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Axelite Confidential Materials, do not copy or distribute without written consent.

Rev.2.1 Oct.04, 2019

AX3050/A



APPLICATON INFORMATION

Output Voltage Setting

Figure1 Output Voltage Setting

Figure 1 shows the connections for setting the output voltage. Select the proper ratio of

the two feedback resistors RFB1 and RFB2 based on the output voltage. Typically, use

RFB2 ≈ 10kΩ and determine RFB1 from the following equation:

)

1

V

1

V

(

R

=

R

OUT

2

FB

1

FB

－

Inductor Selection

The inductor maintains a continuous current to the output load. This inductor current

has a ripple that is dependent on the inductance value:

Higher inductance reduces the peak-to-peak ripple current. The trade off for high

inductance value is the increase in inductor core size and series resistance, and the

reduction in current handling capability. In general, select an inductance value L based on

ripple current requirement:

RIPPLE

OUTMAX

LX

IN

OUT

IN

OUT

K

I

f

V

)

V

V

(

×

V

=

L

－

where VIN is the input voltage, VOUT is the output voltage, fLX is the switching frequency,

IOUTMAX is the maximum output current, and KRIPPLE is the ripple factor. Typically, choose

KRIPPLE = 30% to correspond to the peak-to-peak ripple current being 30% of the maximum

output current.

With this inductor value, the peak inductor current is IOUT × (1 + KRIPPLE/2). Make sure

that this peak inductor current is less than the controller’s current limit. Finally, select the

inductor core size so that it does not saturate at the peak inductor current.