DocID027688 Rev 3

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PM8908

Application information

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6.5

Output capacitors

The output capacitors are basic components to define the ripple voltage across the output

and for the fast transient response of the power supply. They depend on the output voltage

ripple requirements, as well as any output voltage deviation requirement during a load

transient.

During steady-state conditions, the output voltage ripple is influenced by both the ESR and

the capacitive value of the output capacitors as follows:

Equation 6

Equation 7

where

takes into consideration the output capacitor charge and discharge as a consequence of the

inductor current ripple.

6.6

Input capacitors

The input capacitor bank is designed considering, mainly, the input RMS current that

follows:

Equation 8

input capacitor ESR and, in the worst case, are:

Equation 9

V

OUT_ESR

I

L

ESR



=

V

OUT_C

I

L

1

8C

OUT

F

SW



---------------------------------------



=

I

rms

I

OUT

D1

D

–







=

PESR

I





2



=