SNVSCF0A October   2024  – December 2025 LM65680-Q1

ADVANCE INFORMATION  

  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
    2. 5.2 Pinout Design for Clearance and FMEA
  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 Descriptions
      1. 7.3.1  Input Voltage Range (VIN1, VIN2)
      2. 7.3.2  High-Voltage Bias Supply Subregulator (VCC, BIAS)
      3. 7.3.3  Precision Enable and Adjustable Input Voltage UVLO (EN/UVLO)
      4. 7.3.4  Output Voltage Setpoint (FB, BIAS)
      5. 7.3.5  Switching Frequency (RT)
      6. 7.3.6  Mode Selection and Clock Synchronization (MODE/SYNC)
        1. 7.3.6.1 Clock Synchronization
        2. 7.3.6.2 Clock Locking
      7. 7.3.7  Device Configuration (CNFG/SYNCOUT)
      8. 7.3.8  Dual-Random Spread Spectrum (DRSS)
      9. 7.3.9  High-Side MOSFET Gate Drive (BST)
      10. 7.3.10 Configurable Soft Start (SS)
        1. 7.3.10.1 Recovery From Dropout
      11. 7.3.11 Protection Features
        1. 7.3.11.1 Power-Good Monitor (PG)
        2. 7.3.11.2 Overcurrent and Short-Circuit Protection
        3. 7.3.11.3 Hiccup-Mode Protection
        4. 7.3.11.4 Thermal Shutdown
      12. 7.3.12 Two-Phase, Single-Output Operation
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown Mode
      2. 7.4.2 Active Mode
  9. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Power Train Components
        1. 8.1.1.1 Buck Inductor
        2. 8.1.1.2 Output Capacitors
        3. 8.1.1.3 Input Capacitors
        4. 8.1.1.4 EMI Filter
      2. 8.1.2 Error Amplifier and Compensation
      3. 8.1.3 Maximum Ambient Temperature
        1. 8.1.3.1 Derating Curves
    2. 8.2 Typical Applications
      1. 8.2.1 Design 1 – 5V, 8A Synchronous Buck Regulator With Wide Input Voltage Range and High Efficiency
        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  Choosing the Switching Frequency
          3. 8.2.1.2.3  Buck Inductor Selection
          4. 8.2.1.2.4  Input Capacitor Selection
          5. 8.2.1.2.5  Output Capacitors
          6. 8.2.1.2.6  Output Voltage Setpoint
          7. 8.2.1.2.7  Compensation Components
          8. 8.2.1.2.8  Setting the Input Voltage UVLO
          9. 8.2.1.2.9  EMI Mitigation, RDRSS
          10. 8.2.1.2.10 Bootstrap Capacitor, CBST
        3. 8.2.1.3 Application Curves
      2. 8.2.2 Design 2 – High Efficiency, 48V to 12V, 8A, 400kHz Synchronous Buck Regulator
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
          1. 8.2.2.2.1 Buck Inductor Selection
          2. 8.2.2.2.2 Input Capacitor Selection
          3. 8.2.2.2.3 Output Capacitors
          4. 8.2.2.2.4 Output Voltage Setpoint
          5. 8.2.2.2.5 Compensation Components
          6. 8.2.2.2.6 Feedforward Capacitor
          7. 8.2.2.2.7 Soft-Start Capacitor
        3. 8.2.2.3 Application Curves
    3. 8.3 Best Design Practices
    4. 8.4 Power Supply Recommendations
    5. 8.5 Layout
      1. 8.5.1 Layout Guidelines
        1. 8.5.1.1 Thermal Design and Layout
      2. 8.5.2 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 Multiphase Design Resources
        4. 9.2.1.4 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
    1. 11.1 Tape and Reel Information

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8.2.1.1 Design Requirements

Table 8-5 shows the specifications for a 5V, 8A buck regulator with a switching frequency of 400kHz. In this example, the target half-load and full-load efficiencies are 92% and 90%, respectively, based on a nominal input voltage of 48V that ranges from 9V to 60V steady state, with short-term transients as low as 6.5V and as high as 70V.

Table 8-5 Detailed Design Parameters
DESIGN PARAMETER VALUE
Input voltage range (steady state) 9V to 60V
Minimum transient input voltage (cold crank) 6.5V
Maximum transient input voltage (load dump) 65V
Input UVLO turn-on threshold 5.9V
Output voltage 5V
Output current 0A to 8A
Switching frequency 400kHz
Soft-start time 5.3ms (default internal setting)
EMI mitigation DRSS off, slew-rate control on
Ambient temperature range –40°C to 85°C

Resistor RRT of 40.2kΩ sets the free-running switching frequency at 400kHz, and an optional SYNC input signal allows adjustment of the switching frequency from 320kHz to 480kHz for this specific application. Leaving the SS pin open sets the soft-start time to the fixed internal setting of 5.3ms. In terms of control loop performance, the target loop crossover frequency is 60kHz with a phase margin greater than 50°.

Table 8-8 cites the selected buck regulator powertrain components, with many of the components available from multiple vendors. This design uses a low-DCR inductor with composite core material and an all-ceramic output capacitor implementation.

Table 8-6 List of Materials for Application Circuit 1
REFERENCE DESIGNATOR QTY SPECIFICATION VENDOR(1) PART NUMBER
CIN1, CIN2 4 4.7μF, 100V, X7S, 1210, ceramic, AEC-Q200 Murata GCM32DC72A475K
TDK CGA6M3X7S2A475K
CIN-HF1, CIN-HF2 2 100nF, 100V, X7R, 0603, ceramic, AEC-Q200 Murata GCJ188R72A104M
COUT 2 47μF, 10V, X7S, 1210, ceramic, AEC-Q200 Murata GCM32EC71A476K
TDK CNA6P1X7S1A476M
LO 1 3.3µH, 5.9mΩ, 13.4A, 6.71 × 6.51 × 6.1mm, AEC-Q200 Coilcraft XGL6060-332MEC
3.3µH, 6mΩ, 15.6A, 6.6 × 6.4 × 6.1mm, AEC-Q200 Würth Elektronik 744393465033
3.3µH, 6.3mΩ, 16A, 6.6 × 6.4 × 6mm, AEC-Q200 XFMRS XFHCL6060HC-3R3M
3.3µH, 8.4mΩ, 18.6A, 8.05 × 7.5 × 5.4mm, AEC-Q200 Cyntec VCHD075D-3R3MS6
4.7µH, 5.7mΩ, 26.5A, 11.3 × 10 × 6mm, AEC-Q200 Würth Elektronik 744393665047
U1 1 LM65680-Q1 65V, 8A synchronous buck converter, AEC-Q100 Texas Instruments LM65680