SSL8516BT Datasheet, PDF (10/35 Pages) NXP Semiconductors – Greenchip PFC and flyback controller

NXP Semiconductors
SSL8516BT
Greenchip PFC and flyback controller
7.2.5 Soft-start (PFCSENSE pin)
To prevent audible transformer noise at start-up or during hiccup, the soft-start function
slowly increases the transformer peak current. To implement a soft-start function, place a
capacitor C_SS1 in parallel with resistor R_SS1 (see Figure 5). An internal current source
charges the capacitor to:
V_PFCSENSE = I_{startsoftPFC}  R_SS1
(1)
The voltage is limited to V_{start(soft)PFC}.
The start level and time constant of the increasing primary current level is externally
adjusted by changing the R_SS1 and C_SS1 values.
_{startsoftPFC} = 3  R_SS1  C_SS1
(2)
The charging current I_{start(soft)PFC} flows while the PFCSENSE pin voltage is < 0.5 V. If
V_PFCSENSE exceeds 0.5 V, the soft-start current source starts limiting current I_{start(soft)PFC}.
When the PFC starts switching, the I_{start(soft)PFC} current source is switched off; see
Figure 5.
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Fig 5. Soft start of the PFC
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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 < f_{sw(fb)swoff(PFC)} (53 kHz), the PFC circuit is switched off to maintain high
efficiency. To delay the PFC switching off, connect a capacitor to the PFCTIMER pin (see
Section 7.2.7).
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 V_VINSENSE. 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
f_{sw(fb)swon(PFC)} (73 kHz), the PFC circuit is switched on. If the flyback converter duty cycle
is > 50 % or V_FBCTRL is > 3.75 V, the PFC circuit is also switched on.
SSL8516BT
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 1 — 26 May 2015
© NXP Semiconductors N.V. 2015. All rights reserved.
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