SNVSBK9D November   2019  – September 2022 LM63635-Q1

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
  7. 7 Specifications
    1.     Absolute Maximum Ratings
    2. 7.1 ESD Ratings
    3. 7.2 Recommended Operating Conditions
    4.     Thermal Information
    5.     Electrical Characteristics
    6.     Timing Characteristics
    7.     Switching Characteristics
    8. 7.3 System Characteristics
    9. 7.4 Typical Characteristics
  8. 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. 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 Device Support
      1. 12.1.1 Device Nomenclature
    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 Glossary
    7. 12.7 Electrostatic Discharge Caution
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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

8.3.2 Output Voltage Selection

The output voltage of the LM63635D-Q1 is set by the condition of the VSEL input. The condition of this input is tested when the device is first enabled. Once the converter is running, the voltage selection is fixed and cannot be changed until the next power-on cycle. Table 8-2 shows the selection programming. The LM63635D-Q1 contains an integrated voltage divider connected to the FB input. The converter regulates the voltage on the FB input to 5-V, 3.3-V, or 1-V, as selected. In ADJ mode, the voltage on the FB input is regulated to 1-V and the internal divider is disabled. In this case, an external voltage divider is used to set the desired output voltage anywhere within the recommended operating range. ADJ mode is programmed by connecting 10 kΩ from the VSEL input to ground. Although not recommenced, if this input is left floating, the device enters ADJ mode. See Section 9.2.2.2 for details of selecting the FB divider resistors.

For the LM63635C-Q1 variant, the output voltage is set by external feedback resistors and does not have the VSEL pin. See Section 7 for ensured specifications regarding the accuracy of the FB voltage and input current to the FB pin.

Providing internal voltage dividers for the 5-V and 3.3-V modes saves external components, reducing both board space and component cost. The relatively large values of the internal dividers reduce the load on the output, helping to improve the light load efficiency of the converter. In addition, since the divider is inside the device, it is less likely to pick up externally generated noise.

Table 8-2 Output Voltage Settings
VSEL INPUTOUTPUT VOLTAGE
VCC5 V
AGND3.3 V
10 kΩ to AGNDADJ
Float (not recommended)ADJ