Datasheet LTC3400-1 (Analog Devices) - 7

LTC3400-1
U U W U APPLICATIO S I FOR ATIO
The inductor current ripple is typically set for 20% to 40% extremely low ESR and are available in small footprints. A of the maximum inductor current (IP). High frequency 2.2µF to 10µF output capacitor is sufficient for most ferrite core inductor materials reduce frequency depen- applications. Larger values up to 22µF may be used to dent power losses compared to cheaper powdered iron obtain extremely low output voltage ripple and improve types, improving efficiency. The inductor should have low transient response. An additional phase lead capacitor ESR (series resistance of the windings) to reduce the I2R may be required with output capacitors larger than 10µF power losses, and must be able to handle the peak to maintain acceptable phase margin. X5R and X7R inductor current without saturating. Molded chokes and dielectric materials are preferred for their ability to main- some chip inductors usually do not have enough core to tain capacitance over wide voltage and temperature ranges. support the peak inductor currents of 850mA seen on the Low ESR input capacitors reduce input switching noise LTC3400-1. To minimize radiated noise, use a toroid, pot and reduce the peak current drawn from the battery. It core or shielded bobbin inductor. See Table 1 for some follows that ceramic capacitors are also a good choice for suggested components and suppliers. input decoupling and should be located as close as pos-
Table 1. Recommended Inductors
sible to the device. A 4.7µF input capacitor is sufficient for
MAX
virtually any application. Larger values may be used with-
L DCR HEIGHT
out limitations. Table 2 shows a list of several ceramic
PART (
µ
H) m
Ω
(mm) VENDOR
capacitor manufacturers. Consult the manufacturers di- CDRH5D18-4R1 4.1 57 2.0 Sumida rectly for detailed information on their entire selection of CDRH5D18-100 10 124 2.0 (847) 956-0666 ceramic parts. CDRH3D16-4R7 4.7 105 1.8 www.sumida.com CDRH3D16-6R8 170 1.8
Table 2. Capacitor Vendor Information
CR43-4R7 4.7 109 3.5
SUPPLIER PHONE WEBSITE
CR43-100 10 182 3.5 CMD4D06-4R7MC 4.7 216 0.8 AVX (803) 448-9411 www.avxcorp.com CMD4D06-3R3MC 3.3 174 0.8 Murata (714) 852-2001 www.murata.com DS1608-472 4.7 60 2.9 Coilcraft Taiyo Yuden (408) 573-4150 www.t-yuden.com DS1608-103 10 75 2.9 (847) 639-6400 DO1608C-472 4.7 90 2.9 www.coilcraft.com D52LC-4R7M 4.7 84 2.0 Toko
Output Diode
D52LC-100M 10 137 2.0 (408) 432-8282 www.tokoam.com Use a Schottky diode such as an MBR0520L, PMEG2010EA, LQH3C4R7M24 4.7 195 2.2 Murata 1N5817 or equivalent if the converter output voltage is 4.5V www.murata.com or greater. The Schottky diode carries the output current for the time it takes for the synchronous rectifier to turn on. Do not use ordinary rectifier diodes, since the slow recovery
Output and Input Capacitor Selection
times will compromise efficiency. A Schottky diode is also Low ESR (equivalent series resistance) capacitors should strongly recommended for output voltages below 4.5V, be used to minimize the output voltage ripple. Multilayer and will increase converter efficiency by 2% to 3%. ceramic capacitors are an excellent choice as they have 34001f 7