AX3702

Soft Start

AX3702 has built-in soft start of 1ms. During the soft start period, output voltage is

ramped up linearly to the regulation voltage, independent of the load current level and output

capacitor value.

Current Limit and Hiccup Mode

AX3702 has cycle-by-cycle HS current limit protection to prevent inductor current

from running away. Once HS current limit is triggered, AX3702 will turn on LS and wait for the

inductor to drop down to a pre-determined level before the HS can be turned on again. If this

current limit condition is repeated for a sustained long period of time, AX3702 will consider it

over-load or short circuit. Either way, AX3702 will enter hiccup mode, where it stop switching

for a pre-determined period of time before automatically re-try to start up again. It always starts

up with soft-start to limit inrush current and avoid output overshoot.



APPLICATION INFORMATION

Setting the Output Voltage

Application circuit item shows the basic application circuit with AX3702 adjustable

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

equation:

)

2

R

1

R

+

1(

×

V

6.

0

=

V

OUT

Table 1 Resistor select for output voltage setting

VOUT

R2

R1

1.2V

30K

30K

1.5V

30K

45K

1.8V

30K

60K

2.5V

30K

95K

3.3V

30K

135K

Inductor Selection

For most designs, the AX3702 operates with inductors of 1µH to 4.7µH. Low

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

efficiency loss. The inductor value can be derived from the following equation:

(

)

f

I

V

V

V

V

L

OSC

L

IN

OUT

IN

OUT

×

×

−

×

=

∆

7/22

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Rev1.4 Sep.30, 2021