SNVSC41 November   2023 LMR36500

PRODMIX  

  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 (Commercial) Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 System Characteristics
    7. 6.7 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 Enable, Shutdown, and Start-up
      2. 7.3.2 Adjustable Switching Frequency (with RT)
      3. 7.3.3 Power-Good Output Operation
      4. 7.3.4 Internal LDO, VCC UVLO, and VOUT/FB Input
      5. 7.3.5 Bootstrap Voltage and VBOOT-UVLO (BOOT Terminal)
      6. 7.3.6 Output Voltage Selection
      7. 7.3.7 Soft Start and Recovery from Dropout
        1. 7.3.7.1 Soft Start
        2. 7.3.7.2 Recovery from Dropout
      8. 7.3.8 Current Limit and Short Circuit
      9. 7.3.9 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 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 Reduction
        3. 7.4.3.3 FPWM Mode - Light Load Operation
        4. 7.4.3.4 Minimum On-time Operation
        5. 7.4.3.5 Dropout
  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
          1. 8.2.2.2.1 VOUT / FB for Adjustable Output
        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  CBOOT
        7. 8.2.2.7  VCC
        8. 8.2.2.8  CFF Selection
        9. 8.2.2.9  External UVLO
        10. 8.2.2.10 Maximum Ambient Temperature
      3. 8.2.3 Application Curves
    3. 8.3 Best Design Practices
    4. 8.4 Power Supply Recommendations
    5. 8.5 Layout
      1. 8.5.1 Layout Guidelines
        1. 8.5.1.1 Ground and Thermal Considerations
      2. 8.5.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Device Support
      1. 9.1.1 Device Nomenclature
    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

Package Options

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

7.3.7.1 Soft Start

The soft-start feature allows the LMR3650x family of devices to gradually reach the steady state output voltage, reducing the startup stress in the system. Soft start is triggered by any of the following conditions:

  • Voltage is applied to the VIN pin of the device, releasing undervoltage lockout.
  • EN/UVLO voltage is sufficient to enter active mode.
  • Recovery from shutdown due to over temperature protection.

After soft start is triggered, the internal reference is slowly ramped up. Assuming the output voltage is initially 0 V, the reference is ramped to 90% of the target output voltage in tSS. During the soft-start time the switching mode is set to AUTO mode. AUTO mode activates diode emulation for the low-side MOSFET, not allowing negative inductor current. This allows the output voltage to be pre-biased, voltage already present on the output, during startup without discharging the output capacitor. Figure 7-7 shows the difference between a non biased soft start and a pre-biased soft start.

GUID-FE56FC57-E0AB-4AFA-8975-C0CDE3698673-low.gif Figure 7-7 Soft Start with and Without Pre-biased Voltage