET on, thus achieving true 100% duty cycle. This action allows for the lowest possible dropout voltage from input to output.

LM25137 LM25137 Dual-Output Regulator Schematic Figure 7-1 LM25137 Dual-Output Regulator Schematic

In high input voltage applications, make sure that the VIN, SW1, and SW2 pin voltages do not exceed the absolute maximum voltage rating of 47V during line or load transient events. Voltage excursions that exceed the Absolute Maximum Ratings can damage the IC. Proceed carefully during PCB board layout and use high-quality input bypass capacitors to minimize switch-voltage overshoot and ringing.