SNVSBW0B October   2022  – August 2024 LM64440-Q1 , LM64460-Q1

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison Table
  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 Timing Characteristics
    7. 6.7 Systems 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  Input Voltage Range (VIN1, VIN2)
      2. 7.3.2  Output Voltage Setpoint (FB)
      3. 7.3.3  Precision Enable and Input Voltage UVLO (EN)
      4. 7.3.4  MODE/SYNC Operation
        1. 7.3.4.1 Level-Dependent MODE/SYNC Control
        2. 7.3.4.2 Pulse-Dependent MODE/SYNC Control
      5. 7.3.5  Clock Locking
      6. 7.3.6  Power-Good Monitor (PGOOD)
      7. 7.3.7  Bias Supply Regulator (VCC, BIAS)
      8. 7.3.8  Bootstrap Voltage and UVLO (CBOOT)
      9. 7.3.9  Spread Spectrum
      10. 7.3.10 Soft Start and Recovery From Dropout
      11. 7.3.11 Overcurrent and Short-Circuit Protection
      12. 7.3.12 Thermal Shutdown
      13. 7.3.13 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. 8 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. 8.3 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. 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
    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

7.3.10 Soft Start and Recovery From Dropout

The converter uses a reference-based soft start that prevents output voltage overshoot and large inrush current during start-up. Soft start is triggered by any of the following conditions:

  • Power is applied to the VIN pins of the IC, releasing UVLO.
  • EN goes high to turn on the device.
  • Recovery from a hiccup-waiting period
  • Recovery from thermal shutdown protection

After soft start is triggered, the IC takes the following actions:

  • The reference used by the IC to regulate the output voltage is slowly ramped. The net result is that the output voltage takes tSS to reach 90% of the desired value.
  • The operating mode is set to AUTO, activating diode emulation. This action allows a pre-biased start-up without pulling the output voltage low if there is a voltage already present on the output.

Together, these actions provide start-up with limited inrush currents and also facilitate the use of high output capacitance and higher loading conditions that cause the peak inductor current to border on current limit during start-up without triggering hiccup. See Figure 7-14.

LM64440-Q1 LM64460-Q1 Soft-Start Operation
Soft start functions with the output voltage starting from 0V in (a), or if there is already a prebiased output as shown in (b). In either case, the output voltage must reach within 10% of the setpoint within tSS after soft start initiates. FPWM and hiccup are disabled during soft start, with both FPWM and hiccup enabled after the output voltage reaches regulation or after the tSS2 time interval expires, whichever happens first.
Figure 7-14 Soft-Start Operation

Any time the output voltage falls more than a few percent, the output voltage ramps up slowly. This condition is called recovery from dropout and differs from soft start in three important ways:

  • The reference voltage is set to approximately 1% above what is needed to achieve the preset output voltage setpoint.
  • Hiccup is allowed if the output voltage is less than 40% of the nominal setpoint. Note that during dropout regulation, hiccup is inhibited.
  • FPWM mode is allowed during recovery from dropout. If the output voltage were to suddenly be pulled up by an external supply, the converter can pull down on the output.

Despite being called recovery from dropout, this feature is active whenever the output voltage drops to a few percent lower than the setpoint. This action primarily occurs under the following conditions:

  • Dropout: When there is insufficient input voltage to maintain the desired output voltage
  • Overcurrent: When there is an overcurrent event that is not severe enough to trigger hiccup
LM64440-Q1 LM64460-Q1 Recovery From Dropout
Whether the output voltage falls due to high load current or low input voltage, after the condition that causes the output to fall below the setpoint is removed, the output recovers at the same rate as during start-up. Even though hiccup does not trigger due to dropout, it can, in principle, be triggered during recovery if output voltage is below 40% of the output voltage setpoint for more than 128 clock cycles.
Figure 7-15 Recovery From Dropout