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TPS65070RSLT Datasheet(PDF) 63 Page - Texas Instruments |
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TPS65070RSLT Datasheet(HTML) 63 Page - Texas Instruments |
63 / 93 page L Vout 1 Vin I = Vout L - D ´ ´ ¦ L Lmax outmax I I = I + 2 D TPS65070, TPS65072, TPS65073 TPS650731, TPS650732 www.ti.com SLVS950B – JULY 2009 – REVISED DECEMBER 2009 APPLICATION INFORMATION STEP-DOWN CONVERTERS OUTPUT FILTER DESIGN (INDUCTOR AND OUTPUT CAPACITOR) Inductor Selection The step-down converters operate typically with 2.2 μH output inductor. Larger or smaller inductor values can be used to optimize the performance of the device for specific operation conditions. The selected inductor has to be rated for its DC resistance and saturation current. The DC resistance of the inductance will influence directly the efficiency of the converter. Therefore an inductor with lowest DC resistance should be selected for highest efficiency. Equation 4 can be used to calculate the maximum inductor current under static load conditions. The saturation current of the inductor should be rated higher than the maximum inductor current as calculated with Equation 4. This is recommended because during heavy load transient the inductor current will rise above the calculated value. (4) (5) With f = Switching Frequency (2.25MHz typical) L = Inductor Value ΔIL= Peak to Peak inductor ripple current ILmax = Maximum Inductor current The highest inductor current will occur at maximum Vin. Open core inductors have a soft saturation characteristic and they can usually handle higher inductor currents versus a comparable shielded inductor. A more conservative approach is to select the inductor current rating just for the maximum switch current of the corresponding converter. It must be considered, that the core material from inductor to inductor differs and will have an impact on the efficiency especially at high switching frequencies. Refer to Table 4 and the typical applications for possible inductors. Table 4. Tested Inductors INDUCTOR TYPE RECOMMENDED INDUCTOR VALUE SUPPLIER MAXIMUM DC CURRENT LPS3010 0.6 A 2.2 μH Coilcraft LPS3015 1.2 A 2.2 μH Coilcraft LPS4018 1.5 A 2.2 μH Coilcraft VLCF4020 1.5 A 2.2 μH TDK Output Capacitor Selection The advanced Fast Response voltage mode control scheme of the two converters allow the use of small ceramic capacitors with a typical value of 10 μF, without having large output voltage under and overshoots during heavy load transients. Ceramic capacitors having low ESR values result in lowest output voltage ripple and are therefore recommended. Please refer to for recommended components. If ceramic output capacitors are used, the capacitor RMS ripple current rating will always meet the application requirements. Just for completeness the RMS ripple current is calculated as: Copyright © 2009, Texas Instruments Incorporated Submit Documentation Feedback 63 Product Folder Link(s): TPS65070 TPS65072 TPS65073 TPS650731, TPS650732 |
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