AN937

Typical application

Doc ID 5655 Rev 15

19/29

Figure 23.

Input capacitance rms current vs. duty cycle

3.3

Output voltage selection

An external voltage divider is required to set the regulated output voltage: I

3.4

Inductor selection

The criteria used in fixing the inductor value has been dictated by the wanted output ripple

voltage, 51mV max., performance obtained of course in combination with output capacitors

too.

The inductor ripple current, fixed at 30% of Iomax, i.e., 0.45 A, requires an inductor value of:

Equation 1

It is possible to plot as a function of Vo and Vccmax at 150 kHz and 200 kHz (see Figure 24

and Figure 25)

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

D

0

0.25

0.5

0.75

D97IN801

V

o

V

REF

1

R2

R3

--------

+

⎝⎠

⎛⎞

⋅

=

L

O

V

O

1D

min

–

()

ΔI

L

f

sw

⋅

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

⋅

=