Product Folder Sample 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 18 LM2596 SNVS124D NOVEMBER 1999 REVISED MAY Product Folder Links LM2596 Submit Documentation FeedbackCopyright 1999 2016 Texas Instruments Incorporated Application Information continued 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 Figure 26 IIND Peak to Peak Inductor Ripple Current as a Percentage of the Load Current vs 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 an inductor s maximum current rating may 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 19 LM2596 SNVS124D NOVEMBER 1999 REVISED MAY 2016 Product Folder Links LM2596 Submit Documentation FeedbackCopyright 1999 2016 Texas Instruments Incorporated Application Information continued Figure 27 LM2596 3 3 Figure 28 LM2596 5 0 Figure 29 LM2596 12 Figure 30 LM2596 ADJ Table 1 Inductor Manufacturers Part Numbers INDUCTANCE H CURRENT A SCHOTTKYRENCOPULSE ENGINEERINGCOILCRAFT THROUGH HOLE SURFACE MOUNT THROUGH HOLE SURFACE MOUNT THROUGH HOLE SURFACE MOUNT SURFACE MOUNT L15 220 996714835067148460 RL 1284 22 43 RL1500 22PE 53815PE 53815 SDO3308 223 L21680 996714407067144450RL 5471 5RL1500 68PE 53821PE 53821 SDO3316 683 L22471 176714408067144460RL 5471 6 PE 53822PE 53822 SDO3316 473 L23331 406714409067144470RL 5471 7 PE 53823PE 53823 SDO3316 333 L24 221 706714837067148480 RL 1283 22 43 PE 53824PE 53825 SDO3316 223 L25 152 106714838067148490 RL 1283 15 43 PE 53825PE 53824 SDO3316 153 L263