SNVSCR9 October   2024 LM61495T-Q1

ADVANCE INFORMATION  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison Table
  6. 5 Pin Configuration and Functions
  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 Timing Requirements
    7. 6.7 Switching Characteristics
    8. 6.8 Typical Characteristics
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Output Voltage Selection
      2. 7.3.2  Enable EN Pin and Use as VIN UVLO
      3. 7.3.3  SYNC/MODE Uses for Synchronization
      4. 7.3.4  Clock Locking
      5. 7.3.5  Adjustable Switching Frequency
      6. 7.3.6  RESET Output Operation
      7. 7.3.7  Internal LDO, VCC UVLO, and BIAS Input
      8. 7.3.8  Bootstrap Voltage and VCBOOT-UVLO (CBOOT Pin)
      9. 7.3.9  Adjustable SW Node Slew Rate
      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 Hiccup
      14. 7.3.14 Thermal Shutdown
    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 Peak Current Mode Operation
        2. 7.4.3.2 Auto Mode Operation
          1. 7.4.3.2.1 Diode Emulation
        3. 7.4.3.3 FPWM Mode Operation
        4. 7.4.3.4 Minimum On-time (High Input Voltage) Operation
        5. 7.4.3.5 Dropout
        6. 7.4.3.6 Recovery from Dropout
        7. 7.4.3.7 Other Fault Modes
  9. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1  Choosing the Switching Frequency
        2. 8.2.2.2  Setting the Output Voltage
        3. 8.2.2.3  Inductor Selection
        4. 8.2.2.4  Output Capacitor Selection
        5. 8.2.2.5  Input Capacitor Selection
        6. 8.2.2.6  BOOT Capacitor
        7. 8.2.2.7  BOOT Resistor
        8. 8.2.2.8  VCC
        9. 8.2.2.9  CFF and RFF Selection
        10. 8.2.2.10 RSPSP Selection
        11. 8.2.2.11 RT Selection
        12. 8.2.2.12 RMODE Selection
        13. 8.2.2.13 External UVLO
        14. 8.2.2.14 Maximum Ambient Temperature
      3. 8.2.3 Application Curves
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
        1. 8.4.1.1 Ground and Thermal Considerations
      2. 8.4.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Device Support
      1. 9.1.1 Third-Party Products Disclaimer
    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 Glossary
    7. 9.7 Electrostatic Discharge Caution
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information
    1. 11.1 Tape and Reel Information

Package Options

Mechanical Data (Package|Pins)
  • VAM|16
Thermal pad, mechanical data (Package|Pins)
Orderable Information

7.4.3.5 Dropout

Dropout operation is defined as any input-to-output voltage ratio that requires frequency to drop to achieve the needed duty factor. At a given clock frequency, duty factor is limited by minimum off-time. After this limit is reached, if clock frequency is maintained, output voltage falls. Instead of allowing the output voltage to drop, the LM614xxT-Q1 extends on-time past the end of the clock cycle until the required peak inductor current is achieved. The clock can start a new cycle once peak inductor current is achieved or once a pre-determined maximum on-time, tON-MAX, of approximately 9µs passes. As a result, after the needed duty factor cannot be achieved at the selected clock frequency due to the existence of a minimum off-time, frequency drops to maintain regulation. If input voltage is low enough that the output voltage cannot be regulated even with an on-time of tON_MAX, output voltage drops to slightly below input voltage, VDROP1. See Section 6.

LM61480T-Q1 LM61495T-Q1 Frequency and Output Voltage in Dropout
Output voltage and frequency versus input voltage: if there is little difference between input voltage and output voltage setting, the IC reduces frequency to maintain regulation. If input voltage is too low to provide the desired output voltage at approximately 110kHz, output voltage tracks input voltage.
Figure 7-24 Frequency and Output Voltage in Dropout
LM61480T-Q1 LM61495T-Q1 Dropout Waveforms
This image shows the switching waveforms while in dropout. Inductor current takes longer than a normal clock to reach the desired peak value. As a result, frequency drops. This frequency drop is limited by tON_MAX.
Figure 7-25 Dropout Waveforms