SNVS124E November   1999  – February 2020 LM2596


  1. Features
  2. Applications
  3. Description
    1.     Device Images
      1.      Typical Application
  4. Revision History
  5. Description (continued)
  6. Pin Configuration and Functions
    1.     Pin Functions
  7. Specifications
    1. 7.1  Absolute Maximum Ratings
    2. 7.2  ESD Ratings
    3. 7.3  Operating Conditions
    4. 7.4  Thermal Information
    5. 7.5  Electrical Characteristics – 3.3-V Version
    6. 7.6  Electrical Characteristics – 5-V Version
    7. 7.7  Electrical Characteristics – 12-V Version
    8. 7.8  Electrical Characteristics – Adjustable Voltage Version
    9. 7.9  Electrical Characteristics – All Output Voltage Versions
    10. 7.10 Typical Characteristics
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Delayed Start-Up
      2. 8.3.2 Undervoltage Lockout
      3. 8.3.3 Inverting Regulator
      4. 8.3.4 Inverting Regulator Shutdown Methods
    4. 8.4 Device Functional Modes
      1. 8.4.1 Discontinuous Mode Operation
  9. Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Input Capacitor (CIN)
      2. 9.1.2 Feedforward Capacitor (CFF)
      3. 9.1.3 Output Capacitor (COUT)
      4. 9.1.4 Catch Diode
      5. 9.1.5 Inductor Selection
      6. 9.1.6 Output Voltage Ripple and Transients
      7. 9.1.7 Open-Core Inductors
    2. 9.2 Typical Applications
      1. 9.2.1 LM2596 Fixed Output Series Buck Regulator
        1. Design Requirements
        2. Detailed Design Procedure
          1. Custom Design with WEBENCH Tools
          2. Inductor Selection (L1)
          3. Output Capacitor Selection (COUT)
          4. Catch Diode Selection (D1)
          5. Input Capacitor (CIN)
        3. Application Curves
      2. 9.2.2 LM2596 Adjustable Output Series Buck Regulator
        1. Design Requirements
        2. Detailed Design Procedure
          1. Programming Output Voltage
          2. Inductor Selection (L1)
          3. Output Capacitor Selection (COUT)
          4. Feedforward Capacitor (CFF)
          5. Catch Diode Selection (D1)
          6. Input Capacitor (CIN)
        3. Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Examples
    3. 11.3 Thermal Considerations
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Custom Design with WEBENCH Tools
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Support Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • NDH|5
  • NEB|5
  • KTT|5
Thermal pad, mechanical data (Package|Pins)
Orderable Information

Inductor Selection

All switching regulators have two basic modes of operation; continuous and discontinuous. The difference between the two types relates to the inductor current, whether it is flowing continuously, or if it drops to zero for a period of time in the normal switching cycle. Each mode has distinctively different operating characteristics, which can affect the regulators performance and requirements. Most switcher designs will operate in the discontinuous mode when the load current is low.

The LM2596 (or any of the SIMPLE SWITCHER family) can be used for both continuous or discontinuous modes of operation.

In many cases the preferred mode of operation is the continuous mode, which offers greater output power, lower peak switch, lower inductor and diode currents, and can have lower output ripple voltage. However, the continuous mode does require larger inductor values to keep the inductor current flowing continuously, especially at low output load currents or high input voltages.

To simplify the inductor selection process, an inductor selection guide (nomograph) was designed (see Figure 27 through Figure 30). This guide assumes that the regulator is operating in the continuous mode, and selects an inductor that will allow a peak-to-peak inductor ripple current to be a certain percentage of the maximum design load current. This peak-to-peak inductor ripple current percentage is not fixed, but is allowed to change as different design load currents are selected (see Figure 26.)

LM2596 01258331.pngFigure 26. (ΔIIND) Peak-to-Peak Inductor
Ripple Current (as a Percentage of the Load Current)
versus Load Current

By allowing the percentage of inductor ripple current to increase for low load currents, the inductor value and size can be kept relatively low.

When operating in the continuous mode, the inductor current waveform ranges from a triangular to a sawtooth type of waveform (depending on the input voltage), with the average value of this current waveform equal to the DC output load current.

Inductors are available in different styles such as pot core, toroid, E-core, bobbin core, and so forth, as well as different core materials, such as ferrites and powdered iron. The least expensive, the bobbin, rod or stick core, consists of wire wound on a ferrite bobbin. This type of construction makes for an inexpensive inductor, but because the magnetic flux is not completely contained within the core, it generates more Electro-Magnetic Interference (EMl). This magnetic flux can induce voltages into nearby printed-circuit traces, thus causing problems with both the switching regulator operation and nearby sensitive circuitry, and can give incorrect scope readings because of induced voltages in the scope probe (see Open-Core Inductors).

When multiple switching regulators are located on the same PCB, open-core magnetics can cause interference between two or more of the regulator circuits, especially at high currents. A torroid or E-core inductor (closed magnetic structure) should be used in these situations.

The inductors listed in the selection chart include ferrite E-core construction for Schottky, ferrite bobbin core for Renco and Coilcraft, and powdered iron toroid for Pulse Engineering.

Exceeding the maximum current rating of the inductor can cause the inductor to overheat because of the copper wire losses, or the core may saturate. If the inductor begins to saturate, the inductance decreases rapidly and the inductor begins to look mainly resistive (the DC resistance of the winding). This can cause the switch current to rise very rapidly and force the switch into a cycle-by-cycle current limit, thus reducing the DC output load current. This can also result in overheating of the inductor or the LM2596. Different inductor types have different saturation characteristics, so consider this when selecting an inductor.

The inductor manufacturer's data sheets include current and energy limits to avoid inductor saturation.

For continuous mode operation, see the inductor selection graphs in Figure 27 through Figure 30.

LM2596 01258324.pngFigure 27. LM2596-3.3
LM2596 01258326.pngFigure 29. LM2596-12
LM2596 01258325.pngFigure 28. LM2596-5.0
LM2596 01258327.pngFigure 30. LM2596-ADJ

Table 1. Inductor Manufacturers Part Numbers

L15 22 0.99 67148350 67148460 RL-1284-22-43 RL1500-22 PE-53815 PE-53815-S DO3308-223
L21 68 0.99 67144070 67144450 RL-5471-5 RL1500-68 PE-53821 PE-53821-S DO3316-683
L22 47 1.17 67144080 67144460 RL-5471-6 PE-53822 PE-53822-S DO3316-473
L23 33 1.40 67144090 67144470 RL-5471-7 PE-53823 PE-53823-S DO3316-333
L24 22 1.70 67148370 67148480 RL-1283-22-43 PE-53824 PE-53825-S DO3316-223
L25 15 2.10 67148380 67148490 RL-1283-15-43 PE-53825 PE-53824-S DO3316-153
L26 330 0.80 67144100 67144480 RL-5471-1 PE-53826 PE-53826-S DO5022P-334
L27 220 1.00 67144110 67144490 RL-5471-2 PE-53827 PE-53827-S DO5022P-224
L28 150 1.20 67144120 67144500 RL-5471-3 PE-53828 PE-53828-S DO5022P-154
L29 100 1.47 67144130 67144510 RL-5471-4 PE-53829 PE-53829-S DO5022P-104
L30 68 1.78 67144140 67144520 RL-5471-5 PE-53830 PE-53830-S DO5022P-683
L31 47 2.20 67144150 67144530 RL-5471-6 PE-53831 PE-53831-S DO5022P-473
L32 33 2.50 67144160 67144540 RL-5471-7 PE-53932 PE-53932-S DO5022P-333
L33 22 3.10 67148390 67148500 RL-1283-22-43 PE-53933 PE-53933-S DO5022P-223
L34 15 3.40 67148400 67148790 RL-1283-15-43 PE-53934 PE-53934-S DO5022P-153
L35 220 1.70 67144170 RL-5473-1 PE-53935 PE-53935-S
L36 150 2.10 67144180 RL-5473-4 PE-54036 PE-54036-S
L37 100 2.50 67144190 RL-5472-1 PE-54037 PE-54037-S
L38 68 3.10 67144200 RL-5472-2 PE-54038 PE-54038-S
L39 47 3.50 67144210 RL-5472-3 PE-54039 PE-54039-S
L40 33 3.50 67144220 67148290 RL-5472-4 PE-54040 PE-54040-S
L41 22 3.50 67144230 67148300 RL-5472-5 PE-54041 PE-54041-S
L42 150 2.70 67148410 RL-5473-4 PE-54042 PE-54042-S
L43 100 3.40 67144240 RL-5473-2 PE-54043
L44 68 3.40 67144250 RL-5473-3 PE-54044