Datasheet LM340, LM340A, LM7805, LM7812, LM7815 (Texas Instruments) - 13

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LM340 , LM340A , LM7805 , LM7812, LM7815 www.ti.com
SNOSBT0L – FEBRUARY 2000 – REVISED SEPTEMBER 2016
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.
Figure 15. Input Short
Copyright © 2000–2016, Texas Instruments Incorporated Submit Documentation Feedback 13 Product Folder Links: LM340 LM340A LM7805 LM7812 LM7815 Document Outline 1 Features 2 Applications 3 Description Table of Contents 4 Revision History 5 Pin Configuration and Functions 6 Specifications 6.1 Absolute Maximum Ratings 6.2 ESD Ratings 6.3 Recommended Operating Conditions 6.4 Thermal Information 6.5 LM340A Electrical Characteristics, VO = 5 V, VI = 10 V 6.6 LM340 / LM7805 Electrical Characteristics, VO = 5 V, VI = 10 V 6.7 LM340 / LM7812 Electrical Characteristics, VO = 12 V, VI = 19 V 6.8 LM340 / LM7815 Electrical Characteristics, VO = 15 V, VI = 23 V 6.9 Typical Characteristics 7 Detailed Description 7.1 Overview 7.2 Functional Block Diagram 7.3 Feature Description 7.3.1 Output Current 7.3.2 Current Limiting Feature 7.3.3 Thermal Shutdown 7.4 Device Functional Modes 8 Application and Implementation 8.1 Application Information 8.1.1 Shorting the Regulator Input 8.1.2 Raising the Output Voltage Above the Input Voltage 8.1.3 Regulator Floating Ground 8.1.4 Transient Voltages 8.2 Typical Applications 8.2.1 Fixed Output Voltage Regulator 8.2.1.1 Design Requirements 8.2.1.2 Detailed Design Procedure 8.2.1.3 Application Curve 8.3 System Examples 9 Power Supply Recommendations 10 Layout 10.1 Layout Guidelines 10.2 Layout Example 10.3 Heat Sinking DDPAK/TO-263 and SOT-223 Package Parts 11 Device and Documentation Support 11.1 Documentation Support 11.1.1 Related Documentation 11.2 Related Links 11.3 Receiving Notification of Documentation Updates 11.4 Community Resources 11.5 Trademarks 11.6 Electrostatic Discharge Caution 11.7 Glossary 12 Mechanical, Packaging, and Orderable Information Page 1