SSL8516T datasheet(10/33 Pages) NXP

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SSL8516T

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Product data sheet

Rev. 1 — 5 May 2014

10 of 33

NXP Semiconductors

SSL8516T

Greenchip PFC and flyback controller

The voltage is limited to Vstart(soft)PFC.

The start level and time constant of the increasing primary current level is externally

adjusted by changing the RSS1 and CSS1 values.

(2)

The charging current Istart(soft)PFC flows while the PFCSENSE pin voltage is < 0.5 V. If

VPFCSENSE exceeds 0.5 V, the soft-start current source starts limiting current Istart(soft)PFC.

When the PFC starts switching, the Istart(soft)PFC current source is switched off; see

Figure 5.

7.2.6 PFC switch-on/switch-off control

When the flyback converter output power (see Section 7.3) is low, the flyback converter

switches to FR mode. When the switching frequency of the flyback in

FR mode < fsw(fb)swoff(PFC) (53 kHz), the PFC circuit is switched off to maintain high

efficiency. Connect a capacitor to the PFCTIMER pin (see Section 7.2.7) to delay the PFC

switching off.

During low-power mode operation and start-up (when PFC is disabled, e.g. at no-load),

the PFCCOMP pin is clamped to a minimum voltage of 3.32 V or 1.18 V and a maximum

voltage of 3.75 V. The minimum clamp voltage depends on VVINSENSE. This voltage limits

the maximum power that is delivered when the PFC switches on again. The upper clamp

voltage ensures that the PFC returns from low-power mode to its normal regulation point

in a limited time.

In FR mode, when the flyback converter switching frequency exceeds

fsw(fb)swon(PFC) (73 kHz), the PFC circuit is switched on. If the flyback converter duty cycle

is > 50 % or VFBCTRL is > 3.75 V, the PFC circuit is also switched on.

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.

Fig 5.

Soft start of the PFC



start soft

PFC

SS1



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