SNVSBW1C December   2021  – August 2024 LM63440-Q1 , LM63460-Q1

PRODUCTION DATA  

  1.   1
  2. Features
  3. Applications
  4. Description
  5. Device Comparison Table
  6. Pin Configuration and Functions
    1. 5.1 Wettable Flanks
    2. 5.2 Pinout Design for Clearance and FMEA
  7. 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 Timing Characteristics
    7. 6.7 Systems Characteristics
    8. 6.8 Typical Characteristics
  8. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Input Voltage Range (VIN1, VIN2)
      2. 7.3.2  Output Voltage Setpoint (FB)
      3. 7.3.3  Precision Enable and Input Voltage UVLO (EN/SYNC)
      4. 7.3.4  Frequency Synchronization (EN/SYNC)
      5. 7.3.5  Clock Locking
      6. 7.3.6  Adjustable Switching Frequency (RT)
      7. 7.3.7  Power-Good Monitor (PGOOD)
      8. 7.3.8  Bias Supply Regulator (VCC, BIAS)
      9. 7.3.9  Bootstrap Voltage and UVLO (CBOOT)
      10. 7.3.10 Spread Spectrum
      11. 7.3.11 Soft Start and Recovery From Dropout
      12. 7.3.12 Overcurrent and Short-Circuit Protection
      13. 7.3.13 Thermal Shutdown
      14. 7.3.14 Input Supply Current
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown Mode
      2. 7.4.2 Standby Mode
      3. 7.4.3 Active Mode
        1. 7.4.3.1 CCM Mode
        2. 7.4.3.2 AUTO Mode – Light-Load Operation
          1. 7.4.3.2.1 Diode Emulation
          2. 7.4.3.2.2 Frequency Foldback
        3. 7.4.3.3 FPWM Mode – Light-Load Operation
        4. 7.4.3.4 Minimum On-Time (High Input Voltage) Operation
        5. 7.4.3.5 Dropout
  9. Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Design 1 – Automotive Synchronous 6A Buck Regulator at 2.1MHz
        1. 8.2.1.1 Design Requirements
      2. 8.2.2 Design 2 – Automotive Synchronous 4A Buck Regulator at 2.1MHz
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
          1. 8.2.2.2.1  Custom Design With WEBENCH® Tools
          2. 8.2.2.2.2  Setting the Output Voltage
          3. 8.2.2.2.3  Choosing the Switching Frequency
          4. 8.2.2.2.4  Inductor Selection
          5. 8.2.2.2.5  Output Capacitor Selection
          6. 8.2.2.2.6  Input Capacitor Selection
          7. 8.2.2.2.7  Bootstrap Capacitor
          8. 8.2.2.2.8  VCC Capacitor
          9. 8.2.2.2.9  BIAS Power Connection
          10. 8.2.2.2.10 Feedforward Network
          11. 8.2.2.2.11 Input Voltage UVLO
        3. 8.2.2.3 Application Curves
      3. 8.2.3 Design 3 – Automotive Synchronous 6A Buck Regulator at 400kHz
        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 Thermal Design and Layout
      2. 8.4.2 Layout Example
  10. 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
    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

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information
Inductor Selection

The parameters for selecting the inductor are the inductance and saturation current. The inductance is based on the desired peak-to-peak ripple current, which is normally chosen to be in the range of 20% to 40% of the maximum output current. Experience shows that the best value for inductor ripple current is 30% of the maximum load current for systems with a fixed input voltage. For systems with a variable input voltage such as the 12V automotive battery, 25% is commonly used.

When selecting the ripple current for applications with lower maximum load than the maximum available from the device, the maximum device current must still be used. For the 4A device, use Equation 7 to determine the value of inductance. The constant K is the percentage of peak-to-peak inductor current ripple to rated output current. Choose K = 0.3 for this 5V, 4A, 2.1MHz example, resulting in an inductance of approximately 1.2µH.

Equation 7. LM63440-Q1 LM63460-Q1

For the 6A device, use Equation 11 to determine the value of inductance. The constant K is the percentage of peak-to-peak inductor current ripple to rated output current. Choose K = 0.3 for this 5V, 6A, 2.1MHz example, resulting in an inductance of approximately 0.8µH.

Equation 8. LM63440-Q1 LM63460-Q1

The saturation current rating of the inductor must be higher than the high-side switch current limit, IL-HS (see the Electrical Characteristics). These requirements prevent inductor saturation during an overload condition on the output. While an output short-circuit condition causes the LM63440-Q1 or LM63460-Q1 to enter hiccup mode, an overload condition can hold the output current at current limit without triggering hiccup. When the inductor core material saturates, the inductance can fall to a low value, causing the inductor current to rise rapidly. Although the valley current limit, IL-LS, reduces the risk of current runaway, a saturated inductor causes the instantaneous current to increase to a high value. This can lead to component damage, avoiding inductor saturation is crucial.

Inductors with a ferrite core material have hard saturation characteristics but usually have lower core losses than powdered iron cores. Powdered iron cores exhibit a soft saturation, allowing some relaxation in the current rating of the inductor. However, powdered iron cores typically have higher core losses at frequencies above 1MHz.

To avoid subharmonic oscillation, the inductance value must not be less than that given by Equation 9. The maximum inductance is limited by the minimum current ripple required for current-mode control to perform correctly. As a rule-of-thumb, the minimum inductor ripple current must be no less than about 10% of the converter maximum rated current under nominal conditions.

Equation 9. LM63440-Q1 LM63460-Q1

Equation 9 assumes that this design must operate with the input voltage near or in dropout. Use Equation 10 instead if the minimum input voltage for a given design is high enough to limit the duty cycle to less than 40%.

Equation 10. LM63440-Q1 LM63460-Q1