JAJSFY4C August   2018  – October 2019 LMR36015-Q1

PRODUCTION DATA.  

  1. 1 特長
  2. 2 アプリケーション
  3. 3 概要
    1.     Device Images
      1.      概略回路図
  4. 4 改訂履歴
  5. 5 概要（続き）
  6. 6 Device Comparison Table
  7. 7 Pin Configuration and Functions
    1.     Pin Functions
  8. 8 Specifications
    1. 8.1 Absolute Maximum Ratings
    2. 8.2 ESD Ratings
    3. 8.3 Recommended Operating Conditions
    4. 8.4 Thermal Information
    5. 8.5 Electrical Characteristics
    6. 8.6 Timing Requirements
    7. 8.7 System Characteristics
    8. 8.8 Typical Characteristics
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Power-Good Flag Output
      2. 9.3.2 Enable and Start-up
      3. 9.3.3 Current Limit and Short Circuit
      4. 9.3.4 Undervoltage Lockout and Thermal Shutdown
    4. 9.4 Device Functional Modes
      1. 9.4.1 Auto Mode
      2. 9.4.2 Forced PWM Operation
      3. 9.4.3 Dropout
      4. 9.4.4 Minimum Switch On-Time
      5. 9.4.5 Spread Spectrum Operation
  10. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Application
      1. 10.2.1 Design 1: Low Power 24-V, 1.5-A PFM Converter
        1. 10.2.1.1 Design Requirements
        2. 10.2.1.2 Detailed Design Procedure
          1. 10.2.1.2.1  Custom Design With WEBENCH Tools
          2. 10.2.1.2.2  Choosing the Switching Frequency
          3. 10.2.1.2.3  Setting the Output Voltage
            1. 10.2.1.2.3.1 FB for Adjustable Output
          4. 10.2.1.2.4  Inductor Selection
          5. 10.2.1.2.5  Output Capacitor Selection
          6. 10.2.1.2.6  Input Capacitor Selection
          7. 10.2.1.2.7  CBOOT
          8. 10.2.1.2.8  VCC
          9. 10.2.1.2.9  CFF Selection
            1. 10.2.1.2.9.1 External UVLO
          10. 10.2.1.2.10 Maximum Ambient Temperature
      2. 10.2.2 Application Curves
      3. 10.2.3 Design 2: High Density 12-V, 1.5-A FPWM Converter
        1. 10.2.3.1 Design Requirements
        2. 10.2.3.2 Detailed Design Procedure
        3. 10.2.3.3 Application Curves
    3. 10.3 What to Do and What Not to Do
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
      1. 12.1.1 Ground and Thermal Considerations
    2. 12.2 Layout Example
  13. 13デバイスおよびドキュメントのサポート
    1. 13.1 デバイス・サポート
      1. 13.1.1 開発サポート
        1. 13.1.1.1 WEBENCH®ツールによるカスタム設計
    2. 13.2 ドキュメントのサポート
      1. 13.2.1 関連資料
    3. 13.3 ドキュメントの更新通知を受け取る方法
    4. 13.4 サポート・リソース
    5. 13.5 商標
    6. 13.6 静電気放電に関する注意事項
    7. 13.7 Glossary
  14. 14メカニカル、パッケージ、および注文情報

10.2.1.2.10 Maximum Ambient Temperature

As with any power conversion device, the LMR36015-Q1 dissipates internal power while operating. The effect of this power dissipation is to raise the internal temperature of the converter above ambient. The internal die temperature (TJ) is a function of the ambient temperature, the power loss and the effective thermal resistance, RθJA of the device and PCB combination. The maximum internal die temperature for the LMR36015-Q1 must be limited to 150°C. This establishes a limit on the maximum device power dissipation and therefore the load current. Equation 11 shows the relationships between the important parameters. It is easy to see that larger ambient temperatures (TA) and larger values of RθJA reduce the maximum available output current. The converter efficiency can be estimated by using the curves provided in this data sheet. If the desired operating conditions cannot be found in one of the curves, then interpolation can be used to estimate the efficiency. Alternatively, the EVM can be adjusted to match the desired application requirements and the efficiency can be measured directly. The correct value of RθJA is more difficult to estimate. As stated in Semiconductor and IC Package Thermal Metrics, the values given in are not valid for design purposes and must not be used to estimate the thermal performance of the application. The values reported in that table were measured under a specific set of conditions that are rarely obtained in an actual application.

Equation 11. LMR36015-Q1 TJmax_eq2.gif

where

  • η = Efficiency

The effective RθJA is a critical parameter and depends on many factors such as power dissipation, air temperature/flow, PCB area, copper heat-sink area, number of thermal vias under the package, and adjacent component placement; to mention just a few. Due to the ultra-miniature size of the VQFN (RNX) package, a DAP is not available. This means that this package exhibits a somewhat greater RθJA.A typical example of RθJA vs copper board area can be found in Figure 21. Note that the data given in this graph is for illustration purposes only, and the actual performance in any given application depends on all of the factors mentioned above.

LMR36015-Q1 JA_curve_wson_4L_SNVSAN3.pngFigure 21. RθJA versus Copper Board Area for the VQFN (RNX) Package

Use the following resources as guides to optimal thermal PCB design and estimating RθJA for a given application environment: