SNVSAA7B December   2015  – July 2021 LM53625-Q1 , LM53635-Q1

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison
  6. 6 Pin Configuration and Functions
  7. 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 System Characteristics
    7. 7.7 Timing Characteristics
    8. 7.8 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
      1. 8.2.1 Control Scheme
    3. 8.3 Feature Description
      1. 8.3.1 RESET Flag Output
      2. 8.3.2 Enable and Start-Up
      3. 8.3.3 Soft-Start Function
      4. 8.3.4 Current Limit
      5. 8.3.5 Hiccup Mode
      6. 8.3.6 Synchronizing Input
      7. 8.3.7 Undervoltage Lockout (UVLO) and Thermal Shutdown (TSD)
      8. 8.3.8 Input Supply Current
    4. 8.4 Device Functional Modes
      1. 8.4.1 AUTO Mode
      2. 8.4.2 FPWM Mode
      3. 8.4.3 Dropout
      4. 8.4.4 Input Voltage Frequency Foldback
    5. 8.5 Spread-Spectrum Operation
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Applications
      1. 9.2.1 General Application
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
          1. 9.2.1.2.1 External Components Selection
            1. 9.2.1.2.1.1 Input Capacitors
              1. 9.2.1.2.1.1.1 Input Capacitor Selection
            2. 9.2.1.2.1.2 Output Inductors and Capacitors Selection
              1. 9.2.1.2.1.2.1 Inductor Selection
              2. 9.2.1.2.1.2.2 Output Capacitor Selection
          2. 9.2.1.2.2 Setting the Output Voltage
            1. 9.2.1.2.2.1 FB for Adjustable Versions
          3. 9.2.1.2.3 VCC
          4. 9.2.1.2.4 BIAS
          5. 9.2.1.2.5 CBOOT
          6. 9.2.1.2.6 Maximum Ambient Temperature
        3. 9.2.1.3 Application Curves
      2. 9.2.2 Fixed 5-V Output for USB-Type Applications
        1. 9.2.2.1 Design Requirements
        2. 9.2.2.2 Detailed Design Procedure
        3. 9.2.2.3 Application Curves
      3. 9.2.3 Fixed 3.3-V Output
        1. 9.2.3.1 Design Requirements
        2. 9.2.3.2 Detailed Design Procedure
        3. 9.2.3.3 Application Curves
      4. 9.2.4 Adjustable Output
        1. 9.2.4.1 Design Requirements
        2. 9.2.4.2 Detailed Design Procedure
        3. 9.2.4.3 Application Curves
    3. 9.3 What to Do and What Not to Do
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Third-Party Products Disclaimer
    2. 12.2 Documentation Support
      1. 12.2.1 Related Documentation
    3. 12.3 Receiving Notification of Documentation Updates
    4. 12.4 Support Resources
    5. 12.5 Trademarks
    6. 12.6 Electrostatic Discharge Caution
    7. 12.7 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

9.2.4.2 Detailed Design Procedure

  • BIAS is connected to the output. This example assumes that inductive short are a risk for this application so a 3-Ω resistor is added between BIAS and the output. A 0.1-µF capacitor is added close the BIAS pin.
  • FB is connected to the output through a voltage divider in order to create a voltage of 1 V at the FB pin when the output is at 6 V. A 12-pF capacitance is added in parallel with the top feedback resistor in order to improve transient behavior. BIAS and FB are connected to the output via separate traces. This is important to reduce noise and achieve good performances. See Section 11.1 for more details on the proper layout method.
  • SYNC is connected to ground directly as there is no need for this function in this application.
  • EN is toggled by an external device (like an MCU for example). A pulldown resistor is placed to ensure the part does not turn on if the external source is not driving the pin (Hi-Z condition).
  • FPWM is connected to GND. This leads the device to operate in AUTO mode. In this mode, the switching frequency is adjusted at light loads to keep efficiency maximum. As a result the switching frequency changes with the output current until medium load is reached. The device then switches at the frequency defined by FSW. See Section 8.4 for more details.
  • A 4.7-µF capacitor is connected between VCC and GND close to the VCC pin. This ensure stable operation of the internal LDO.
  • RESET is not used in this example so the pin has been left floating. Other possible connections can be seen in the previous typical applications and in Section 8.3.1.
  • Power components (input capacitor, output capacitor, and inductor) selection can be found here in Section 9.2.1.2.1.