SLVSFC9C October   2020  – May 2026 TPS25947

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison Table
  6. 5 Pin Configuration and Functions
  7. 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 Timing Requirements
    7. 6.7 Switching Characteristics
    8. 6.8 Typical Characteristics
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Input Reverse Polarity Protection
      2. 7.3.2  Undervoltage Lockout (UVLO and UVP)
      3. 7.3.3  Overvoltage Lockout (OVLO)
      4. 7.3.4  Overvoltage Clamp (OVC)
      5. 7.3.5  Inrush Current, Overcurrent, and Short Circuit Protection
        1. 7.3.5.1 Slew Rate (dVdt) and Inrush Current Control
        2. 7.3.5.2 Circuit-Breaker
        3. 7.3.5.3 Active Current Limiting
        4. 7.3.5.4 Short-Circuit Protection
      6. 7.3.6  Analog Load Current Monitor
      7. 7.3.7  Reverse Current Protection
      8. 7.3.8  Overtemperature Protection (OTP)
      9. 7.3.9  Fault Response and Indication (FLT)
      10. 7.3.10 Auxiliary Channel Control (AUXOFF)
      11. 7.3.11 Power Good Indication (PG)
    4. 7.4 Device Functional Modes
  9. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Single Device, Self-Controlled
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Device Selection
        2. 8.2.2.2 Setting Undervoltage and Overvoltage Thresholds
        3. 8.2.2.3 Setting Output Voltage Rise Time (tR)
        4. 8.2.2.4 Setting Power Good Assertion Threshold
        5. 8.2.2.5 Setting Overcurrent Threshold (ILIM)
        6. 8.2.2.6 Setting Overcurrent Blanking Interval (tITIMER)
      3. 8.2.3 Application Curves
      4. 8.2.4 Active ORing
      5. 8.2.5 Priority Power MUXing
      6. 8.2.6 USB PD Port Protection
      7. 8.2.7 Parallel Operation
    3. 8.3 Power Supply Recommendations
      1. 8.3.1 Transient Protection
      2. 8.3.2 Output Short-Circuit Measurements
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Documentation Support
      1. 9.1.1 Related Documentation
    2. 9.2 Receiving Notification of Documentation Updates
    3. 9.3 Support Resources
    4. 9.4 Trademarks
    5. 9.5 Electrostatic Discharge Caution
    6. 9.6 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

8.2.2.3 Setting Output Voltage Rise Time (tR)

For a successful design, the junction temperature of device must be kept below the absolute maximum rating during both dynamic (start-up) and steady-state conditions. Dynamic power stresses often are an order of magnitude greater than the static stresses, so it is important to determine the right start-up time and inrush current limit required with system capacitance to avoid thermal shutdown during start-up.

The slew rate (SR) needed to achieve the desired output rise time can be calculated as:

Equation 12. S R V m s = V I N V t R m s = 12 V 20 m s = 0.6 V m s

The CdVdt needed to achieve this slew rate can be calculated as:

Equation 13. C d V d t p F = 2000 S R V m s = 2000 0.6 = 3333 p F

Choose the nearest standard capacitor value as 3300pF.

For this slew rate, the inrush current can be calculated as:

Equation 14. I I N R U S H m A = S R V m s × C O U T μ F = 0.6 × 470 = 282 m A

The average power dissipation inside the part during inrush can be calculated as:

Equation 15. P D I N R U S H W = I I N R U S H A × V I N V 2 = 0.282 × 12 2 = 1.69 W

For the given power dissipation, the thermal shutdown time of the device must be greater than the ramp-up time tR to avoid start-up failure. Figure 8-3 shows the thermal shutdown limit, for 1.69W of power, the shutdown time is more than 10s which is very large as compared to tR = 20ms. Therefore, it is safe to use 20ms as the startup time for this application.

TPS25947 Thermal Shut-Down Plot During Inrush Figure 8-3 Thermal Shut-Down Plot During Inrush