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

Rev.1.5 Oct.16, 2019

AX3121

Example：

@ C6=100nF, VIN=12V, VOUT=2.5V, IOUT=1A, EN-ON

dT1= C6 × dV1 ÷ IEN/SS1 = 100n x 0.76 ÷ 6u = 12.67mS

dT2=C6 × dV2 ÷ IEN/SS2 = 100n x 0.208 ÷ 5.1u = 4.08mS

Inductor Selection

For most designs, the inductor is suggested 22µH to 33µH. Please refer the below

table to design.

L1 recommend value (VIN=12V ,IOUT=3.5A)

VOUT

1.2V

1.8V

2.5V

3.3V

5V

L1 Value

22uH

22H

22uH

33uH

33uH

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 3.5A, ΔIL=0.52A. 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 (3.5A+0.26A).

Input Capacitor Selection

The input capacitor reduces the surge current drawn from the input and switching

noise from the device. The input capacitor impedance at the switching frequency shall be

less than input source impedance to prevent high frequency switching current passing to

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

The capacitor voltage rating should be at least 1.5 times greater than the input

voltage, and often much higher voltage ratings are needed to satisfy.

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

ESR requirements needed for low output ripple voltage.

The capacitor voltage rating should be at least 1.5 times greater than the input

voltage, and often much higher voltage ratings are needed to satisfy.