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LTC3443 Datasheet(PDF) 11 Page - Linear Technology |
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LTC3443 Datasheet(HTML) 11 Page - Linear Technology |
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11 / 16 page  LTC3443 11 sn3443 3443fs COMPONENT SELECTION APPLICATIO S I FOR ATIO For high efficiency, choose an inductor with a high fre- quency core material, such as ferrite, to reduce core loses. The inductor should have low ESR (equivalent series resistance) to reduce the I2R losses, and must be able to handle the peak inductor current without saturating. Molded chokes or chip inductors usually do not have enough core to support the peak inductor currents in the 1A to 2A region. To minimize radiated noise, use a toroid, pot core or shielded bobbin inductor. See Table 1 for suggested components and Table 2 for a list of component suppliers. Table 1. Inductor Vendor Information SUPPLIER PHONE FAX WEB SITE Coilcraft (847) 639-6400 (847) 639-1469 www.coilcraft.com Coiltronics (561) 241-7876 (561) 241-9339 www.coiltronics.com Murata USA: USA: www.murata.com (814) 237-1431 (814) 238-0490 (800) 831-9172 Sumida USA: www.japanlink.com/ (847) 956-0666 (847) 956-0702 sumida Japan: 81(3) 3607-5111 81(3) 3607-5144 Output Capacitor Selection The bulk value of the capacitor is set to reduce the ripple due to charge into the capacitor each cycle. The steady state ripple due to charge is given by: %_ •– • •• % %_ •– • •• • % () ( ) () () () Ripple Boost IV V CV f Ripple Buck IV V CV V f OUT MAX OUT IN MIN OUT OUT OUT MAX IN MAX OUT OUT IN MAX OUT = () = () 100 100 2 where COUT = output filter capacitor, F The output capacitance is usually many times larger in order to handle the transient response of the converter. For a rule of thumb, the ratio of the operating frequency to the unity-gain bandwidth of the converter is the amount the output capacitance will have to increase from the 12 11 10 9 8 7 1 2 3 4 5 6 FB VC VIN PVIN VOUT MODE SHDN/SS GND PGND SW1 SW2 PGND VIN VOUT GND MULTIPLE VIAS 3443 F06 Figure 6. Recommended Component Placement. Traces Carrying High Current are Direct. Trace Area at FB and VC Pins are Kept Low. Lead Length to Battery Should be Kept Short. VOUT and VIN Ceramic Capacitors Close to the IC Pins Inductor Selection The high frequency operation of the LTC3443 allows the use of small surface mount inductors. The inductor cur- rent ripple is typically set to 20% to 40% of the maximum inductor current. For a given ripple the inductance terms are given as follows: L VV V f I Ripple V H L VV V f I Ripple V H IN MIN OUT IN MIN OUT MAX OUT OUT IN MAX OUT OUT MAX IN MAX > () > () () () () () () () •– • •• % • , •– • •• % • 2 2 100 100 where f = operating frequency, Hz %Ripple = allowable inductor current ripple, % VIN(MIN) = minimum input voltage, V VIN(MAX) = maximum input voltage, V VOUT = output voltage, V IOUT(MAX) = maximum output load current |
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