SSL4120T datasheet(16/47 Pages) NXP

16 / 47 page

SSL4120T

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Objective data sheet

Rev. 1 — 21 June 2012

16 of 47

NXP Semiconductors

SSL4120T

Resonant power supply control IC with PFC

to keep the regulation loop bandwidth constant over the full mains input range, yielding a

fast transient response on load steps, while still complying with class-D MHR

requirements.

7.7.3 PFC demagnetization sensing (pin SNSAUXPFC)

The voltage on the SNSAUXPFC pin is used to detect transformer demagnetization.

During the secondary stroke, the transformer is magnetized and current flows in the boost

output. During this time, VSNSAUXPFC <Vdemag(SNSAUXPFC) (typ.

−100 mV) and the PFC

MOSFET is kept off.

After some time, the transformer becomes demagnetized and current stops flowing in the

boost output. From that moment, VSNSAUXPFC >Vdemag(SNSAUXPFC) and valley detection is

started. The MOSFET remains off.

To ensure switching continues under all circumstances, the MOSFET is forced to

switch on if the magnetizing of the transformer (VSNSAUXPFC <Vdemag(SNSAUXPFC)) is not

detected within tto(mag) (typ. 50

μs) after GATEPFC goes LOW.

It is recommended that a 5 k

Ω series resistor be connected to this pin to protect the

internal circuitry, against lightning for example. The resistor should be placed close to the

IC on the printed circuit board to prevent incorrect switching due to external disturbances.

7.7.4 PFC valley sensing (pin SNSAUXPFC)

The PFC MOSFET is switched on for the next stroke to reduce switching losses and EMI

if the voltage at the drain of the MOSFET is at its minimum (valley switching),

see Figure 8.

Fig 7.

Relationship between on-time, SNSMAINS voltage and COMPPFC voltage

on-time

Vton(COMPPFC)max

Vton(COMPPFC)zero VCOMPPFC

014aaa855

ton(max)(lowmains)

ton(max)(highmains)

VSNSMAINS = 0.9 V

VSNSMAINS = 3.3 V

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