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

Rev.1.3 Nov.26, 2019

AX3518



APPLICATION INFORMATION

Setting the Output Voltage

Application circuit item shows the basic application circuit with AX3518 adjustable

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

equation:

VOUT = 0.8V × (1+

3

R

2

R

)

Table 1 Resistor select for output voltage setting

VOUT

R3

R2

1.2V

600K

300K

1.5V

380K

330K

1.8V

310K

390K

2.5V

220K

470K

3.3V

150K

470K

Inductor Selection

For most designs, the AX3518 operates with inductors of 2.2µH to 3.3µH. Low

inductance values are physically smaller but require faster switching, which results in some

efficiency loss.

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 3200mA, ΔIL= 480mA.

For output voltages above 3.0V, when light-load efficiency is important, the

recommended inductor is 2.2µH. For optimum voltage-positioning load transients, choose

an inductor with DC series resistance in the 30mΩ to 100mΩ range. For higher efficiency at

heavy loads (above 300mA), or minimal load regulation (but some transient overshoot), the

resistance should be kept below 100mΩ. 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 (3200mA + 240mA).

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. Ceramic

capacitors with X5R or X7R dielectrics are highly recommended because of their low ESR

and small temperature coefficients. A 22µF ceramic capacitor for most applications is

sufficient.