SNOSBT0L February   2000  – September 2016 LM340

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
    1.     Available Packages
  3. 3 Description
    1.     Fixed Output Voltage Regulator
  4. 4 Revision History
  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 LM340A Electrical Characteristics, VO = 5 V, VI = 10 V
    6. 6.6 LM340 / LM7805 Electrical Characteristics, VO = 5 V, VI = 10 V
    7. 6.7 LM340 / LM7812 Electrical Characteristics, VO = 12 V, VI = 19 V
    8. 6.8 LM340 / LM7815 Electrical Characteristics, VO = 15 V, VI = 23 V
    9. 6.9 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 Output Current
      2. 7.3.2 Current Limiting Feature
      3. 7.3.3 Thermal Shutdown
    4. 7.4 Device Functional Modes
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Shorting the Regulator Input
      2. 8.1.2 Raising the Output Voltage Above the Input Voltage
      3. 8.1.3 Regulator Floating Ground
      4. 8.1.4 Transient Voltages
    2. 8.2 Typical Applications
      1. 8.2.1 Fixed Output Voltage Regulator
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
        3. 8.2.1.3 Application Curve
    3. 8.3 System Examples
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 Heat Sinking DDPAK/TO-263 and SOT-223 Package Parts
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Related Links
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 Community Resources
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

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発注情報

8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.

8.1 Application Information

The LM340x and LM7805 series is designed with thermal protection, output short-circuit protection, and output transistor safe area protection. However, as with any IC regulator, it becomes necessary to take precautions to assure that the regulator is not inadvertently damaged. The following describes possible misapplications and methods to prevent damage to the regulator.

8.1.1 Shorting the Regulator Input

When using large capacitors at the output of these regulators, a protection diode connected input to output (Figure 15) may be required if the input is shorted to ground. Without the protection diode, an input short causes the input to rapidly approach ground potential, while the output remains near the initial VOUT because of the stored charge in the large output capacitor. The capacitor will then discharge through a large internal input to output diode and parasitic transistors. If the energy released by the capacitor is large enough, this diode, low current metal, and the regulator are destroyed. The fast diode in Figure 15 shunts most of the capacitors discharge current around the regulator. Generally no protection diode is required for values of output capacitance ≤ 10 μF.

8.1.2 Raising the Output Voltage Above the Input Voltage

Because the output of the device does not sink current, forcing the output high can cause damage to internal low current paths in a manner similar to that just described in Shorting the Regulator Input.

8.1.3 Regulator Floating Ground

When the ground pin alone becomes disconnected, the output approaches the unregulated input, causing possible damage to other circuits connected to VOUT. If ground is reconnected with power ON, damage may also occur to the regulator. This fault is most likely to occur when plugging in regulators or modules with on card regulators into powered up sockets. The power must be turned off first, the thermal limit ceases operating, or the ground must be connected first if power must be left on. See Figure 16.

8.1.4 Transient Voltages

If transients exceed the maximum rated input voltage of the device, or reach more than 0.8 V below ground and have sufficient energy, they will damage the regulator. The solution is to use a large input capacitor, a series input breakdown diode, a choke, a transient suppressor or a combination of these.

LM340 LM340A LM7805 LM7812 LM7815 00778108.png Figure 15. Input Short
LM340 LM340A LM7805 LM7812 LM7815 00778109.png Figure 16. Regulator Floating Ground
LM340 LM340A LM7805 LM7812 LM7815 00778110.png Figure 17. Transients

When a value for θ(H–A) is found, a heat sink must be selected that has a value that is less than or equal to this number.

θ(H–A) is specified numerically by the heat sink manufacturer in this catalog or shown in a curve that plots temperature rise vs power dissipation for the heat sink.

8.2 Typical Applications

8.2.1 Fixed Output Voltage Regulator

The LM340x and LM7805 Family devices are primarily designed to provide fixed output voltage regulation. The simplest implementation of LM340x and LM7805 Family is shown in Figure 18.

LM340 LM340A LM7805 LM7812 LM7815 00778101.png
*Required if the regulator is located far from the power supply filter.
**Although no output capacitor is needed for stability, it does help transient response. (If needed, use 0.1-μF, ceramic disc).
Figure 18. Fixed Output Voltage Regulator

8.2.1.1 Design Requirements

The device component count is very minimal. Although not required, TI recommends employing bypass capacitors at the output for optimum stability and transient response. These capacitors must be placed as close as possible to the regulator. If the device is located more than 6 inches from the power supply filter, it is required to employ input capacitor.

8.2.1.2 Detailed Design Procedure

The output voltage is set based on the device variant. LM340x and LM7805 Family are available in 5-V, 12-V and 15-V regulator options.

8.2.1.3 Application Curve

LM340 LM340A LM7805 LM7812 LM7815 00778129.png Figure 19. VOUT vs VIN, VOUT = 5 V

8.3 System Examples

LM340 LM340A LM7805 LM7812 LM7815 00778103_1.png
IOUT = V2–3 / R1 + IQ
ΔIQ = 1.3 mA over line and load changes.
Figure 20. Current Regulator
LM340 LM340A LM7805 LM7812 LM7815 00778102.png
VOUT = 5 V + (5 V/R1 + IQ) R2 5 V/R1 > 3 IQ,
load regulation (Lr) ≈ [(R1 + R2)/R1] (Lr of LM340-5).
Figure 21. Adjustable Output Regulator
LM340 LM340A LM7805 LM7812 LM7815 00778114.gif Figure 22. High Input Voltage Circuit With Series Resistor
LM340 LM340A LM7805 LM7812 LM7815 00778116.gif
β(Q1) ≥ IO Max / IREG Max
R1 = 0.9 / IREG = β(Q1) VBE(Q1) / IREG Max (β +1) – IO Max
Figure 24. High Current Voltage Regulator
LM340 LM340A LM7805 LM7812 LM7815 00778118.gif Figure 26. LM340 Used With Negative Regulator LM79xx
LM340 LM340A LM7805 LM7812 LM7815 00778115.gif Figure 23. High Input Voltage Circuit implementation With Transistor
LM340 LM340A LM7805 LM7812 LM7815 00778117.gif
RSC = 0.8 / ISC
R1 = βVBE(Q1) / IREG Max (β +1) – IO Max
Figure 25. High Output Current With Short-Circuit Protection