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SSL4120T/1,518

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P27P28-P30P31-P33P34-P36P37-P39P40-P42P43-P45P46-P47
SSL4120T All information provided in this document is subject to legal disclaimers. © NXP B.V. 2012. All rights reserved.
Objective data sheet Rev. 1 — 21 June 2012 16 of 47
NXP Semiconductors
SSL4120T
Resonant power supply control IC with PFC
to keep the regulation loop bandwidth constant over the full mains input range, yielding a
fast transient response on load steps, while still complying with class-D MHR
requirements.
7.7.3 PFC demagnetization sensing (pin SNSAUXPFC)
The voltage on the SNSAUXPFC pin is used to detect transformer demagnetization.
During the secondary stroke, the transformer is magnetized and current flows in the boost
output. During this time, V
SNSAUXPFC
<V
demag(SNSAUXPFC)
(typ. −100 mV) and the PFC
MOSFET is kept off.
After some time, the transformer becomes demagnetized and current stops flowing in the
boost output. From that moment, V
SNSAUXPFC
>V
demag(SNSAUXPFC)
and valley detection is
started. The MOSFET remains off.
To ensure switching continues under all circumstances, the MOSFET is forced to
switch on if the magnetizing of the transformer (V
SNSAUXPFC
<V
demag(SNSAUXPFC)
) is not
detected within t
to(mag)
(typ. 50 μs) after GATEPFC goes LOW.
It is recommended that a 5 kΩ series resistor be connected to this pin to protect the
internal circuitry, against lightning for example. The resistor should be placed close to the
IC on the printed circuit board to prevent incorrect switching due to external disturbances.
7.7.4 PFC valley sensing (pin SNSAUXPFC)
The PFC MOSFET is switched on for the next stroke to reduce switching losses and EMI
if the voltage at the drain of the MOSFET is at its minimum (valley switching),
see Figure 8
.
Fig 7. Relationship between on-time, SNSMAINS voltage and COMPPFC voltage
SSL4120T All information provided in this document is subject to legal disclaimers. © NXP B.V. 2012. All rights reserved.
Objective data sheet Rev. 1 — 21 June 2012 17 of 47
NXP Semiconductors
SSL4120T
Resonant power supply control IC with PFC
Valleys are detected by the valley sensing block connected to the SNSAUXPFC pin. This
block measures the voltage at the auxiliary winding of the PFC transformer, which is a
reduced and inverted copy of the MOSFET drain voltage. When a valley of the drain
voltage (= top at SNSAUXPFC voltage) is detected, the MOSFET is switched on.
If no top is detected on the SNSAUXPFC pin (= valley at the drain) within t
to(vrec)
(typ. 4 μs) after demagnetization was detected, the MOSFET is forced to switch on.
7.7.5 PFC frequency and off-time limiting
For transformer optimization and to minimize switching losses, the switching frequency is
limited to f
max(PFC)
. If the frequency for quasi-resonant operation is above f
max(PFC)
, the
system will switch to Discontinuous conduction mode. The PFC MOSFET is switched on
when the drain-source voltage is at a minimum (valley switching).
The minimum off-time is limited to t
off(PFC)min
to ensure proper control of the PFC MOSFET
under all circumstances.
7.7.6 PFC soft start and soft stop (pin SNSCURPFC)
The PFC controller features a soft start function which slowly increases the primary peak
current at start-up and a soft stop function which slowly decreases the transformer peak
current, before operations are halted. This is to prevent transformer rattle at start-up or
during Burst mode operation.
Fig 8. Demagnetization and valley detection
demagnetized
V
Rect
/N
V
Rect
V
Boost
(V
Boost
− V
Rect
)/N
V
demag(SNSAUXPFC)
0
0
magnetized
Demagnetization
l
Tr(PFC)
Aux(PFC)
Dr(PFC)
GATEPFC
Valley
(= top for detection)
0
off
on
t
014aaa856
SSL4120T All information provided in this document is subject to legal disclaimers. © NXP B.V. 2012. All rights reserved.
Objective data sheet Rev. 1 — 21 June 2012 18 of 47
NXP Semiconductors
SSL4120T
Resonant power supply control IC with PFC
This is achieved by connecting a resistor R
ss(PFC)
and a capacitor C
ss(PFC)
between
pin SNSCURPFC and the current sense resistor R
cur(PFC)
. At start-up, an internal current
source I
ch(ss)(PFC)
charges the capacitor to V
SNSCURPFC
=I
ch(ss)(PFC)
× R
ss(PFC)
. The
voltage is limited to the maximum PFC soft start clamp voltage, V
clamp(ss)PFC
. The
additional voltage across the charged capacitor results in a reduced peak current. After
start-up, the internal current source is switched-off, capacitor C
ss(PFC)
discharges across
R
ss(PFC)
and the peak current increases.
The start level and the time constant of the rising primary current can be adjusted
externally by changing the values of R
ss(PFC)
and C
ss(PFC)
.
Soft stop is achieved by switching on the internal current source I
ch(ss)(PFC)
.This current
charges C
ss(PFC)
and the increasing capacitor voltage reduces the peak current. The
charge current will flow as long as the voltage on pin SNSCURPFC is below the maximum
PFC soft start voltage (typ. 0.5 V). If V
SNSCURPFC
exceeds the maximum PFC soft start
voltage, the soft start current source will start limiting the charge current. To accurately
determine if the capacitor is charged, the voltage is only measured during the off-time of
the PFC power switch. The operation of the PFC is stopped when V
SNSCURPFC
>
V
stop(ss)(PFC)
.
7.7.7 PFC overcurrent regulation, OCR-PFC (pin SNSCURPFC)
The maximum peak current is limited cycle-by-cycle by sensing the voltage across an
external sense resistor (R
cur(PFC)
) connected to the source of the external MOSFET. The
voltage is measured via the SNSCURPFC pin and is limited to V
ocr(PFC)
.
A voltage peak will appear on V
SNSCURPFC
when the PFC MOSFET is switched on due to
the discharging of the drain capacitance. The leading edge blanking time, t
leb(PFC)
,
ensures that the overcurrent sensing block will not react to this transitory peak.
7.7.8 PFC mains undervoltage protection/brownout protection, UVP-mains
(pin SNSMAINS)
The voltage on the SNSMAINS pin is sensed continuously to prevent the PFC trying to
operate at very low mains input voltages. PFC switching stops as soon as V
SNSMAINS
drops below V
uvp(SNSMAINS)
. Mains undervoltage protection is also called brownout
protection.
V
SNSMAINS
is clamped to a minimum value of V
pu(SNSMAINS)
for fast restart as soon as the
mains input voltage recovers after a mains-dropout. The PFC (re)starts once V
SNSMAINS
exceeds the start level V
start(SNSMAINS)
.
7.7.9 PFC boost overvoltage protection, OVP-boost (pin SNSBOOST)
An overvoltage protection circuit has been built in to prevent boost overvoltages during
load steps and mains transients.
I
Cur PFC()pk()
V
ocr PFC()
I
ch ss()PFC()
R
ss PFC()
×()–
R
cur PFC()
---------------------------------------------------------------------------------------------
=
τ R
ss PFC()
C
ss PFC()
×=
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P27P28-P30P31-P33P34-P36P37-P39P40-P42P43-P45P46-P47

SSL4120T/1,518

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Manufacturer:
NXP Semiconductors
Description:
Display Drivers & Controllers Resonant powersupply controller with PFC
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