SNVS686L March   2011  – June 2025 LMZ22005

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 Synchronization Input
      2. 6.3.2 Output Overvoltage Protection
      3. 6.3.3 Current Limit
      4. 6.3.4 Thermal Protection
      5. 6.3.5 Prebiased Start-Up
    4. 6.4 Device Functional Modes
      1. 6.4.1 Discontinuous And Continuous Conduction Modes
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
        1. 7.2.2.1 Custom Design With WEBENCH® Tools
        2. 7.2.2.2 Design Steps
        3. 7.2.2.3 Enable Divider, RENT, RENB, and RENH Selection
        4. 7.2.2.4 Output Voltage Selection
        5. 7.2.2.5 Soft-start Capacitor Selection
        6. 7.2.2.6 Tracking Supply Divider Option
        7. 7.2.2.7 CO Selection
        8. 7.2.2.8 CIN Selection
        9. 7.2.2.9 Discontinuous and Continuous Conduction Modes Selection
      3. 7.2.3 Application Curves
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Examples
      3. 7.4.3 Power Dissipation and Thermal Considerations
      4. 7.4.4 Power Module SMT Guidelines
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Development Support
        1. 8.1.1.1 Custom Design With WEBENCH® Tools
    2. 8.2 Documentation Support
      1. 8.2.1 Related Documentation
    3. 8.3 Receiving Notification of Documentation Updates
    4. 8.4 Support Resources
    5. 8.5 Trademarks
    6. 8.6 Electrostatic Discharge Caution
    7. 8.7 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

Package Options

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

7.2.2.5 Soft-start Capacitor Selection

Programmable soft-start permits the regulator to slowly ramp to the 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 2-ms circuit slowly ramps the SS/TRK 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 6. tSS = VREF × CSS / Iss = 0.796 V × CSS / 50 µA

This equation can be rearranged as follows:

Equation 7. CSS = tSS × 50 μA / 0.796 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.

After the soft-start input exceeds 0.796 V, the output of the power stage is in regulation and the 50-μA current is deactivated. The following conditions reset the soft-start capacitor by discharging the SS input to ground with an internal current sink.

  • The Enable input being pulled low
  • Thermal shutdown condition
  • Internal VCC UVLO (Approx 4.3V input to VIN)