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

8.2.3.1 Design Requirements

Table 8-6 shows the intended input, output, and performance parameters for this circuit example.

Table 8-6 Design Parameters
DESIGN PARAMETERVALUE
Input voltage range (steady state)18V to 34V
Minimum transient input voltage16V
Maximum transient input voltage36V
Output voltage12V
Output current30A
Switching frequency400kHz
Target efficiency at 25A 97%
Input voltage UVLO on, off15V, 13V
No-load sleep current with phase 2 disabled< 20µA
Shutdown current4µA

Resistor RRT of 57.6kΩ sets the switching frequency at 400kHz. In terms of control loop performance, the target loop crossover frequency is 60kHz with a phase margin greater than 50°. An RSS resistance of 20kΩ sets the output voltage soft-start time to 4.5ms.

the following table cites the selected buck regulator powertrain components, with many of the components available from multiple vendors. This design uses 40V logic-level MOSFETs, shielded buck inductors, shunt resistors with wide aspect ratio for low ESL, 50V-rated ceramic input capacitors and 25V-rated ceramic output capacitors.

Table 8-7 List of Materials for Application Circuit 3
REFERENCE DESIGNATORQTYSPECIFICATION(1)MANUFACTURERPART NUMBER
CIN1, CIN2 810µF, 50V, X7R, 1210, ceramicTDKCNA6P1X7R1H106K
10µF, 50V, X7S, 1210, ceramicMurataGCM32EC71H106K
COUT1, COUT2 8 22µF, 25V, X7R, 1210, ceramicTDKCGA6P3X7R1E226M250
22µF, 25V, X7S, 1210, ceramicMurataGCM32EC71E226KE36
LO1, LO223.3µH, 6.2mΩ, 19A, 10.85 × 10 × 5.2mmCyntecVCHA105D-3R3MS6
3.3µH, 6.2mΩ, 20A, 11 × 10 × 5.1mm Bourns SRP1050WA-3R3M
3.3µH, 6mΩ, 28.6A, 10.5 × 10 × 6.5mmTDKSPM10065VT-3R3M-D
3.3µH, 9.23mΩ, 16A, 10.8 × 10 × 5mm Eaton HCM1A1105V2-3R3-R
3.3µH, 9.9mΩ, 22.1A, 10.85 × 10 × 3.8mmWürth Electronik784373680033
Q1, Q2,Q3, Q4440V, 3.6mΩ, 9nC, SON 5 × 6InfineonIAUCN04S7L028ATMA1
RS1, RS22Shunt, 3mΩ ±1%, ±50ppm/°C, 0612 wide aspect ratio, 1.5WSusumuKRL3216E-C-R003-F
U11LM25137 42V two-phase synchronous buck controllerTexas InstrumentsLM25137RHAR
(1) See Third-Party Products Disclaimer.