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LT3478IFE-1 Datasheet(PDF) 10 Page - Linear Technology |
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LT3478IFE-1 Datasheet(HTML) 10 Page - Linear Technology |
10 / 24 page LT3478/LT3478-1 10 34781f APPLICATIO S I FOR ATIO Inductor Selection Several inductors that work well with the LT3478/LT3478-1 are listed in Table 1. However, there are many other manu- facturers and inductors that can be used. Consult each manufacturer for more detailed information and their entire range of parts. Ferrite cores should be used to obtain the best efficiency. Choose an inductor that can handle the necessary peak current without saturating. Also ensure that the inductor has a low DCR (copper-wire resistance) to minimize I2R power losses. Values between 4.7µH and 22µH will suffice for most applications. Inductor manufacturers specify the maximum current rating as the current where inductance falls by a given percentage of its nominal value. An inductor can pass a current greater than its rated value without damaging it. Aggressive designs where board space is precious will exceed the maximum current rating of the inductor to save space. Consult each manufacturer to determine how the maximum inductor current is measured and how much more current the inductor can reliably conduct. Capacitor Selection Low ESR (equivalent series resistance) ceramic capaci- tors should be used at the output to minimize the output ripple voltage. Use only X5R or X7R dielectrics, as these materials retain their capacitance over wider voltage and temperature ranges than other dielectrics. A 4.7µF to 10µF output capacitor is sufficient for most high output current designs. Some suggested manufacturers are listed in Table 2. Diode Selection Schottky diodes, with their low forward voltage drop and fast switching speed, are ideal for LT3478/LT3478-1 ap- plications. Table 3 lists several Schottky diodes that work well. The diode’s average current rating must exceed the application’s average output current. The diode’s maximum reverse voltage must exceed the application’s output volt- age. A 4.5A diode is sufficient for most designs. For PWM dimming applications, be aware of the reverse leakage current of the diode. Lower leakage current will drain the output capacitor less, allowing for higher dimming range. The companies below offer Schottky diodes with high voltage and current ratings. Table 1. Suggested Inductors MANUFACTURER PART NUMBER IDC (A) INDUCTANCE (µH) MAX DCR (mΩ)L × W × H (mm) MANUFACTURER CDRH104R-100NC CDRH103RNP-4R7NC-B CDRH124R-100MC CDRH104R-5R2NC 3.8 4 4.5 5.5 10 4.7 10 5.2 35 30 28 22 10.5 × 10.3 × 4.0 10.5 × 10.3 × 3.1 12.3 × 12.3 × 4.5 10.5 × 10.3 × 4.0 Sumida www.sumida.com FDV0630-4R7M 4.2 4.7 49 7.0 × 7.7 × 3.0 Toko www.toko.com UP4B-220 7.6 22 34 22 × 15 × 7.9 Cooper www.cooperet.com Table 2. Ceramic Capacitor Manufacturers MANUFACTURER PHONE NUMBER WEB Taiyo Yuden (408) 573-4150 www.t-yuden.com AVX (803) 448-9411 www.avxcorp.com Murata (714) 852-2001 www.murata.com Table 3. Suggested Diodes MANUFACTURER PART NUMBER MAX CURRENT (A) MAX REVERSE VOLTAGE WEB UPS340 3 40 Microsemi www.microsemi.com B520C B530C B340A B540C PDS560 5 5 3 5 5 30 30 40 40 60 Diodes, Inc. www.diodes.com |
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