SSL4120 datasheet(17/48 Pages) NXP

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SSL4120

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Product data sheet

Rev. 2 — 1 November 2012

17 of 48

NXP Semiconductors

SSL4120

Resonant power supply controller IC with PFC for LED lighting

Figure 7 illustrates the relationship between VSNSMAINS, VCOMPPFC and the on-time. The

compensation makes it is possible to keep the regulation loop bandwidth constant over

the full mains input range. This feature provides a fast transient response on load steps,

while still meeting the Class-C MHR requirements.

7.7.3 PFC demagnetization sensing (SNSAUXPFC pin)

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) = 100 mV and the PFC

MOSFET remains switched off.

When the transformer becomes demagnetized, the current stops flowing to the boost

output VSNSAUXPFC >Vdemag(SNSAUXPFC) and valley detection is started. The MOSFET

remains switched off.

To ensure that 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) =50 s after the GATEPFC pin goes LOW.

Connect a 5 k

 series resistor to this pin to protect the internal circuitry, against lightning

for example. Place the resistor close to the IC on the PCB to prevent incorrect switching

due to external disturbances.

7.7.4 PFC valley sensing (SNSAUXPFC pin)

If the voltage at the MOSFET drain is at its minimum (valley switching), the PFC MOSFET

is switched on for the next stroke. This action reduces switching losses and EMI

(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 = 0.97 V

VSNSMAINS = 3.3 V

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