Fremont Micro Devices

FT441

www.fremontmicro.com

Page 9 of 10

DS441-A2

APPLICATION INFORMATION

Figure4 below shows the typical application circuit with FT441 fixed output versions.

VIN

Vout 1.8V

EN

SW

GND

4

2

1

3

5

2.7~4.2V

10uF

2.2uH

10uF

C1

C2

L1

FT441

Figure 4 Typical Application Circuit with fixed output versions

Inductor Selection

Under normal operation, the inductor maintains continuous current to the output. Its value is chosen based on the

desired ripple current. Large value inductors lower ripple current, and small value inductors result in higher

ripple currents. The inductor value can be derived from the following equation:

osc

L

IN

out

IN

out

f

I

V

V

V

V

L













)

(

Input Capacitor Selection

The input capacitor reduces input voltage ripple to the converter; a 10uF ceramic capacitor is recommended for

most applications.

Output Capacitor Selection

The output capacitor is required to keep the output voltage ripple small and to ensure regulation loop stability.

The output capacitor must have low impedance at the switching frequency. The output ripple ⊿Vout

approximately:

)

8

1

(

OUT

L

OUT

fC

ESR

I

V











Output Voltage Programming

Figure1 above shows the typical application with FT4412 adjustable version. The external resistor sets the output

voltage according to following equation:

)

1

2

1

(

6

.

0

R

R

V

V

OUT





