Datasheet

8

002-34772 Rev. *F

2023-06-13

EZ-PD™ PAG2P primary-side startup controller

Functional description

3.2

Soft-start

The soft-start feature allows PAG2P to gradually increase the output voltage of the flyback converter till the

secondary side takes control of the regulation. Soft-start is used during initial start-up sequence and fault

condition. The duration of the soft-start is controlled by an external capacitor connected to the SS pin and the

frequency of soft-start is determined by an external resistor connected to the RT pin. An internal current source

of ISSCURR charges the external capacitor and the maximum amplitude for the soft-start ramp is 3.75 V. A 3.75 V

dictates the maximum duty cycle. Duty cycle is gradually increased from 1% to maximum 70% according to the

soft-start capacitor.

Figure 5

Soft-start operation

A Soft-start time is calculated via following equation. A bigger soft-start capacitance allows a longer soft-start

time. A typical soft-start time is about 41.67 ms when the 0.1 μF soft-start capacitor is used.

VSS(t)

GDL(t)

ISSCURR(t)

4.8 μA

VCS(t)

VCS.TH1

3.75 V

D/Cmin

D/Cmax

t

t

t

t

EZ-PD™

PAG2P

PULSEIN

ISSCURR

DRV_GPIO

CSS

SS

VSS

1.75 V

tSS

CSS

2.0V

ISSCURR

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