ZHCSN51J june   2007  – april 2023 TPS74901

PRODUCTION DATA  

  1. 1 特性
  2. 2 应用
  3. 3 说明
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 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: Other Orderable Devices (non-M3 Suffix)
    6. 6.6  Electrical Characteristics: Orderable Device (M3 Suffix)
    7. 6.7  Typical Characteristics: IOUT = 50 mA (All Other Orderable Devices, Non-M3 Suffix)
    8. 6.8  Typical Characteristics: IOUT = 1 A (All Other Orderable Devices, Non-M3 Suffix)
    9. 6.9  Typical Characteristics: IOUT = 50 mA (M3 Suffix)
    10. 6.10 Typical Characteristics: IOUT = 1 A (M3 Suffix)
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Enable and Shutdown
      2. 7.3.2 Power-Good
      3. 7.3.3 Internal Current Limit
      4. 7.3.4 Thermal Protection
    4. 7.4 Device Functional Modes
      1. 7.4.1 Normal Operation
      2. 7.4.2 Dropout Operation
      3. 7.4.3 Disabled
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Input, Output, and BIAS Capacitor Requirements
      2. 8.1.2 Transient Response
      3. 8.1.3 Dropout Voltage
      4. 8.1.4 Output Noise
      5. 8.1.5 Programmable Soft-Start
      6. 8.1.6 Sequencing Requirements
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
      3. 8.2.3 Application Curves
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
        1. 8.4.1.1 Power Dissipation
        2. 8.4.1.2 Thermal Considerations
      2. 8.4.2 Layout Example
  9. 9 Device and Documentation Support
    1. 9.1 Device Support
      1. 9.1.1 Development Support
        1. 9.1.1.1 Evaluation Modules
        2. 9.1.1.2 Spice Models
    2. 9.2 Documentation Support
      1. 9.2.1 Related Documentation
    3. 9.3 接收文档更新通知
    4. 9.4 支持资源
    5. 9.5 Trademarks
    6. 9.6 静电放电警告
    7. 9.7 术语表
  10. 10Mechanical, Packaging, and Orderable Information

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机械数据 (封装 | 引脚)
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订购信息

8.4.1.2 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. GUID-DA650505-F492-4806-9E0F-5D59BED771A0-low.gif

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 1 mm away from the device package on the PCB surface (see Figure 8-8)

 

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.

GUID-63F6DEF7-C8E1-4A38-89FE-D9976E298FEE-low.gif
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 8-8 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 8-9 shows characteristic performance of ΨJT and ΨJB versus board size.

Referring to Figure 8-9, 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 8-8), 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.

GUID-9E8668F2-BB5F-4481-B049-EAF3054683E1-low.gifFigure 8-9 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.