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LM2852 Datasheet(PDF) 11 Page - Texas Instruments |
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LM2852 Datasheet(HTML) 11 Page - Texas Instruments |
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11 / 25 page  'IL = 500 kHz x 15 PH 1.2V x 5V (5V - 1.2V) = 121.6 mA 'IL = f x L D x (VIN - VOUT) LM2852 www.ti.com SNVS325D – JANUARY 2005 – REVISED APRIL 2013 CHOOSING AN INDUCTANCE VALUE The current ripple present in the output filter inductor is determined by the input voltage, output voltage, switching frequency and inductance according to the following equation: where • ΔIL is the peak-to-peak current ripple. • D is the duty cycle VOUT/VIN. • VIN is the input voltage applied to the PVIN pin. • VOUT is the output voltage of the switcher. • f is the switching frequency. • L is the inductance of the output filter inductor. (3) Knowing the current ripple is important for inductor selection since the peak current through the inductor is the load current plus one half the ripple current. Care must be taken to ensure the peak inductor current does not reach a level high enough to trip the current limit circuitry of the LM2852. As an example, consider a 5V to 1.2V conversion and a 500kHz switching frequency. According to Table 1, a 15µH inductor may be used. Calculating the expected peak-to-peak ripple, (4) The maximum inductor current for a 2A load would therefore be 2A plus 60.8 mA, 2.0608A. As shown in the ripple equation, the current ripple is inversely proportional to inductance. OUTPUT FILTER INDUCTORS Once the inductance value is chosen, the key parameter for selecting the output filter inductor is its saturation current (Isat) specification. Typically Isat is given by the manufacturer as the current at which the inductance of the coil falls to a certain percentage of the nominal inductance. The Isat of an inductor used in an application should be greater than the maximum expected inductor current to avoid saturation. Below is a table of inductors that may be suitable in LM2852 applications. Table 2. LM2852 Output Filter Inductors Inductance (µH) Part Number Vendor 1 DO1608C-102 Coilcraft 1 DO1813P-102HC Coilcraft 6.8 DO3316P-682 Coilcraft 7 MSS1038-702NBC Coilcraft 10 DO3316P-103 Coilcraft 10 MSS1038-103NBC Coilcraft 12 MSS1038-123NBC Coilcraft 15 D03316P-153 Coilcraft 15 MSS1038-153NBC Coilcraft 18 MSS1038-183NBC Coilcraft 22 DO3316P-223 Coilcraft 22 MSS1038-223NBC Coilcraft 22 DO3340P-223 Coilcraft 27 MSS1038-273NBC Coilcraft 33 MSS1038-333NBC Coilcraft 33 DO3340P-333 Coilcraft Copyright © 2005–2013, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Links: LM2852 |
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