ZHCSH33Z September   1997  – April 2025 LM317

PRODUCTION DATA  

  1.   1
  2. 1 特性
  3. 2 应用
  4. 3 说明
  5. 4 Device Comparison Table
  6. 5 Pin Configuration and Functions
  7. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information (Legacy Chip)
    5. 6.5 Thermal Information (New Chip)
    6. 6.6 Electrical Characteristics
    7. 6.7 Typical Characteristics
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 NPN Darlington Output Drive
      2. 7.3.2 Overload Block
      3. 7.3.3 Programmable Feedback
    4. 7.4 Device Functional Modes
      1. 7.4.1 Normal Operation
      2. 7.4.2 Operation With Low Input Voltage
      3. 7.4.3 Operation at Light Loads
      4. 7.4.4 Operation In Self Protection
  9. 8 Application and Implementation
    1. 8.1 Application Information
    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 System Examples
      1. 8.3.1  0V to 30V Regulator Circuit
      2. 8.3.2  Adjustable Regulator Circuit With Improved Ripple Rejection
      3. 8.3.3  Precision Current-Limiter Circuit
      4. 8.3.4  Tracking Preregulator Circuit
      5. 8.3.5  1.25V to 20V Regulator Circuit With Minimum Program Current
      6. 8.3.6  Battery-Charger Circuit
      7. 8.3.7  50mA, Constant-Current, Battery-Charger Circuit
      8. 8.3.8  Slow Turn-On 15V Regulator Circuit
      9. 8.3.9  AC Voltage-Regulator Circuit
      10. 8.3.10 Current-Limited 6V Charger Circuit
      11. 8.3.11 Adjustable 4A Regulator Circuit
      12. 8.3.12 High-Current Adjustable Regulator Circuit
    4. 8.4 Power Supply Recommendations
    5. 8.5 Layout
      1. 8.5.1 Layout Guidelines
        1. 8.5.1.1 Thermal Considerations
          1. 8.5.1.1.1 Heat Sink Requirements
          2. 8.5.1.1.2 Heat Sinking Surface-Mount Packages
            1. 8.5.1.1.2.1 Heatsinking the SOT-223 (DCY) Package
            2. 8.5.1.1.2.2 Heat Sinking the TO-263 (KTT) Package
      2. 8.5.2 Layout Examples
  10. 9 Device and Documentation Support
    1. 9.1 Device Support
      1. 9.1.1 Device Nomenclature
    2. 9.2 接收文档更新通知
    3. 9.3 支持资源
    4. 9.4 Trademarks
    5. 9.5 静电放电警告
    6. 9.6 术语表
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

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8.5.1.1.1 Heat Sink Requirements

The LM317 (new chip) regulators have internal thermal shutdown to protect the device from overheating. Under all operating conditions, make sure the device junction temperature does not exceed the rated maximum junction temperature (TJ) of 125°C for the LM317 (new chip). A heat sink is required depending on the maximum device power dissipation and the maximum ambient temperature of the application. To determine if a heat sink is needed, Equation 9 calculates the power dissipated by the regulator, PD.

Equation 9. PD = ((VIN − VOUT) × IL) + (VIN × IG)

Figure 8-18 shows the voltage and currents that are present in the circuit.

Equation 10 calculates the next parameter, which is the maximum allowable temperature rise, TR(MAX).

Equation 10. TR(MAX) = TJ(MAX) − TA(MAX)

where:

  • TJ(MAX) is the maximum allowable junction temperature (125°C for the LM317, new chip)
  • TA(MAX) is the maximum ambient temperature encountered in the application

Using the calculated values for TR(MAX) and PD, Equation 11 calculates the maximum allowable value for the junction-to-ambient thermal resistance (RθJA).

Equation 11. RθJA = (TR(MAX) / PD)
LM317 Power Dissipation DiagramFigure 8-18 Power Dissipation Diagram

If the calculated maximum allowable thermal resistance is higher than the actual package rating, then no additional work is needed. If the calculated maximum allowable thermal resistance is lower than the actual package rating, correct this issue. Either reduce PD or TA(MAX), or lower RθJA by adding a heat sink, or some combination thereof. PD is the device power dissipation, TA(MAX) is the maximum ambient temperature, and RθJA is the device thermal resistance.

Equation 12 calculates the value if a heat sink is needed.

Equation 12. θHA ≤ (RθJA – (θCH + RθJC))

where:

  • θCH is the thermal resistance of the contact area between the device case and the heat sink surface
  • RθJC is thermal resistance from the junction of the die to the surface of the package case

When a value for θHA is calculated, select a heat sink with a value that is less than, or equal to, this number.

The θHA rating is specified numerically by the heat sink manufacturer in the catalog, or given in a curve plotting temperature rise versus power dissipation for the heat sink.