SLVSFQ0B October   2020  – June 2024 TPS54J061

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  Enable and Internal LDO
      2. 6.3.2  Split Rail and External LDO
      3. 6.3.3  Output Voltage Setting
      4. 6.3.4  Soft Start and Output-Voltage Tracking
      5. 6.3.5  Frequency and Operation Mode Selection
      6. 6.3.6  D-CAP3™ Control Mode
      7. 6.3.7  Current Sense and Positive Overcurrent Protection
      8. 6.3.8  Low-side FET Negative Current Limit
      9. 6.3.9  Power Good
      10. 6.3.10 Overvoltage and Undervoltage Protection
      11. 6.3.11 Out-Of-Bounds Operation (OOB)
      12. 6.3.12 Output Voltage Discharge
      13. 6.3.13 UVLO Protection
      14. 6.3.14 Thermal Shutdown
    4. 6.4 Device Functional Modes
      1. 6.4.1 Auto-Skip Eco-Mode Light Load Operation
      2. 6.4.2 Forced Continuous-Conduction Mode
      3. 6.4.3 Pre-Bias Start-up
  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  Choose the Switching Frequency and Operation Mode (MODE Pin)
        2. 7.2.2.2  Choose the Output Inductor (L)
        3. 7.2.2.3  Set the Current Limit (TRIP)
        4. 7.2.2.4  Choose the Output Capacitors (COUT)
        5. 7.2.2.5  Choose the Input Capacitors (CIN)
        6. 7.2.2.6  Feedback Network (FB Pin)
        7. 7.2.2.7  Soft Start Capacitor (SS/REFIN Pin)
        8. 7.2.2.8  EN Pin Resistor Divider
        9. 7.2.2.9  VCC Bypass Capacitor
        10. 7.2.2.10 BOOT Capacitor
        11. 7.2.2.11 Series BOOT Resistor and RC Snubber
        12. 7.2.2.12 PGOOD Pullup Resistor
      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 Example
  9. 8 Device and Documentation Support
    1. 8.1 Documentation Support
      1. 8.1.1 Related Documentation
    2. 8.2 Support Resources
    3. 8.3 Receiving Notification of Documentation Updates
    4. 8.4 Trademarks
    5. 8.5 Glossary
    6. 8.6 Electrostatic Discharge Caution
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Ordering Information

6.3.4 Soft Start and Output-Voltage Tracking

The TPS54J061 implements a circuit to allow both internal fixed soft start and external adjustable soft start. The internal soft-start time is typically 1.5 ms and has a 1-ms minimum value. The internal soft-start time can be increased by adding a SS capacitor between SS/REFIN and AGND. The SS capacitor value can be determined by Equation 2. Note, any CSS calculation that uses a soft-start time of less than 1.5 ms will be ignored by the internal soft-start time circuit. Therefore, selecting a capacitor less than or equal to 22 nF will result in the internal default 1.5 ms soft-start time (Section 7.2.2.7).

Equation 2. TPS54J061

The SS/REFIN pin can also be used as an analog input to accept an external reference. When an external voltage signal is applied to SS/REFIN pin, it acts as the reference voltage, thus FB voltage follows this external voltage signal. Apply the external reference to the SS/REFIN pin before soft start. The external reference voltage must be equal to or higher than the internal reference level to ensure correct Power Good thresholds during soft start. With an external reference applied, the internal fixed soft start controls output voltage ramp during start-up.

After soft start, the external reference voltage signal can be in a range of 0.5 V to 1.2 V.

When driving the SS/REFIN pin with an external resistor divider, the resistance must be low enough so that the external voltage source can overdrive the internal current source. Note that the internal current source remains active.

When the TPS54J061 is enabled, an internal discharge resistance turns on to discharge external capacitance on the SS/REFIN pin and ensure soft-start from 0 V. When the device is enabled with both VIN and EN above the rising thresholds, 100 Ω of resistance is connected from the SS/REFIN pin to ground. After the device detects the VCC pin is in regulation, the discharge resistance is increased to 300 Ω. The 300-Ω discharge resistance is connected to the SS/REFIN until the MODE detection time is completed. After the MODE detection time is completed, the TPS54J061 detects if an external reference is connected.