SNVSBK9C November   2019  – September 2020 LM63635-Q1

PRODUCTION DATA  

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Device Comparison Table
  6. Pin Configuration and Functions
    1.     Pin Functions
  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 Switching Characteristics
    8. 7.8 System Characteristics
    9. 7.9 Typical Characteristics
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Sync/Mode Selection
      2. 8.3.2 Output Voltage Selection
      3. 8.3.3 Switching Frequency Selection
        1. 8.3.3.1 Spread Spectrum Option
      4. 8.3.4 Enable and Start-up
      5. 8.3.5 RESET Flag Output
      6. 8.3.6 Undervoltage Lockout and Thermal Shutdown and Output Discharge
    4. 8.4 Device Functional Modes
      1. 8.4.1 Overview
      2. 8.4.2 Light Load Operation
        1. 8.4.2.1 Sync/FPWM Operation
      3. 8.4.3 Dropout Operation
      4. 8.4.4 Minimum On-time Operation
      5. 8.4.5 Current Limit and Short-Circuit Operation
  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
          1. 9.2.2.2.1 CFF Selection
        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 CBOOT
        7. 9.2.2.7 VCC
        8. 9.2.2.8 External UVLO
        9. 9.2.2.9 Maximum Ambient Temperature
      3. 9.2.3 Full Feature Design Example
      4. 9.2.4 Application Curves
      5. 9.2.5 EMI Performance Curves
    3. 9.3 What to Do and What Not to Do
  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 Glossary
    6. 12.6 Electrostatic Discharge Caution
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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

Enable and Start-up

Start-up and shutdown are controlled by the EN input. This input features precision thresholds, allowing the use of an external voltage divider to provide an adjustable input UVLO (see Section 9.2.2.8). Applying a voltage greater than VEN-VCC causes the device to enter standby mode, powering the internal VCC, but not producing an output voltage. Increasing the EN voltage to VEN-H fully enables the device, allowing it to enter start-up mode and begin the soft-start period. When the EN input is brought below VEN-L, the regulator stops running and enters standby mode. Further decrease in the EN voltage to below VEN-VCC completely shuts down the device. Figure 8-2 shows this behavior. The EN input can be connected directly to VIN if this feature is not needed. This input must not be allowed to float. The values for the various EN thresholds can be found in Section 7.

The LM63635-Q1 uses a reference-based soft start that prevents output voltage overshoots and large inrush currents as the regulator is starting up. Figure 8-3 shows a typical start-up waveform along with typical timings. Once EN goes high, there is a delay of about 1 ms before the soft-start period begins. The output voltage begins to rise and reaches the final value in about 1.5 ms (tss). After a delay of about 3 ms (trise-delay), the RESET flag goes high. During start-up, the device is not allowed to enter FPWM mode until the tss-done time has elapsed. This time is measured from the rising edge of EN.

GUID-A6BB7743-DA73-4B2A-8087-F1A23D4B6FD4-low.gifFigure 8-2 Precision Enable Behavior
GUID-FC6C56A6-CFC7-423E-83CA-0F4362F2CAB1-low.gifFigure 8-3 Typical Start-up Behavior VIN = 12 V, VOUT = 5 V, IOUT = 3.25 A