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LTC3442 Datasheet(PDF) 13 Page - Linear Integrated Systems |
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LTC3442 Datasheet(HTML) 13 Page - Linear Integrated Systems |
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13 / 20 page ![]() LTC3442 13 3442f APPLICATIO S I FOR ATIO COMPONENT SELECTION Table 1. Inductor Vendor Information SUPPLIER PHONE FAX WEB SITE Coilcraft (847) 639-6400 (847) 639-1469 www.coilcraft.com CoEv Magnetics (800) 227-7040 (650) 361-2508 www.circuitprotection.com/magnetics.asp Murata (814) 237-1431 (814) 238-0490 www.murata.com (800) 831-9172 Sumida USA: (847) 956-0666 USA: (847) 956-0702 www.sumida.com Japan: 81(3) 3607-5111 Japan: 81(3) 3607-5144 TDK (847) 803-6100 (847) 803-6296 www.component.tdk.com TOKO (847) 297-0070 (847) 699-7864 www.tokoam.com Figure 6. Recommended Component Placement. Traces Carrying High Current Should be Short and Wide. 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 LTC3442 allows the use of small surface mount inductors. The inductor ripple current 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 fI V H L VV V fI V H BOOST IN MIN OUT IN MIN L OUT BUCK OUT IN MAX OUT L IN MAX > ∆ > ∆ () () () () •( – ) •• •( – ) •• 2 2 12 11 10 9 8 7 1 2 3 4 5 6 FB VC RLIM VIN VOUT BURST SHDN/SS RT SGND SW1 PGND SW2 VIN VOUT GND RT MULTIPLE VIAS 3442 F06 VIN where f = operating frequency, Hz ∆IL = maximum allowable inductor ripple current, A VIN(MIN) = minimum input voltage, V VIN(MAX) = maximum input voltage, V VOUT = output voltage, V IOUT(MAX) = maximum output load current For high efficiency, choose a ferrite inductor with a high frequency core material 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 shielded inductor. See Table 1 for a suggested list of inductor suppliers. Output Capacitor Selection The bulk value of the output filter 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 OUT MAX OUT IN MIN OUT OUT () ( ) •( – ) • •• % 100 2 % RIPPLE_BUCK = IV V CV V f OUT MAX IN MAX OUT OUT IN MAX OUT () () () •( – ) • •• • % 100 where COUT = output filter capacitor in Farads and f = switching frequency in Hz. |
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