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Rev.1.9 Aug.05, 2010

AX3101

Setting the Output Voltage

Application circuit item shows the basic application circuit with adjustable output

version. The external resistor sets the output voltage according to the following equation:











 





2

1

1

8

.

0

R

R

V

V

OUT

Table 1 Resistor select for output voltage setting

VOUT

R2

R1

5V

1.3K

6.8K

5.6K

30K

3.3V

1.5K

4.7K

5.6K

18K

2.5V

2.2K

4.7K

1.8V

2K

2.5K

1.5V

2.2K

2.0K

1.2V

3K

1.5K

1.0V

3K

0.75K

The R2 setting 5.6k that No load current can be reduce to under 4mA for EL CAP.

Inductor Selection

For most designs, the operates with inductors of 15µH to 33µH. The inductor value

can be derived from the following equation:





f

I

V

V

V

V

L

OSC

L

IN

OUT

IN

OUT













Where is inductor Ripple Current. Large value inductors lower ripple current and

small value inductors result in high ripple currents. Choose inductor ripple current

approximately 15% of the maximum load current 2A, ΔIL=0.3A. The DC current rating of

the inductor should be at least equal to the maximum load current plus half the ripple

current to prevent core saturation (2A+0.15A).

Input Capacitor Selection

This capacitor should be located close to the IC using short leads and the voltage

rating should be approximately 1.5 times the maximum input voltage. The RMS current

rating requirement for the input capacitor of a buck regulator is approximately 1⁄2 the DC

load current. A low ESR input capacitor sized for maximum RMS current must be used. A

220µF low ESR capacitor for most applications is sufficient.