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The inductor current ripple is typically set for 20% to 40% of the maximum inductor current (IP). The inductor

should have low ESR (series resistance of the windings) to reduce the power losses, and must be able to handle the

peak inductor current without saturating. To minimize radiated noise, use a shielded bobbin inductor.

Output and Input Capacitor Selection

Low ESR (equivalent series resistance) capacitors should be used to minimize the output voltage ripple.

Multilayer ceramic capacitors are an excellent choice as they have extremely low ESR and are available in small

footprints. A 10

μF to 22μF output capacitor is sufficient for most applications. Larger values may be used to obtain

extremely low output voltage ripple and improve transient response.

Low ESR input capacitors reduce input switching noise and reduce the peak current drawn from the battery. It

follows that ceramic capacitors are also a good choice for input decoupling, and should be located as close as

possible to the device. A 4.7

μF input capacitor is sufficient for virtually any application.

Operating at light loads, a additional feed forward capacitor may be required (for example C1 in the Figure 1)to

maintain acceptable output voltage ripple.

For all the three capacitors above, X5R and X7R dielectric materials are preferred, for their ability to maintain

capacitance over wide voltage and temperature ranges.

HANGZHOU SILAN MICROELECTRONICS CO.,LTD

REV:1.2

2008.07.04

Http://www.silan.com.cn

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