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

Rev.1.5 Oct.16, 2019

AX3121

EN/SS

This pin can be supplied shutdown or soft start function. It is inside pull high function.

For normal application, the pin must be connected a capacitor to ground. There is a 6uA

current to charge this capacitor, vary the different capacitor value to control soft start time.

Allow the switching regulator circuit to be shutdown pulling this pin below a 0.4V threshold

voltage; the shutdown supply current is approximately 45uA.

The soft-start time can be calculated by below formula, please refer the formula to

design.

dT1

dT2

dV1

V

V

EN/SS

OUT

1.25V (D=100%)

0.25V (D=0%)

COMP

V

Internal OSC.

250KHz

Typ.

dV2

EN/SS

V

IEN/SS2 vs. Duty

0

1

2

3

4

5

6

0

10

20

30

40

50

60

70

80

90

100

Duty (%)

Calculate Start-up Delay Time (dT1)



dT1= C6 × dV1 ÷IEN/SS1

Where:

IEN/SS1=6uA

C6=10nF~1000nF

dV1=0.76V (EN/SS VIH)

Calculate Soft Start Time (dT2)

dT2=C6 × dV2 ÷ IEN/SS2

Where:

dV2=(1.25-0.25)×Duty= VOUT/VIN (V)

IEN/SS2＝5.64-(5.64-3.03)×dV2÷(1.25-0.25)

＝

5.64-2.61×VOUT/VIN (uA)

※

Duty (%) = VOUT/VIN × 100