SSL8516BT datasheet(11/35 Pages) PHILIPS

11 / 35 page

SSL8516BT

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Product data sheet

Rev. 1 — 26 May 2015

11 of 35

NXP Semiconductors

SSL8516BT

Greenchip PFC and flyback controller

7.2.7 PFC switch off delay (PFCTIMER pin)

When the flyback converter switching frequency in FR mode is < fsw(fb)swoff(PFC) (53 kHz),

the IC then outputs a 4.7

A current to the PFCTIMER pin. When V

PFCTIMER reaches 3 V,

the PFC is switched off by performing a soft-stop.

A switch discharges the PFCTIMER pin capacitor when the flyback controller operating

frequency is > fsw(fb)swon(PFC) (73 kHz). At the same moment, the PFC stage is also

switched on.

To prevent that the PFC from switches off because of a dynamic load that leads to

repetitive crossing of fsw(fb)swoff(PFC) and fsw(fb)swon(PFC), connect a capacitor to the

PFCTIMER pin (see Section 7.2.7). A 1 nF minimum capacitor value is recommended to

prevent noise influencing the PFC switch on/ switch off behavior.

The PFCTIMER pin capacitor is also discharged when PFC is on and the flyback

switching frequency is higher than 53 kHz. This feature prevents PFC on/off toggling

during dynamic loads causing the flyback to operate repetitively near fsw(fb)swoff(PFC) and

fsw(fb)swon(PFC).

It is also possible to control PFC switch-on and switch off externally. When VPFCTIMER is

driven below 1.03 V, the PFC stage is on. When the PFCTIMER pin voltage is driven

above 4.4 V, the PFC stage is switched off. The external control overrides the PFC stage

control by the flyback controller (see Figure 6).

The PFCTIMER pin has an internal clamp circuit starting around 10 V with a current

capability of 0.1 mA

7.2.8 Overcurrent protection (PFCSENSE pin)

The maximum peak current is limited cycle-by-cycle by sensing the voltage across an

external sense resistor, RSENSE1, on the source of the external MOSFET. The voltage is

measured using the PFCSENSE pin.

Fig 6.

PFC switch on and switch off using the PFCTIMER pin

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