SBVS066S December   2005  – November 2024 TPS74401

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, Shutdown
      2. 6.3.2 Power-Good (VQFN Package Only)
      3. 6.3.3 Internal Current Limit
      4. 6.3.4 Thermal Protection
    4. 6.4 Device Functional Modes
      1. 6.4.1 Normal Operation
      2. 6.4.2 Dropout Operation
      3. 6.4.3 Disabled
    5. 6.5 Programming
      1. 6.5.1 Programmable Soft-Start
      2. 6.5.2 Sequencing Requirements
  8. 7 Application and Implementation
    1. 7.1 Application Information
      1. 7.1.1 Input, Output, and Bias Capacitor Requirements
      2. 7.1.2 Transient Response
      3. 7.1.3 Dropout Voltage
      4. 7.1.4 Output Noise
    2. 7.2 Typical Applications
      1. 7.2.1 Setting the TPS74401
        1. 7.2.1.1 Design Requirements
        2. 7.2.1.2 Detailed Design Procedure
        3. 7.2.1.3 Application Curves
      2. 7.2.2 Using an Auxiliary Bias Rail
      3. 7.2.3 Without an Auxiliary Bias
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
        1. 7.4.1.1 Power Dissipation
        2. 7.4.1.2 Thermal Considerations
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Documentation Support
      1. 8.1.1 Related Documentation
      2. 8.1.2 Device Nomenclature
    2. 8.2 Device Support
      1. 8.2.1 Development Support
        1. 8.2.1.1 Evaluation Modules
        2. 8.2.1.2 Spice Models
    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

7.4.1.1 Power Dissipation

Knowing the device power dissipation and proper sizing of the thermal plane that is connected to the tab or pad is critical to avoiding thermal shutdown and verifying reliable operation.

Power dissipation of the device depends on input voltage and load conditions, and can be calculated using Equation 6:

Equation 6. P D = V I N – V O U T × I O U T

Power dissipation can be minimized and greater efficiency can be achieved by using the lowest possible input voltage necessary to achieve the required output voltage regulation.

On the VQFN (RGW, RGR) packages, the primary conduction path for heat is through the exposed pad to the PCB. The pad can be connected to ground or left floating; however, the pad must attach to an appropriate amount of copper PCB area to verify that the device does not overheat. On the DDPAK (KTW) package, the primary conduction path for heat is through the tab to the PCB. Connect that tab to ground. The maximum junction-to-ambient thermal resistance depends on the maximum ambient temperature, maximum device junction temperature, and power dissipation of the device and can be estimated using Equation 7:

Equation 7. R θ J A = + 125 ° C – T A P D

Knowing the maximum RθJA, the minimum amount of PCB copper area needed for appropriate heat sinking is estimated using Figure 7-14.

TPS74401 θJA versus Board Size
θJA value at board size of 9 in2 (that is, 3 in × 3 in) is a JEDEC standard.
Figure 7-14 θJA versus Board Size

Figure 7-14 shows the variation of θJA as a function of ground plane copper area in the board. Figure 7-14 is intended only as a guideline to demonstrate the affects of heat spreading in the ground plane; do not use Figure 7-14 to estimate actual thermal performance in real application environments.

Note:

When the device is mounted on an application PCB, TI strongly recommends using ΨJT and ΨJB, as explained in the Thermal Information table.