SNVSBR8D March   2020  – June 2022 LMQ61460

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Timing Characteristics
    7. 7.7 Systems Characteristics
    8. 7.8 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  EN/SYNC Uses for Enable and VIN UVLO
      2. 8.3.2  EN/SYNC Pin Uses for Synchronization
      3. 8.3.3  Adjustable Switching Frequency
      4. 8.3.4  Clock Locking
      5. 8.3.5  PGOOD Output Operation
      6. 8.3.6  Internal LDO, VCC UVLO, and BIAS Input
      7. 8.3.7  Bootstrap Voltage and VCBOOT-UVLO (CBOOT Pin)
      8. 8.3.8  Adjustable SW Node Slew Rate
      9. 8.3.9  Spread Spectrum
      10. 8.3.10 Soft Start and Recovery From Dropout
      11. 8.3.11 Output Voltage Setting
      12. 8.3.12 Overcurrent and Short Circuit Protection
      13. 8.3.13 Thermal Shutdown
      14. 8.3.14 Input Supply Current
    4. 8.4 Device Functional Modes
      1. 8.4.1 Shutdown Mode
      2. 8.4.2 Standby Mode
      3. 8.4.3 Active Mode
        1. 8.4.3.1 CCM Mode
        2. 8.4.3.2 Auto Mode – Light-Load Operation
          1. 8.4.3.2.1 Diode Emulation
          2. 8.4.3.2.2 Frequency Reduction
        3. 8.4.3.3 FPWM Mode – Light-Load Operation
        4. 8.4.3.4 Minimum On-Time (High Input Voltage) Operation
        5. 8.4.3.5 Dropout
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1  Choosing the Switching Frequency
        2. 9.2.2.2  Setting the Output Voltage
        3. 9.2.2.3  Inductor Selection
        4. 9.2.2.4  Output Capacitor Selection
        5. 9.2.2.5  Input Capacitor Selection
        6. 9.2.2.6  BOOT Capacitor
        7. 9.2.2.7  BOOT Resistor
        8. 9.2.2.8  VCC
        9. 9.2.2.9  BIAS
        10. 9.2.2.10 CFF and RFF Selection
        11. 9.2.2.11 External UVLO
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
      1. 11.1.1 Ground and Thermal Considerations
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Support Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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

9.2.2.4 Output Capacitor Selection

The value of the output capacitor and its ESR determine the output voltage ripple and load transient performance. The output capacitor is usually determined by the load transient requirements rather than the output voltage ripple. Table 9-3 can be used to find the output capacitor and CFF selection for a few common applications. Note that a 1-kΩ RFF must be used in series with CFF. In this example, improved transient performance is desired giving 2 × 47-µF ceramic as the output capacitor and 22 pF as CFF.

Table 9-3 Recommended Output Ceramic Capacitors and CFF Values
FrequencyTransient Performance3.3-V Output5-V Output
Ceramic Output CapacitanceCFFCeramic Output CapacitanceCFF
2.1 MHzMinimum3 × 22 µF10 pF2 × 22 µF22 pF
2.1 MHzBetter Transient2 × 47 µF33 pF3 × 22 µF33 pF
400 kHzMinimum3 × 47 µF4.7 pF2 × 47 µF10 pF
400 kHzBetter Transient4 × 47 µF33 pF3 × 47 µF33 pF

To minimize ceramic capacitance, a low-ESR electrolytic capacitor can be used in parallel with minimal ceramic capacitance. As a starting point for designing with an output electrolytic capacitor, Table 9-4 shows the recommended output ceramic capacitance CFF values when using an electrolytic capacitor.

Table 9-4 Recommended Electrolytic and Ceramic Capacitor and CFF Values
FrequencyTransient Performance3.3-V Output5-V Output
COUTCFFCOUTCFF
400 kHzMinimum2 × 47-µF ceramic + 1 × 470 µF, 100-mΩ electrolytic10 pF3 × 22-µF ceramic + 1 × 470 µF, 100-mΩ electrolytic10 pF
400 kHzBetter Transient3 × 47-µF ceramic + 2 × 280 µF,100-mΩ electrolytic33 pF4 × 22 µF Ceramic + 1 × 560 µF, 100-mΩ electrolytic22 pF

Most ceramic capacitors deliver far less capacitance than the capacitor’s rating indicates. Be sure to check any capacitor selected for initial accuracy, temperature derating and voltage derating. Table 9-3 and Table 9-4 have been generated assuming typical derating for 16-V, X7R capacitors. If lower voltage, non-automotive grade, or lower temperature rated capacitors are used, more capacitors than listed are likely needed.