DIU6921

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DIU6921 • Rev. 1.1

Input capacitor CIN

This ripple current through the input capacitor is calculated as:

D)

D(1

I

I

OUT

CIN_RMS







(2)

To minimize the potential noise problem, place a typical X5R or better-grade ceramic capacitor 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 equivalent series resistance (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 an X5R or better grade ceramic capacitor greater than 22 µF

capacitance.

Output inductor L1

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 DIU6921 regulator IC is quite tolerant of different ripple current amplitudes. 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.

ISAT,MIN>IOUT,MAX +

L

f

2

)

/V

V

(1

V

SW

MAX

IN,

OUT

OUT







(4)