DIU6931

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DIU6931• V1.1

Input capacitor CIN

This ripple current through input capacitor is calculated as:

ICIN_RMS = IOUT

D)

D(1



(2)

This formula has a maximum at VIN = 2VOUT condition, where ICIN_RMS = IOUT / 2. This simple worst-case

condition is commonly used for DC/DC design.

To minimize the potential noise problem, place a typical X5R or better grade ceramic capacitor really close to

the IN and GND pins. Care should be taken to minimize the loop area formed by CIN, and IN/GND pins. In this

case, a 10 μF low ESR ceramic capacitor is recommended.

Output capacitor COUT

The output capacitor is selected to handle the output ripple noise requirements. Both steady state ripple and

transient requirements must be taken into consideration when selecting this capacitor. For the best performance,

it is recommended to use X5R or better grade ceramic capacitor greater than 22 µF capacitance.

Output inductor L

There are several considerations in choosing this inductor.

1) Choose the inductance to provide the desired ripple current. It is suggested to choose the ripple current

to be about 40% of the maximum output current. The inductance is calculated as:

L =

40%

I

f

)

/V

V

(1

V

MAX

OUT,

SW

MAX

IN,

OUT

OUT







(3)

where fSW is the switching frequency and IOUT,MAX is the maximum load current. The DIU6931 regulator IC is

quite tolerant of different ripple current amplitude. Consequently, the final choice of inductance can be

slightly off the calculation value without significantly impacting the performance.

2) The saturation current rating of the inductor must be selected to be greater than the peak inductor current

under full load conditions.