Datasheet LT1618 (Analog Devices) - 6

LT1618
U U W U APPLICATIONS INFORMATION Inductor Selection
the same footprint device. Always use a capacitor with a sufficient voltage rating. Several inductors that work well with the LT1618 are listed in Table 1, although there are many other manufacturers Ceramic capacitors also make a good choice for the input and devices that can be used. Consult each manufacturer decoupling capacitor, which should be placed as close as for more detailed information and for their entire selection possible to the VIN pin of the LT1618. A 1µF to 4.7µF input of related parts. Many different sizes and shapes are capacitor is sufficient for most applications. Table 2 shows available. Ferrite core inductors should be used to obtain a list of several ceramic capacitor manufacturers. Consult the best efficiency, as core losses at 1.4MHz are much the manufacturers for detailed information on their entire lower for ferrite cores than for the cheaper powdered-iron selection of ceramic parts. ones. Choose an inductor that can handle the necessary
Table 2. Recommended Ceramic Capacitor Manufacturers
peak current without saturating, and ensure that the
VENDOR PHONE URL
inductor has a low DCR (copper-wire resistance) to mini- Taiyo Yuden (408) 573-4150 www.t-yuden.com mize I2R power losses. A 4.7µH or 10µH inductor will be Murata (814) 237-1431 www.murata.com a good choice for many LT1618 designs. Kemet (408) 986-0424 www.kemet.com
Table 1. Recommended Inductors L MAX HEIGHT Diode Selection PART (
µ
H) (m
Ω
) (mm) VENDOR
CDRH5D18-4R1 4.1 57 2.0 Sumida Schottky diodes, with their low forward voltage drop and CDRH5D18-100 10 124 2.0 (847) 956-0666 fast switching speed, are the ideal choice for LT1618 CR43-2R2 2.2 71 3.5 www.sumida.com applications. Table 3 shows several Schottky diodes that CR43-4R7 4.7 109 3.5 CR43-100 10 182 3.5 work well with the LT1618. Many different manufacturers CR54-100 10 100 4.8 make equivalent parts, but make sure that the component LQH3C1R0M24 1.0 78 2.0 Murata chosen has a sufficient current rating and a voltage rating LQH3C2R2M24 2.2 126 2.0 (814) 237-1431 greater than the output voltage. The diode conducts cur- LQH3C4R7M24 4.7 260 2.0 www.murata.com rent only when the power switch is turned off (typically less than half the time), so a 0.5A or 1A diode will be
Capacitor Selection
sufficient for most designs. The companies below also offer Schottky diodes with higher voltage and current Low ESR (equivalent series resistance) capacitors should ratings. be used at the output to minimize the output ripple voltage. Multilayer ceramic capacitors are an excellent choice.
Table 3. Recommended Schottky Diodes
They have an extremely low ESR and are available in very
1A PART 0.5A PART VENDOR PHONE/URL
small packages. X5R and X7R dielectrics are preferred, as UPS120 Microsemi (510) 353-0822 these materials retain their capacitance over wider voltage UPS130 www.microsemi.com UPS140 and temperature ranges than other dielectrics. A 4.7µF to 10 MBRM120 MBR0520 ON Semiconductor (800) 282-9855 µF output capacitor is sufficient for high output current MBRM130 MBR0530 www.onsemi.com designs. Converters with lower output currents may need MBRM140 MBR0540 only a 1µF or 2.2µF output capacitor. Solid tantalum or B120 B0520 Diodes, Inc (805) 446-4800 OSCON capacitors can be used, but they will occupy more B130 B0530 www.diodes.com board area than a ceramic and will have a higher ESR for B140 B0540 sn1618 1618fas 6