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LT1618 Datasheet(PDF) 6 Page - Linear Technology |
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LT1618 Datasheet(HTML) 6 Page - Linear Technology |
6 / 16 page LT1618 6 sn1618 1618fas Capacitor Selection Low ESR (equivalent series resistance) capacitors should be used at the output to minimize the output ripple voltage. Multilayer ceramic capacitors are an excellent choice. They have an extremely low ESR and are available in very small packages. X5R and X7R dielectrics are preferred, 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 high output current designs. Converters with lower output currents may need only a 1µF or 2.2µF output capacitor. Solid tantalum or OSCON capacitors can be used, but they will occupy more board area than a ceramic and will have a higher ESR for APPLICATIONS INFORMATION Inductor Selection Several inductors that work well with the LT1618 are listed in Table 1, although there are many other manufacturers and devices that can be used. Consult each manufacturer for more detailed information and for their entire selection of related parts. Many different sizes and shapes are available. Ferrite core inductors should be used to obtain the best efficiency, as core losses at 1.4MHz are much lower for ferrite cores than for the cheaper powdered-iron ones. Choose an inductor that can handle the necessary peak current without saturating, and ensure that the inductor has a low DCR (copper-wire resistance) to mini- mize I2R power losses. A 4.7µH or 10µH inductor will be a good choice for many LT1618 designs. Table 1. Recommended Inductors L MAX HEIGHT PART (µH) (mΩ) (mm) VENDOR CDRH5D18-4R1 4.1 57 2.0 Sumida CDRH5D18-100 10 124 2.0 (847) 956-0666 CR43-2R2 2.2 71 3.5 www.sumida.com CR43-4R7 4.7 109 3.5 CR43-100 10 182 3.5 CR54-100 10 100 4.8 LQH3C1R0M24 1.0 78 2.0 Murata LQH3C2R2M24 2.2 126 2.0 (814) 237-1431 LQH3C4R7M24 4.7 260 2.0 www.murata.com the same footprint device. Always use a capacitor with a sufficient voltage rating. Ceramic capacitors also make a good choice for the input decoupling capacitor, which should be placed as close as possible to the VIN pin of the LT1618. A 1µF to 4.7µF input capacitor is sufficient for most applications. Table 2 shows a list of several ceramic capacitor manufacturers. Consult the manufacturers for detailed information on their entire selection of ceramic parts. Table 2. Recommended Ceramic Capacitor Manufacturers VENDOR PHONE URL Taiyo Yuden (408) 573-4150 www.t-yuden.com Murata (814) 237-1431 www.murata.com Kemet (408) 986-0424 www.kemet.com Diode Selection Schottky diodes, with their low forward voltage drop and fast switching speed, are the ideal choice for LT1618 applications. Table 3 shows several Schottky diodes that work well with the LT1618. Many different manufacturers make equivalent parts, but make sure that the component chosen has a sufficient current rating and a voltage rating greater than the output voltage. The diode conducts cur- rent only when the power switch is turned off (typically less than half the time), so a 0.5A or 1A diode will be sufficient for most designs. The companies below also offer Schottky diodes with higher voltage and current ratings. Table 3. Recommended Schottky Diodes 1A PART 0.5A PART VENDOR PHONE/URL UPS120 Microsemi (510) 353-0822 UPS130 www.microsemi.com UPS140 MBRM120 MBR0520 ON Semiconductor (800) 282-9855 MBRM130 MBR0530 www.onsemi.com MBRM140 MBR0540 B120 B0520 Diodes, Inc (805) 446-4800 B130 B0530 www.diodes.com B140 B0540 |
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