AX3702

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

35% of the maximum load current.

Table 2 Inductor select for output voltage setting (VCC=5V)

VOUT

1.2V

1.5V

1.8V

2.5V

3.3V

Inductor

2.2uH

2.2uH

2.2uH

2.2uH

2.2uH

Note: Part type MH or M (www.we-online.com)

For output voltages above 2.0V, when light-load efficiency is important, the minimum

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

an inductor with DC series resistance in the 50mΩ to 150mΩ range. For higher efficiency at

heavy loads (above 200mA), 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.

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 4.7µF ceramic capacitor for most applications is

sufficient.

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. Ceramic capacitors with X5R or X7R dielectrics are recommended due to their

low ESR and high ripple current.

Compensation Capacitor Selection

The compensation capacitors for increasing phase margin provide additional stability.

It is required and more than 22pF, Refer to Demo Board Schematic, The optimum values for

C3 (option) is 330pF.

8/22

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Rev1.4 Sep.30, 2021