AN11486_15 Datasheet, PDF (10/53 Pages) NXP Semiconductors – GreenChip SSL8516T PFC and flyback controller

NXP Semiconductors
AN11486
GreenChip SSL8516T PFC and flyback controller
5. System description and calculation
5.1 PFC and flyback start conditions
Figure 4 shows the enable conditions of the PFC and the flyback during initial start-up. If
start-up problems occur, check these conditions with an oscilloscope to find the cause of
the problem. The conditions rely on dynamic signals (see Figure 5).
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Fig 4. Controller enable conditions at initial start-up
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5.2 Initial start-up sequence
At initial power-on, the IC has the following start-up sequence (see Figure 5):
1. The HV current source I_HV is set to 1.1 mA and the V_CC pin capacitance is charged to
0.60 V to allow short-circuit detection at the V_CC pin.
2. At V_CC = 0.60 V, I_HV set to 5 mA and the V_CC pin capacitance is quickly charged to
V_startup.
3. At V_startup, I_HV is pinched off. The 30.5 A LATCH pin current source I_O(LATCH) is
switched on to charge the LATCH pin capacitance. The PFCSENSE and FBSENSE
soft-start current sources are switched on.
4. When the LATCH pin capacitance is charged to 582 mV, the PFC can start switching
when V_VOSENSE > 0.5 V and V_VINSENSE > 1.16 V.
5. Two additional conditions that must be met to enable the PFC driver are:
– The PFCSENSE pin soft-start capacitor is charged to 0.5 V
– The PFCCOMP pin capacitance is charged to either 1.19 V or 3.32 V, depending
on V_VINSENSE (V_th(sel)clmp) and I_PFCCOMP > 55 A
6. Conditions to enable the flyback driver are:
– The PFCSENSE pin soft-start capacitor is charged to 0.5 V
– The PFCCOMP pin capacitance is charged to either 1.19 V or 3.32 V, depending
on V_VINSENSE (V_th(sel)clmp) and I_PFCCOMP > 55 A
7. When flyback increases its output voltage, the auxiliary winding takes over the V_CC
supply.
8. If the flyback feedback loop signal is open (due to a fault), the time-out protection on
pin FBCTRL is triggered. Both converters are switched off, V_CC drops to V_th(UVLO), and
the IC performs a safe restart. During safe restart I_HV is set to 1 mA to charge the V_CC
pin capacitance.
AN11486
Application note
All information provided in this document is subject to legal disclaimers.
Rev. 1 — 17 July 2014
© NXP Semiconductors N.V. 2014. All rights reserved.
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