SLVSHT0 May   2024 TPSM86637 , TPSM86638

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  The Adaptive On-Time Control and PWM Operation
      2. 6.3.2  Mode Selection
        1. 6.3.2.1 FCCM Control and Eco-mode Control
      3. 6.3.3  Soft Start and Prebiased Soft Start
      4. 6.3.4  Enable and Adjusting Undervoltage Lockout
      5. 6.3.5  Output Overcurrent Limit and Undervoltage Protection
      6. 6.3.6  Overvoltage Protection
      7. 6.3.7  UVLO Protection
      8. 6.3.8  Thermal Shutdown
      9. 6.3.9  Output Voltage Discharge
      10. 6.3.10 Power Good
      11. 6.3.11 Large Duty Operation
    4. 6.4 Device Functional Modes
      1. 6.4.1 Standby Operation
      2. 6.4.2 Light Load Operation
  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 Output Voltage Resistors Selection
        2. 7.2.2.2 Output Filter Selection
        3. 7.2.2.3 Input Capacitor Selection
      3. 7.2.3 Application Curves
    3. 7.3 Power Supply Recommendations
      1. 7.3.1 Application Thermal Considerations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Third-Party Products Disclaimer
    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

6.3.3 Soft Start and Prebiased Soft Start

The TPSM8663x has an adjustable soft-start time that can be set by connecting a capacitor between SS and AGND. When the EN pin becomes high, the soft-start charge current (ISS) begins charging the external capacitor (CSS) connected between SS and AGND. Equation 2 calculates the soft-start time (TSS) :

Equation 2. Tss = Css×VREFISS

If the external capacitor (CSS) has pre-stored voltage at start-up, the device initially discharges the external capacitor voltage to lower voltage then charge again to prevent inrush start-up.

If the output capacitor is prebiased at start-up, the device initiates switching and starts ramping up only after the internal reference voltage becomes greater than the feedback voltage VFB. This scheme makes sure that the converters ramp up smoothly into regulation point.