Datasheet LT3478, LT3478-1 (Analog Devices) - 10

LT3478/LT3478-1
U U W U APPLICATIO S I FOR ATIO Inductor Selection Capacitor Selection
Several inductors that work well with the LT3478/LT3478-1 Low ESR (equivalent series resistance) ceramic capaci- are listed in Table 1. However, there are many other manu- tors should be used at the output to minimize the output facturers and inductors that can be used. Consult each ripple voltage. Use only X5R or X7R dielectrics, as these manufacturer for more detailed information and their entire materials retain their capacitance over wider voltage and range of parts. Ferrite cores should be used to obtain the temperature ranges than other dielectrics. A 4.7µF to best effi ciency. Choose an inductor that can handle the 10µF output capacitor is suffi cient for most high output necessary peak current without saturating. Also ensure current designs. Some suggested manufacturers are that the inductor has a low DCR (copper-wire resistance) listed in Table 2. to minimize I2R power losses. Values between 4.7µH and 22µH will suffi ce for most applications.
Diode Selection
Inductor manufacturers specify the maximum current Schottky diodes, with their low forward voltage drop and rating as the current where inductance falls by a given fast switching speed, are ideal for LT3478/LT3478-1 ap- percentage of its nominal value. An inductor can pass a plications. Table 3 lists several Schottky diodes that work current greater than its rated value without damaging it. well. The diode’s average current rating must exceed the Aggressive designs where board space is precious will application’s average output current. The diode’s maximum exceed the maximum current rating of the inductor to save reverse voltage must exceed the application’s output volt- space. Consult each manufacturer to determine how the age. A 4.5A diode is suffi cient for most designs. For PWM maximum inductor current is measured and how much dimming applications, be aware of the reverse leakage more current the inductor can reliably conduct. 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 (m
Ω
) L
×
W
×
H (mm) MANUFACTURER
CDRH104R-100NC 3.8 10 35 10.5 × 10.3 × 4.0 Sumida CDRH103RNP-4R7NC-B 4 4.7 30 10.5 × 10.3 × 3.1 www.sumida.com CDRH124R-100MC 4.5 10 28 12.3 × 12.3 × 4.5 CDRH104R-5R2NC 5.5 5.2 22 10.5 × 10.3 × 4.0 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 5 30 Diodes, Inc. B530C 5 30 www.diodes.com B340A 3 40 B540C 5 40 PDS560 5 60 34781f 10