SNVS667I February   2010  – March 2022 LMZ12010

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 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 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Output Overvoltage Protection
      2. 7.3.2 Current Limit
      3. 7.3.3 Thermal Protection
      4. 7.3.4 Prebiased Start-Up
    4. 7.4 Device Functional Modes
      1. 7.4.1 Discontinuous Conduction and Continuous Conduction Modes
  8. 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 Enable Divider, RENT, RENB, and RENH Selection
        2. 8.2.2.2 Output Voltage Selection
        3. 8.2.2.3 Soft-Start Capacitor Selection
        4. 8.2.2.4 Tracking Supply Divider Option
        5. 8.2.2.5 COUT Selection
        6. 8.2.2.6 CIN Selection
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Examples
    3. 10.3 Power Dissipation and Thermal Considerations
    4. 10.4 Power Module SMT Guidelines
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
      2. 11.1.2 Development Support
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Support Resources
    4. 11.4 Receiving Notification of Documentation Updates
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

8.2.2.3 Soft-Start Capacitor Selection

Programmable soft start permits the regulator to slowly ramp to its steady-state operating point after being enabled, thereby reducing current inrush from the input supply and slowing the output voltage rise time.

Upon turn-on, after all UVLO conditions have been passed, an internal 1.6-ms circuit slowly ramps the SS input to implement internal soft start. If 1.6 ms is an adequate turn-on time, then the CSS capacitor can be left unpopulated. Longer soft-start periods are achieved by adding an external capacitor to this input.

Soft-start duration is given by the formula:

Equation 8. tSS = VREF × CSS / ISS = 0.795 V × CSS / 50 µA

This equation can be rearranged as follows:

Equation 9. CSS = tSS × 50 μA / 0.795 V

Using a 0.22-μF capacitor results in 3.5-ms typical soft-start duration and 0.47 μF results in 7.5 ms typical. 0.47 μF is a recommended initial value.

As the soft-start input exceeds 0.795 V, the output of the power stage will be in regulation and the 50-μA current is deactivated. Note that the following conditions will reset the soft-start capacitor by discharging the SS input to ground with an internal current sink.

  • The Enable input being pulled low
  • A thermal shutdown condition
  • VIN falling below 4.3 V (typical) and triggering the VCC UVLO