SSL8516T datasheet(11/33 Pages) NXP

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SSL8516T

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Product data sheet

Rev. 1 — 5 May 2014

11 of 33

NXP Semiconductors

SSL8516T

Greenchip PFC and flyback controller

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.

Connect a capacitor to the PFCTIMER pin (see Section 7.2.7) to prevent the PFC from

switching off due to a dynamic load that leads to repetitive crossing of fsw(fb)swoff(PFC) and

fsw(fb)swon(PFC). 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.

7.2.9 Mains undervoltage lockout/brownout protection (VINSENSE pin)

To prevent the PFC from operating at very low mains input voltages, VVINSENSE is sensed

continuously. When VVINSENSE drops below the Vstop(VINSENSE) level, switching of the PFC

is stopped.

7.2.10 Overvoltage protection (VOSENSE pin)

To prevent output overvoltage during load steps and mains transients, an overvoltage

protection circuit is built in.

Fig 6.

PFC switch on and switch off using the PFCTIMER pin

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