SSL4101T datasheet(15/29 Pages) NXP

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SSL4101T

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Product data sheet

Rev. 1 — 21 April 2011

15 of 29

NXP Semiconductors

SSL4101T

GreenChip III+ SMPS control IC

7.3.6 Soft start-up (FBSENSE pin)

To prevent audible transformer noise during start-up, the transformer peak current, IDM is

slowly increased by the soft start function. This can be achieved by inserting a resistor and

a capacitor between pin 10, FBSENSE, and the current sense resistor.

An internal current source charges the capacitor to V = Istart(soft)fb × RSS2, with a maximum

of approximately 0.5 V.

The start level and the time constant of the increasing primary current level can be

adjusted externally by changing the values of RSS2 and CSS2.

The soft start current Istart(soft)fb is switched on as soon as VCC reaches Vstartup. When the

voltage on pin FBSENSE has reached 0.5 V, the flyback converter starts switching.

The charging current Istart(soft)(PFC) flows as long as the voltage on pin FBSENSE is below

approximately 0.5 V. If the voltage on pin FBSENSE exceeds 0.5 V, the soft start current

source starts limiting the current. After the flyback converter has started, the soft start

current source is switched off.

Fig 10. Time-out protection circuit

Fig 11. Time-out protection (signals), safe restart in the SSL4101T

014aaa049

FBCTRL

2.5 V

4.5 V

μA

3 k

3.5 V

time-out

014aaa050

4.5 V

2.5 V

VFBCTRL

output

voltage

intended output

voltage not

reached within

time-out time.

intended output voltage

reached within time-out

time.

restart

τsoftstart

SS2

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