LP6482S datasheet(8/10 Pages) POWER

8 / 10 page

LP6482S-02

May.-2013

Email: marketing@lowpowersemi.com

www.lowpowersemi.com

Page 8 of 10

Preliminary Datasheet

LP6482S

Input Capacitor

The input current to the step-down converter is

discontinuous, and therefore an input capacitor CIN is

required to supply the AC current to the step-down

converter while maintaining the DC input voltage. A

low ESR capacitor is required to keep the noise

minimum at the IC. Ceramic capacitors are preferred,

but tantalum or low-ESR electrolytic capacitors may

also suffice. The input capacitor value should be

greater than 22μF, and the RMS current rating

should be greater than approximately 1/2 of the DC

load current. For insuring stable operation CIN should

be placed as close to the IC as possible. Alternately

a smaller high quality ceramic 0.1μF capacitor may

be placed closer to the IC and a larger capacitor

placed further away. Using this technique, it is

recommended that the larger capacitor type are

either tantalum or electrolytic. All ceramic capacitors

should be placed close to the LP6482S.

Output Capacitor

The output capacitor is required to maintain the DC

output voltage. Low ESR capacitors are preferred to

keep

the

output

voltage

ripple

low.

The

characteristics of the output capacitor also affect the

stability of the regulator control loop. Ceramic,

tantalum, or low ESR electrolytic capacitors are

recommended. In the case of ceramic capacitors, the

impedance at the switching frequency is dominated

by the capacitance. The output voltage ripple is

estimated to be:

VRIPPLE=1.4×VIN×(fLC/f)2

Where VRIPPLE is the output ripple voltage, VIN is the

input voltage, fLC is the resonant frequency of the LC

filter, f is the switching frequency. In the case of

tantalum or low ESR electrolytic capacitors, the ESR

dominates the impedance at the switching frequency,

and so the output ripple is calculated as:

VRIPPLE≈∆I×RESR

Where VRIPPLE is the output voltage ripple, ΔI is the

inductor ripple current, and RESR is the equivalent

series resistance of the output capacitors.

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