JAJS247K June   2007  – June 2024 TPS74901

PRODUCTION DATA  

  1.   1
  2. 1 特長
  3. 2 アプリケーション
  4. 3 概要
  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: IOUT = 50mA
    7. 5.7 Typical Characteristics: IOUT = 1 A
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagrams
    3. 6.3 Feature Description
      1. 6.3.1 Enable and Shutdown
      2. 6.3.2 Power-Good
      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
  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
      5. 7.1.5 Programmable Soft-Start
      6. 7.1.6 Sequencing Requirements
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
      3. 7.2.3 Application Curves
    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 Device Support
      1. 8.1.1 Device Nomenclature
      2. 8.1.2 Development Support
        1. 8.1.2.1 Evaluation Modules
        2. 8.1.2.2 Spice Models
    2. 8.2 Documentation Support
      1. 8.2.1 Related Documentation
    3. 8.3 ドキュメントの更新通知を受け取る方法
    4. 8.4 サポート・リソース
    5. 8.5 Trademarks
    6. 8.6 静電気放電に関する注意事項
    7. 8.7 用語集
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

パッケージ・オプション

メカニカル・データ（パッケージ｜ピン）
サーマルパッド・メカニカル・データ
発注情報

7.4.1.2 Thermal Considerations

A better method of estimating the thermal measure comes from using the thermal metrics ΨJT and ΨJB, as shown in Equation 6. 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 the corresponding formulas given in Equation 6.

Equation 6. TPS74901

where:

  • PD is the power dissipation shown by Equation 4
  • TT is the temperature at the center-top of the device package
  • TB is the PCB temperature measured 1mm away from the device package on the PCB surface (see Figure 7-8)

 

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 Using New Thermal Metrics application note, available for download at www.ti.com.

TPS74901 Measuring Points for TT and TB
A. TT is measured at the center of both the X- and Y-dimensional axes.
B. TB is measured below the package lead on the PCB surface.
Figure 7-8 Measuring Points for TT and TB

Compared with RθJA, the thermal metrics ΨJT and ΨJB are less independent of board size but do have a small dependency on board size and layout. Figure 7-9 shows characteristic performance of ΨJT and ΨJB versus board size.

Referring to Figure 7-9, the RGW package thermal performance has negligible dependency on board size. The KTW package, however, does have a measurable dependency on board size. This dependency exists because the package shape is not point symmetric to the center of a device. In the KTW package, for example (see Figure 7-8), silicon is not beneath the measuring point of TT that is the center of the X and Y dimension, so that ΨJT has a dependency. Also, because of that non-point symmetry, device heat distribution on the PCB is not point symmetric either, so that ΨJB has a greater dependency on board size and layout.

TPS74901 ΨJT and ΨJB versus Board SizeFigure 7-9 ΨJT and ΨJB versus Board Size

For a more detailed discussion of why TI does not recommend using RθJC(top) to determine thermal characteristics, see the Using New Thermal Metrics application note, available for download at www.ti.com. Also, see the IC Package Thermal Metrics application note (also available on the TI website) for further information.