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

7.3.11 Overcurrent and Short-Circuit Protection

The converter protects from overcurrent conditions with cycle-by-cycle current limiting on both the high-side and the low-side MOSFETs. High-side MOSFET overcurrent protection is implemented by nature of peak-current mode control. The HS switch current is sensed when the HS switch is turned on after a short blanking time. Every switching cycle, this switch current is compared to the minimum of a fixed current setpoint or the output of the voltage regulation loop minus slope compensation. Because the voltage loop output has a maximum value and slope compensation increases with duty cycle, the HS current limit decreases with increased duty cycle when the duty cycle is above 35%. See Figure 7-16.

LM64440-Q1 LM64460-Q1 HS Switch Maximum Current as a Function of Duty Cycle for the LM64460-Q1 Figure 7-16 HS Switch Maximum Current as a Function of Duty Cycle for the LM64460-Q1

When the LS switch is turned on, the switch current is also sensed and monitored. Like the HS device, the LS switch turns off as commanded by the voltage control loop and low-side current limit. If the LS switch current is higher than IL-LS at the end of a switching cycle, the switching cycle is extended until the LS current reduces below the limit. The LS switch is turned off after the LS current falls below the limit, and the HS switch is turned on again as long as at least one clock period has passed since the last time the HS device has turned on.

LM64440-Q1 LM64460-Q1 Current Limit Waveforms Figure 7-17 Current Limit Waveforms

Because the current waveform assumes values between IL-HS and IL-LS, the maximum output current is very close to the average of these two values. Hysteretic control is used and current does not increase as output voltage approaches zero.

The converter employs hiccup overcurrent protection if there is an extreme overload, and the following conditions are met for 128 consecutive switching cycles:

  • The output voltage is below approximately 0.4 times the output voltage setpoint.
  • Greater than tSS2 has passed since soft start has started; see Soft Start and Recovery from Dropout.
  • The converter is not operating in dropout, which is defined as having minimum off time controlled duty cycle.

In hiccup mode, the device shuts down and attempts to soft start after tW. Hiccup mode helps reduce the device power dissipation under severe overcurrent conditions and short circuits. See Figure 7-18. After the overload is removed, the device recovers as though in soft start; see Figure 7-19.

LM64440-Q1 LM64460-Q1 Inductor Current Bursts During HiccupFigure 7-18 Inductor Current Bursts During Hiccup
LM64440-Q1 LM64460-Q1 Short-Circuit RecoveryFigure 7-19 Short-Circuit Recovery