SNVSCF0B October   2024  – May 2026 LM65680-Q1

ADVMIX  

  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

8.4 Power Supply Recommendations

The characteristics of the input supply must be capable of delivering the required input current to the loaded regulator. The average input current can be estimated with the following equation.

Equation 57. IIN=VOUT×IOUTVIN×ƞ

where

η is the efficiency.

If the regulator connects to the input supply through long wires or PCB traces, take special care to achieve good performance. The parasitic inductance and resistance of the input cables can have an adverse effect on the operation of the regulator. The parasitic inductance, in combination with the low-ESR ceramic input capacitors, can form an underdamped resonant circuit. This can result in overvoltage transients at the input to the regulator or tripping UVLO. Consider that the supply voltage can dip when a load transient is applied to the output, depending on the parasitic resistance and inductance of the harness and characteristics of the supply. If the application is operating close to the minimum input voltage, this dip can cause the regulator to momentarily shut down and reset. The best way to resolve such issues is to reduce the distance from the input supply to the regulator. Additionally, use an aluminum input capacitor in parallel with the ceramics. The moderate ESR of this type of capacitor helps damp the input resonant circuit and reduce any overshoots or undershoots. A value in the range of 22µF to 68µF is usually sufficient to provide input damping and help hold the input voltage steady during large load transients.

The input voltage must not be allowed to fall below the output voltage. In this scenario, such as a shorted input test, the output capacitors discharge through the internal body diode found between the VIN and SW pins of the device. During this condition, the current can become uncontrolled, possibly causing damage to the device. If this scenario is considered likely, then use a Schottky diode between the output and the input supply.