SNVS775L March   2000  – January 2018 LM317L-N

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
    1.     Schematic Diagram
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Rating
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 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 Load Regulation
    4. 7.4 Device Functional Modes
      1. 7.4.1 External Capacitors
      2. 7.4.2 Protection Diodes
      3. 7.4.3 DSBGA Light Sensitivity
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1  1.25-V to 25-V Adjustable Regulator
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
        3. 8.2.1.3 Application Curve
      2. 8.2.2  Digitally-Selected Outputs
      3. 8.2.3  High Gain Amplifier
      4. 8.2.4  Adjustable Current Limiter
      5. 8.2.5  Precision Current Limiter
      6. 8.2.6  Slow Turnon 15-V Regulator
      7. 8.2.7  Adjustable Regulator With Improved Ripple Rejection
      8. 8.2.8  High Stability 10-V Regulator
      9. 8.2.9  Adjustable Regulator With Current Limiter
      10. 8.2.10 0-V to 30-V Regulator
      11. 8.2.11 Regulator With 15-mA Short-Circuit Current
      12. 8.2.12 Power Follower
      13. 8.2.13 Adjusting Multiple On-Card Regulators With Single Control
      14. 8.2.14 100-mA Current Regulator
      15. 8.2.15 1.2-V to 12-V Regulator With Minimum Program Current
      16. 8.2.16 50-mA Constant Current Battery Charger for Nickel-Cadmium Batteries
      17. 8.2.17 5-V Logic Regulator With Electronic Shutdown
      18. 8.2.18 Current-Limited 6-V Charger
      19. 8.2.19 Short Circuit-Protected 80-V Supply
      20. 8.2.20 Basic High-Voltage Regulator
      21. 8.2.21 Precision High-Voltage Regulator
      22. 8.2.22 Tracking Regulator
      23. 8.2.23 Regulator With Trimmable Output Voltage
      24. 8.2.24 Precision Reference With Short-Circuit Proof Output
      25. 8.2.25 Fully-Protected (Bulletproof) Lamp Driver
      26. 8.2.26 Lamp Flasher
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Examples
    3. 10.3 Thermal Considerations
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Community Resources
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

7.4.2 Protection Diodes

When external capacitors are used with any IC regulator it is sometimes necessary to add protection diodes to prevent the capacitors from discharging through low current points into the regulator. Most 10-μF capacitors have low enough internal series resistance to deliver 20-A spikes when shorted. Although the surge is short, there is enough energy to damage parts of the IC.

When an output capacitor is connected to a regulator and the input is shorted, the output capacitor will discharge into the output of the regulator. The discharge current depends on the value of the capacitor, the output voltage of the regulator, and the rate of decrease of VIN. In the LM317L-N, this discharge path is through a large junction that is able to sustain a 2-A surge with no problem. This is not true of other types of positive regulators. For output capacitors of 25 μF or less, the ballast resistors and output structure of the LM317L-N limit the peak current to a low enough level so that there is no need to use a protection diode.

The bypass capacitor on the adjustment terminal can discharge through a low current junction. Discharge occurs when either the input or output is shorted. Internal to the LM317L-N is a 50-Ω resistor which limits the peak discharge current. No protection is needed for output voltages of 25 V or less and 10-μF capacitance. Figure 15 shows an LM317L-N with protection diodes included for use with outputs greater than 25 V and high values of output capacitance.

LM317L-N 906409.png

LM317L-N 906447.png
D1 protects against C1

D2 protects against C2
Figure 15. Regulator With Protection Diodes