SLVSE52A September   2018  – November 2018 TPS61088-Q1

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Typical Application Circuit
  4. 4 Revision History
  5. 5 Description (continued)
  6. 6 Pin Configuration and Functions
    1.     Pin Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 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 Enable and Start-up
      2. 8.3.2 Undervoltage Lockout (UVLO)
      3. 8.3.3 Adjustable Switching Frequency
      4. 8.3.4 Adjustable Peak Current Limit
      5. 8.3.5 Overvoltage Protection
      6. 8.3.6 Thermal Shutdown
    4. 8.4 Device Functional Modes
      1. 8.4.1 Operation
        1. 8.4.1.1 PWM Mode
        2. 8.4.1.2 PFM Mode
  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 Custom Design with WEBENCH Tools
        2. 9.2.2.2 Setting Switching Frequency
        3. 9.2.2.3 Setting Peak Current Limit
        4. 9.2.2.4 Setting Output Voltage
        5. 9.2.2.5 Inductor Selection
        6. 9.2.2.6 Input Capacitor Selection
        7. 9.2.2.7 Output Capacitor Selection
        8. 9.2.2.8 Loop Stability
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
    3. 11.3 Thermal Considerations
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Third-Party Products Disclaimer
      2. 12.1.2 Development Support
        1. 12.1.2.1 Custom Design with WEBENCH Tools
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Community Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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

8.3.1 Enable and Start-up

The TPS61088-Q1 has an adjustable soft-start function to prevent high inrush current during start-up. To minimize the inrush current during start-up, an external capacitor, connected to the SS pin and charged with a constant current, is used to slowly ramp up the internal positive input of the error amplifier. When the EN pin is pulled high, the soft-start capacitor CSS (C7 in the Functional Block Diagram) is charged with a constant current of 5 μA typically. During this time, the SS pin voltage is compared with the internal reference (1.204 V), the lower one is fed into the internal positive input of the error amplifier. The output of the error amplifier (which determines the inductor peak current value) ramps up slowly as the SS pin voltage goes up. The soft-start phase is completed after the SS pin voltage exceeds the internal reference (1.204 V). The larger the capacitance at the SS pin, the slower the ramp of the output voltage and the longer the soft-start time. A 47-nF capacitor is usually sufficient for most applications. When the EN pin is pulled low, the voltage of the soft-start capacitor is discharged to ground.

Use Equation 1 to calculate the soft-start time.

Equation 1. TPS61088-Q1 eq_soft_start_1_LVSCW6.gif

where

  • tSS is the soft-start time.
  • VREF is the internal reference voltage of 1.204 V.
  • CSS is the capacitance between the SS pin and ground.
  • ISS is the soft-start charging current of 5 µA.