Datasheet LT3477 (Analog Devices) - 9

LT3477
applicaTions inForMaTion Capacitor Selection
percentage of its nominal value—typical y 65%. An Low ESR (equivalent series resistance) ceramic capaci- inductor can pass a current larger than its rated value tors should be used at the output to minimize the output without damaging it. Aggressive designs where board ripple voltage. Use only X5R or X7R dielectrics, as these space is precious will exceed the maximum current rat- materials retain their capacitance over wider voltage and ing of the inductor to save board space. Consult each temperature ranges better than other dielectrics. A 4.7µF manufacturer to determine how the maximum inductor to 10µF output capacitor is sufficient for most high output current is measured and how much more current the current designs. Converters with lower output currents inductor can reliably conduct. may need only a 1µF or 2.2µF output capacitor.
Diode Selection Table 1. Ceramic Capacitor Manufacturers
Schottky diodes, with their low forward voltage drop and
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fast switching speed, are ideal for LT3477 applications. Taiyo Yuden (408) 573-4150 www.t-yuden.com Table 3 lists several Schottky diodes that work well with the AVX (803) 448-9411 www.avxcorp.com LT3477. The diode’s average current rating must exceed Murata (714) 852-2001 www.murata.com the average output current. The diode’s maximum reverse TDK (847) 803-6100 www.component.tdk.com voltage must exceed the output voltage. The diode conducts current only when the power switch is turned off (typically
Inductor Selection
less than 50% duty cycle), so a 3A diode is sufficient for Several inductors that work well with the LT3477 are listed most designs. The companies below also offer Schottky in Table 2. However, there are many other manufacturers diodes with higher voltage and current ratings. and devices that can be used. Consult each manufacturer
Table 3. Suggested Diodes
for more detailed information and their entire range of parts. Ferrite core inductors should be used to obtain the
MANUFACTURER MAX MAX REVERSE PART NUMBER CURRENT (A) VOLTAGE (V) MANUFACTURER
best efficiency. Choose an inductor that can handle the UPS340 n 3 n 40 Microsemi necessary peak current without saturating, and ensure UPS315 3 15 www.microsemi.com that the inductor has a low DCR (copper-wire resistance) B220 n 2 n 20 Diodes, Inc to minimize I2R power losses. A 4.7µH or 10µH inductor B230 2 30 www.diodes.com will suffice for most LT3477 applications. B240 2 40 B320 3 20 Inductor manufacturers specify the maximum current B330 3 30 B340 3 40 rating as the current where the inductance falls to some SBM340 3 40
Table 2. Suggested Inductors MANUFACTURER IDC INDUCTANCE MAX DCR L
×
W
×
H PART NUMBER (A) (µH) (mΩ) (mm) MANUFACTURER
CDRH6D283R0 3 3 24 6.7 × 6.7 × 3.0 Sumida CDRH6D28100 1.7 10 65 6.7 × 6.7 × 3.0 www.sumida.com CDRH4D284R7 1.32 4.7 72 5.0 × 5.0 × 3.0 LM N 05D B4R7M 2.2 4.7 49 5.9 × 6.1 × 2.8 Taiyo Yuden LM N 05D B100K 1.6 10 10 5.9 × 6.1 × 2.8 www.t-yuden.com LQH55DN4R7M01L 2.7 4.7 57 5.7 × 5.0 × 4.7 Murata LQH55DN100M01K 1.7 10 130 5.7 × 5.0 × 4.7 www.murata.com FDV0630-4R7M 4.2 4.7 49 7.0 × 7.7 × 3.0 Toko www.toko.com 3477fd For more information www.linear.com/LT3477 9 Document Outline Description Typical Application Absolute Maximum Ratings Electrical Characteristics Typical Performance Characteristics Pin Functions Package Description Typical Application Related Parts