JAJS772E June   1999  – July 2018 LM2574 , LM2574HV

PRODUCTION DATA.  

  1. 1 特長
  2. 2 アプリケーション
  3. 3 概要
    1.     Device Images
      1.      代表的なアプリケーション(固定出力電圧版)
  4. 4 改訂履歴
  5. 5 Pin Configuration and Functions
    1.     Pin 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 for All Output Voltage Versions
    6. 6.6  Electrical Characteristics – 3.3-V Version
    7. 6.7  Electrical Characteristics – 5-V Version
    8. 6.8  Electrical Characteristics – 12-V Version
    9. 6.9  Electrical Characteristics – 15-V Version
    10. 6.10 Electrical Characteristics – Adjustable Version
    11. 6.11 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Current Limit
      2. 7.3.2 Undervoltage Lockout
      3. 7.3.3 Delayed Start-Up
      4. 7.3.4 Adjustable Output, Low-Ripple Power Supply
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown Mode
      2. 7.4.2 Active Mode
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Input Capacitor (CIN)
      2. 8.1.2 Inductor Selection
      3. 8.1.3 Inductor Ripple Current
      4. 8.1.4 Output Capacitor
      5. 8.1.5 Catch Diode
      6. 8.1.6 Output Voltage Ripple and Transients
      7. 8.1.7 Feedback Connection
      8. 8.1.8 ON/OFF Input
      9. 8.1.9 Additional Applications
        1. 8.1.9.1 Inverting Regulator
        2. 8.1.9.2 Negative Boost Regulator
    2. 8.2 Typical Applications
      1. 8.2.1 Fixed Output Voltage Applications
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 Custom Design With WEBENCH® Tools
          2. 8.2.1.2.2 Inductor Selection (L1)
          3. 8.2.1.2.3 Output Capacitor Selection (COUT)
          4. 8.2.1.2.4 Catch Diode Selection (D1)
          5. 8.2.1.2.5 Input Capacitor (CIN)
        3. 8.2.1.3 Application Curves
      2. 8.2.2 Adjustable Output Voltage Applications
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
          1. 8.2.2.2.1 Programming Output Voltage
          2. 8.2.2.2.2 Inductor Selection (L1)
          3. 8.2.2.2.3 Output Capacitor Selection (COUT)
          4. 8.2.2.2.4 Catch Diode Selection (D1)
          5. 8.2.2.2.5 Input Capacitor (CIN)
        3. 8.2.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 Grounding
    4. 10.4 Thermal Considerations
  11. 11デバイスおよびドキュメントのサポート
    1. 11.1 デバイス・サポート
      1. 11.1.1 デベロッパー・ネットワークの製品に関する免責事項
      2. 11.1.2 WEBENCH®ツールによるカスタム設計
      3. 11.1.3 デバイスの項目表記
        1. 11.1.3.1  降圧レギュレータ
        2. 11.1.3.2  昇降圧レギュレータ
        3. 11.1.3.3  デューティ・サイクル(D)
        4. 11.1.3.4  キャッチ・ダイオードまたは電流ステアリング・ダイオード
        5. 11.1.3.5  コンデンサの等価直列抵抗(ESR)
        6. 11.1.3.6  等価直列インダクタンス(ESL)
        7. 11.1.3.7  出力リップル電圧
        8. 11.1.3.8  コンデンサのリップル電流
        9. 11.1.3.9  スタンバイ時静止電流(ISTBY)
        10. 11.1.3.10 インダクタのリップル電流(ΔIIND)
        11. 11.1.3.11 連続/不連続モードの動作
        12. 11.1.3.12 インダクタの飽和
        13. 11.1.3.13 動作電圧のマイクロ秒定数(E・Top)
    2. 11.2 ドキュメントのサポート
      1. 11.2.1 関連資料
    3. 11.3 ドキュメントの更新通知を受け取る方法
    4. 11.4 コミュニティ・リソース
    5. 11.5 商標
    6. 11.6 静電気放電に関する注意事項
    7. 11.7 Glossary
  12. 12メカニカル、パッケージ、および注文情報

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

10.4 Thermal Considerations

The 8-pin PDIP (P) package and the 14-pin SOIC (NPA) package are molded plastic packages with solid copper lead frames. The copper lead frame conducts the majority of the heat from the die, through the leads, to the printed-circuit board copper, which acts as the heat sink. For best thermal performance, wide copper traces must be used, and all ground and unused pins must be soldered to generous amounts of printed-circuit board copper, such as a ground plane. Large areas of copper provide the best transfer of heat (lower thermal resistance) to the surrounding air, and even double-sided or multilayer boards provide better heat paths to the surrounding air. Unless the power levels are small, using a socket for the 8-pin package is not recommended because of the additional thermal resistance it introduces, and the resultant higher junction temperature.

Because of the 0.5-A current rating of the LM2574, the total package power dissipation for this switcher is quite low, ranging from approximately 0.1 W up to 0.75 W under varying conditions. In a carefully engineered printed-circuit board, both the P and the NPA package can easily dissipate up to 0.75 W, even at ambient temperatures of 60°C, and still keep the maximum junction temperature less than 125°C.

A curve, Figure 14, displaying thermal resistance versus PCB area for the two packages is shown in Typical Characteristics.

These thermal resistance numbers are approximate, and there can be many factors that affect the final thermal resistance. Some of these factors include board size, shape, thickness, position, location, and board temperature. Other factors are, the area of printed-circuit copper, copper thickness, trace width, multi-layer, single- or double-sided, and the amount of solder on the board. The effectiveness of the PCB to dissipate heat also depends on the size, number and spacing of other components on the board. Furthermore, some of these components, such as the catch diode and inductor generate some additional heat. Also, the thermal resistance decreases as the power level increases because of the increased air current activity at the higher power levels, and the lower surface to air resistance coefficient at higher temperatures.

The data sheet thermal resistance curves can estimate the maximum junction temperature based on operating conditions. ln addition, the junction temperature can be estimated in actual circuit operation by using Equation 15.

Equation 15. Tj = Tcu + (θj-cu × PD)

With the switcher operating under worst case conditions and all other components on the board in the intended enclosure, measure the copper temperature (Tcu ) near the IC. This can be done by temporarily soldering a small thermocouple to the PCB copper near the IC, or by holding a small thermocouple on the PCB copper using thermal grease for good thermal conduction.

The thermal resistance (θj-cu) for the two packages is:

θj-cu = 42°C/W for the P-8 package

θj-cu = 52°C/W for the NPA-14 package

The power dissipation (PD) for the IC could be measured, or it can be estimated by using Equation 16.

Equation 16. LM2574 LM2574HV eq_pd_snvs104.gif

where

  • IS is obtained from the typical supply current curve (adjustable version use the supply current vs duty cycle curve)