SSL8516T datasheet(16/33 Pages) NXP

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SSL8516T

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Product data sheet

Rev. 1 — 5 May 2014

16 of 33

NXP Semiconductors

SSL8516T

Greenchip PFC and flyback controller

7.3.6 Soft-start (FBSENSE pin)

To prevent audible transformer noise during start-up, the soft-start function slowly

increases the transformer peak current. Place a capacitor CSS2 in parallel with resistor

RSS2 (see Figure 13) to implement the soft-start function.

An internal current source charges the capacitor to:

(5)

with a maximum of 0.55 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.

(6)

The soft-start current Istart(soft)fb switches on when VCC reaches Vstartup. When the

VFBSENSE reaches 0.55 V, the flyback converter starts switching.

The charging current Istart(soft)fb flows when the VFBSENSE is < 0.55 V. If VFBSENSE exceeds

0.55 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 11. Time-out protection circuit

Fig 12. SSL8516T time-out protection (signals) and safe restart

start soft

fb

SS2





start soft

fb

SS2



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