SSL4101T

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© NXP B.V. 2011. All rights reserved.

Product data sheet

Rev. 1 — 21 April 2011

16 of 29

NXP Semiconductors

SSL4101T

GreenChip III+ SMPS control IC

7.3.7 Maximum on-time

The flyback controller limits the ‘on-time’ of the external MOSFET to 40

μs (typical). When

the ‘on-time’ is longer than 40

μs, the IC stops switching and enters the safe restart mode.

7.3.8 Overvoltage protection (FBAUX pin)

An output overvoltage protection is implemented in the GreenChip III+ series. This works

for the SSL4101T by sensing the auxiliary voltage via the current flowing into pin FBAUX

during the secondary stroke. The auxiliary winding voltage is a well-defined replica of the

output voltage. Voltage spikes are averaged by an internal filter.

If the output voltage exceeds the OVP trip level, an internal counter starts counting

subsequent OVP events. The counter has been added to prevent incorrect OVP detection

which might occur during ESD or lightning events. If the output voltage exceeds the OVP

trip level a few times and not again in a subsequent cycle, the internal counter counts

down at twice the speed it uses when counting up.

However, when typically eight cycles of subsequent OVP events are detected, the IC

assumes a true OVP and the OVP circuit switches the power MOSFET off. As the

protection is latched, the converter only restarts after the internal latch is reset. In a typical

application the mains should be interrupted to reset the internal latch.

accurate OVP detection possible.

Fig 12. Soft start-up of flyback

014aaa020

SOFT START

CONTROL

OCP

+

10

FBSENSE

0.5 V

Istart(soft)fb ≤ 60 μA

S2

RSS2

CSS2

RSENSE2

V

Oovp

()

Ns

N

aux

----------- I

ovp FBAUX

()

R

FBAUX

×

V

clamp FBAUX

()

+

()

=