Setting the Output Voltage

The external resistor divider is used to set the output voltage (see Typical Application on page 1). The

feedback resistor R1 also sets the feedback loop bandwidth with the internal compensation capacitor.

Choose R1 to be around 100kΩ for optimal transient response. R2 is then given by:

1

/

1

2

−

=

FB

out

V

V

R

R

Selecting the Inductor

A 4.7μH to 22μH inductor with a DC current rating of at least 25% percent higher than the maximum

load current is recommended for most applications. For highest efficiency, the inductor DC resistance

should be less than 15mΩ. For most designs, the inductance value can be derived from the following

equation.

OSC

L

in

out

in

out

f

I

V

V

V

V

L

×

△

×

−

×

=

)

(

Where ΔIL is the inductor ripple current. Choose inductor ripple current to be approximately 30% if the

maximum load current, 2A. The maximum inductor peak current is:

2

)

(

L

LOAD

MAX

L

I

I

I

△

+

=

Under light load conditions below 100mA, larger inductance is recommended for improved efficiency.

Selecting the Output Capacitor

The output capacitor (C2) is required to maintain the DC output voltage. Ceramic, tantalum, or low

ESR electrolytic capacitors are recommended. Low ESR capacitors are preferred to keep the output

voltage ripple low. The output voltage ripple can be mated by:

]

[

×

×

+

×

]

×

×

=

△

2

8

1

1

C

f

R

V

V

L

f

V

V

S

ESR

IN

OUT

S

OUT

OUT

Function Description(Cont.)

2018. 12. 27

5/8

Revision No : 0

FC3470