SNVSB70F May   2019  – June 2021 LM61460-Q1

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Description (continued)
  6. 6 Device Comparison Table
  7. 7 Pin Configuration and Functions
  8. 8 Specifications
    1. 8.1 Absolute Maximum Ratings
    2. 8.2 ESD Ratings
    3. 8.3 Recommended Operating Conditions
    4. 8.4 Thermal Information
    5. 8.5 Electrical Characteristics
    6. 8.6 Timing Characteristics
    7. 8.7 Systems Characteristics
    8. 8.8 Typical Characteristics
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1  EN/SYNC Uses for Enable and VIN UVLO
      2. 9.3.2  EN/SYNC Pin Uses for Synchronization
      3. 9.3.3  Clock Locking
      4. 9.3.4  Adjustable Switching Frequency
      5. 9.3.5  PGOOD Output Operation
      6. 9.3.6  Internal LDO, VCC UVLO, and BIAS Input
      7. 9.3.7  Bootstrap Voltage and VCBOOT-UVLO (CBOOT Pin)
      8. 9.3.8  Adjustable SW Node Slew Rate
      9. 9.3.9  Spread Spectrum
      10. 9.3.10 Soft Start and Recovery From Dropout
      11. 9.3.11 Output Voltage Setting
      12. 9.3.12 Overcurrent and Short Circuit Protection
      13. 9.3.13 Thermal Shutdown
      14. 9.3.14 Input Supply Current
    4. 9.4 Device Functional Modes
      1. 9.4.1 Shutdown Mode
      2. 9.4.2 Standby Mode
      3. 9.4.3 Active Mode
        1. 9.4.3.1 CCM Mode
        2. 9.4.3.2 Auto Mode - Light Load Operation
          1. 9.4.3.2.1 Diode Emulation
          2. 9.4.3.2.2 Frequency Reduction
        3. 9.4.3.3 FPWM Mode - Light Load Operation
        4. 9.4.3.4 Minimum On-time (High Input Voltage) Operation
        5. 9.4.3.5 Dropout
  10. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
        1. 10.2.2.1  Choosing the Switching Frequency
        2. 10.2.2.2  Setting the Output Voltage
        3. 10.2.2.3  Inductor Selection
        4. 10.2.2.4  Output Capacitor Selection
        5. 10.2.2.5  Input Capacitor Selection
        6. 10.2.2.6  BOOT Capacitor
        7. 10.2.2.7  BOOT Resistor
        8. 10.2.2.8  VCC
        9. 10.2.2.9  BIAS
        10. 10.2.2.10 CFF and RFF Selection
        11. 10.2.2.11 External UVLO
      3. 10.2.3 Application Curves
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
      1. 12.1.1 Ground and Thermal Considerations
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Documentation Support
      1. 13.1.1 Related Documentation
    2. 13.2 Receiving Notification of Documentation Updates
    3. 13.3 Support Resources
    4. 13.4 Trademarks
    5. 13.5 Electrostatic Discharge Caution
    6. 13.6 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

10.2.2.4 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 10-3 can be used to find the output capacitor and CFF selection for a few common applications. Note that a 1-kΩ RFF can be used in series with CFF to further improve noise performance. In this example, improved transient performance is desired giving 2 x 47-µF ceramic as the output capacitor and 22 pF as CFF.

Table 10-3 Recommended Output Ceramic Capacitors and CFF Values
FREQUENCY TRANSIENT PERFORMANCE 3.3-V OUTPUT 5-V OUTPUT
CERAMIC OUTPUT CAPACITANCE CFF CERAMIC OUTPUT CAPACITANCE CFF
2.1 MHz Minimum 3 x 22 µF 10 pF 2 x 22 µF 22 pF
2.1 MHz Better Transient 2 x 47 µF 33 pF 3 x 22 µF 33 pF
400 kHz Minimum 3 x 47 µF 4.7 pF 2 x 47 µF 10 pF
400 kHz Better Transient 3 x 47 µF 33 pF 3 x 47 µF 33 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 10-4 shows the recommended output ceramic capacitance CFF values when using an electrolytic capacitor.

Table 10-4 Recommended Electrolytic and Ceramic Capacitor and CFF Values
FREQUENCY TRANSIENT PERFORMANCE 3.3-V OUTPUT 5-V OUTPUT
COUT CFF COUT CFF
400 kHz Minimum 2 x 47 µF ceramic + 1 x 470 µF, 100-mΩ electrolytic 10 pF 3 x 22 µF ceramic + 1 x 470 µF, 100-mΩ electrolytic 10 pF
400 kHz Better Transient 3 x 47 µF ceramic + 2 x 280 µF,100-mΩ electrolytic 33 pF 4 x 22 µF ceramic + 1 x 560 µF, 100-mΩ electrolytic 22 pF

Most ceramic capacitors deliver far less capacitance than the rating of the capacitor indicates. Be sure to check any capacitor selected for initial accuracy, temperature derating, and voltage derating. Table 10-3 and Table 10-4 have been generated assuming typical derating for 16-V, X7R, automotive grade capacitors. If lower voltage, non-automotive grade, or lower temperature rated capacitors are used, more capacitors than listed are likely to be needed.