SLUSDX1A September   2020  – August 2021 TPS563211

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 Advanced Emulated Current Mode Control
      2. 7.3.2 Mode Selection and PG/SS Pin Function Configuration
      3. 7.3.3 Power Good (PG)
      4. 7.3.4 Soft Start and Pre-Biased Soft Start
      5. 7.3.5 Output Discharge through PG/SS Pin
      6. 7.3.6 Precise Enable and Adjusting Undervoltage Lockout
      7. 7.3.7 Overcurrent Limit and Undervoltage Protection
      8. 7.3.8 Overvoltage Protection
      9. 7.3.9 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown Mode
      2. 7.4.2 Active Mode
      3. 7.4.3 CCM Operation
      4. 7.4.4 FCCM Operation
      5. 7.4.5 DCM Operation and Eco-Mode Operation
      6. 7.4.6 On-Time Extension for Large Duty Cycle Operation
  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 Custom Design With WEBENCH® Tools
        2. 8.2.2.2 Output Voltage Resistors Selection
        3. 8.2.2.3 Output Inductor Selection
        4. 8.2.2.4 Output Capacitor Selection
        5. 8.2.2.5 Input Capacitor Selection
        6. 8.2.2.6 Bootstrap Capacitor Selection
        7. 8.2.2.7 Undervoltage Lockout Set Point
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Development Support
        1. 11.1.1.1 Custom Design With WEBENCH® Tools
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Support Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

7.3.4 Soft Start and Pre-Biased Soft Start

This is an optional function configured by MODE pin.

If the PG function is selected, the device works with an internal soft-start time of 2 ms. If the SS function is selected, the device has the adjustable soft-start function. When the EN pin becomes high, the soft-start charge current, ISS, begins charging the capacitor, which is connected from the PG/SS pin to GND (CSS). Smooth control of the output voltage is maintained during start-up. Use Equation 1 to calculate the soft-start time.

Equation 1. tssms=3.5×Css(nF)×VREF(V)Iss(uA)
where
  • VREF = 0.6 V, ISS = 6.6 µA

The value of the external soft-start capacitor must not be lower than 4 nF typical to make sure the user has good start-up behavior.

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