SLVS348N July   2001  – January 2025 TPS793

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 Diagrams
    3. 6.3 Feature Description
      1. 6.3.1 Undervoltage Lockout (UVLO)
      2. 6.3.2 Shutdown
      3. 6.3.3 Active Discharge (new chip)
      4. 6.3.4 Foldback Current Limit
      5. 6.3.5 Thermal Protection
      6. 6.3.6 Reverse Current
    4. 6.4 Device Functional Modes
      1. 6.4.1 Normal Operation
      2. 6.4.2 Dropout Operation
      3. 6.4.3 Disabled
  8. 7 Application and Implementation
    1. 7.1 Application Information
      1. 7.1.1 Adjustable Operation
      2. 7.1.2 Exiting Dropout
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
        1. 7.2.2.1 Capacitor Recommendations
        2. 7.2.2.2 Input and Output Capacitor Requirements
        3. 7.2.2.3 Noise Reduction and Feed-Forward Capacitor Requirements
      3. 7.2.3 Application Curves
    3. 7.3 Best Design Practices
    4. 7.4 Power Supply Recommendations
    5. 7.5 Layout
      1. 7.5.1 Layout Guidelines
        1. 7.5.1.1 Board Layout Recommendations to Improve PSRR and Noise Performance
        2. 7.5.1.2 Power Dissipation
      2. 7.5.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Development Support
        1. 8.1.1.1 Evaluation Modules
        2. 8.1.1.2 Spice Models
      2. 8.1.2 Device Nomenclature
    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

7.5.1.2 Power Dissipation

The ability to remove heat from the die is different for each package type, presenting different considerations in the printed circuit board (PCB) layout. The PCB area around the device that is free of other components moves the heat from the device to the ambient air. Performance data for JEDEC low- and high-K boards are given in the Thermal Information table. Using heavier copper increases the effectiveness in removing heat from the device. The addition of plated through-holes to heat-dissipating layers also improves the heatsink effectiveness.

Power dissipation depends on input voltage and load conditions. Power dissipation (PD) can be approximated by the product of the output current times the voltage drop across the output pass element (VIN to VOUT), as shown in Equation 4.

Where:

  • TJmax is the maximum allowable junction temperature.
  • RθJA is the thermal resistance junction-to-ambient for the package.
  • TA is the ambient temperature.
Equation 4. TPS793

Power dissipation resulting from quiescent current is negligible. Excessive power dissipation triggers the thermal protection circuit.

Figure 7-8 shows the maximum ambient temperature versus the power dissipation of the TPS730. This figure assumes the device is soldered on a JEDEC standard, high-K layout with no airflow over the board. Actual board thermal impedances vary widely. If the application requires high power dissipation, having a thorough understanding of the board temperature and thermal impedances is helpful to verify the TPS730 does not operate above a junction temperature of 125°C.

TPS793 Maximum Ambient Temperature vs Power DissipationFigure 7-8 Maximum Ambient Temperature vs Power Dissipation

Estimating the junction temperature can be done by using the thermal metrics ΨJT and ΨJB, shown in the Thermal Information table. These metrics are a more accurate representation of the heat transfer characteristics of the die and the package than RθJA. The junction temperature can be estimated with Equation 5.

 

Equation 5. TPS793

where

  • PD is the power dissipation shown by Equation 4.
  • TT is the temperature at the center-top of the IC package.
  • TB is the PCB temperature measured 1 mm away from the IC package on the PCB surface.
Note:

Both TT and TB can be measured on actual application boards using a thermo‐gun (an infrared thermometer).

For more information about measuring TT and TB, see the application note Using New Thermal Metrics (SBVA025), available for download at www.ti.com.