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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 19 of 47
NXP Semiconductors
SSL4120T
Resonant power supply control IC with PFC
Switching of the power factor correction circuit is inhibited as soon as the voltage on the
SNSBOOST pin rises above V
ovp(SNSBOOST)
. PFC switching resumes as soon as
V
SNSBOOST
drops below V
ovp(SNSBOOST)
again.
Overvoltage protection will also be triggered in the event of an open circuit at the resistor
connected between SNSBOOST and ground.
7.7.10 PFC short circuit/open-loop protection, SCP/OLP-PFC (pin SNSBOOST)
The power factor correction circuit will not start switching until the voltage on the
SNSBOOST pin rises above V
scp(SNSBOOST)
. This acts as short circuit protection for the
boost voltage (SCP-boost).
The SNSBOOST pin draws a small input current I
prot(SNSBOOST)
. If this pin gets
disconnected, the residual current will pull down V
SNSBOOST
, triggering short circuit
protection (SCP-boost). This combination creates an open-loop protection (OLP-PFC).
7.8 HBC controller
The HBC controller converts the 400 V boost voltage from the PFC into one or more
regulated DC output voltages and drives two external MOSFETS in a half-bridge
configuration connected to a transformer. The transformer, which has a leakage
inductance and a magnetizing inductance, forms the resonant circuit in combination with
the resonant capacitor and the load at the output. The regulation is realized via frequency
control.
7.8.1 HBC high-side and low-side driver (pin GATEHS and GATELS)
Both drivers have identical driving capability. The output of each driver is connected to the
equivalent gate of an external high-voltage power MOSFET.
The low-side driver is referenced to pin PGND and is supplied from SUPREG.
The high-side driver is floating. The reference for the high-side driver is pin HB, connected
to the midpoint of the external half-bridge. The high-side driver is supplied from SUPHS
which is connected to the external bootstrap capacitor C
SUPHS
. The bootstrap capacitor is
charged from SUPREG via external diode D
SUPHS
when the low-side MOSFET is on.
7.8.2 HBC boost undervoltage protection, UVP-boost (pin SNSBOOST)
The voltage on the SNSBOOST pin is sensed continuously to prevent the HBC controller
trying to operate at very low boost input voltages. Once V
SNSBOOST
drops below
V
uvp(SNSBOOST),
HBC switching stops the next time GATELS goes HIGH. HBC switching
resumes as soon as V
SNSBOOST
rises above V
start(SNSBOOST).
7.8.3 HBC switch control
HBC switch control determines when the MOSFETs switch on and off. It uses the output
from several other blocks.
• A divider is used to realize alternate switching of the high- and low-side MOSFETs for
each oscillator cycle. The oscillator frequency is twice the half-bridge frequency.
• The controlled oscillator determines the switch-off point.
• Adaptive non-overlap time sensing determines the switch-on point. This is the
adaptive non-overlap time function.
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 20 of 47
NXP Semiconductors
SSL4120T
Resonant power supply control IC with PFC
• Several protection circuits and the state of the SSHBC/EN input determine whether
the resonant converter is allowed to start switching.
Figure 9
provides an overview of typical switching behavior.
7.8.4 HBC Adaptive Non-Overlap (ANO) time function (pin HB)
7.8.4.1 Inductive mode (normal operation)
The high efficiency characteristic of a resonant converter is the result of Zero-Voltage
Switching (ZVS) of the power MOSFETs, also called soft switching. To facilitate soft
switching, a small non-overlap time is required between the on-times of the high- and
low-side MOSFETs. During this non-overlap time, the primary resonant current
(dis-)charges the capacitance of the half-bridge between ground and the boost voltage.
After this (dis-)charge, the body diode of the MOSFET starts conducting and because the
voltage across the MOSFET is zero, there are no switching losses when the MOSFET is
switched on. This mode of operation is called inductive mode because the switching
frequency is above the resonance frequency and the resonant tank has an inductive
impedance.
The time required for the HB transition depends on the amplitude of the resonant current
at the instant of switching. There is a complex relationship between this amplitude, the
frequency, the boost voltage and the output voltage. Ideally the IC should switch the
MOSFET on as soon as the HB transition has been completed. If it waits any longer, the
HP voltage may swing back, especially at high output loads. The advanced adaptive
non-overlap time function takes care of this timing, so that it’s not necessary to chose a
fixed dead time (which is always a compromise). This saves on external components.
Adaptive non-overlap time sensing measures the HB slope after one MOSFET has been
switched off. Normally, the HB slope starts immediately (the voltage starts rising or falling).
Once the transition at the HB node is complete, the slope ends (the voltage stops
rising/falling). This is detected by the ANO time sensor and the other MOSFET is switched
Fig 9. Switching behavior of the HBC
GATELS
GATEHS
HB
I
Tr(HBC)
CFMIN
t
V
Boost
0
0
014aaa857
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 21 of 47
NXP Semiconductors
SSL4120T
Resonant power supply control IC with PFC
on. In this way the non-overlap time is optimized automatically, minimizing switching
losses, even if the HB transition cannot be fully completed. Figure 10
illustrates the
operation of the adaptive non-overlap time function in Inductive mode.
The non-overlap time depends on the HB slope, but has upper and lower limits.
An integrated minimum non-overlap time, t
no(min)
, prevents cross conduction occurring
under any circumstances.
The maximum non-overlap time is limited to the oscillator charge time. If the HB slope
lasts longer than the oscillator charge time (=
1
⁄
4
of HB switching period) the MOSFET is
forced to switch on. In this case the MOSFET is not soft switching. This limitation ensures
that, at very high switching frequencies, the MOSFET on-time is at least
1
⁄
4
of the HB
switching period.
7.8.4.2 Capacitive mode
The description above holds for normal operation with a switching frequency above the
resonance frequency. When an error condition occurs (e.g. output short, load pulse too
high) the switching frequency can be lower than the resonance frequency. The resonant
tank then has a capacitive impedance. In Capacitive mode, the HB slope does not start
after the MOSFET has switched off. Switching on the other MOSFET is not recommended
in this situation. The absence of soft switching increases dissipation in the MOSFETs. In
Capacitive mode, the body diode in the switched-off MOSFET may start conducting.
Switching on the other MOSFET at this instant can result in the immediate destruction of
the MOSFETs.
The advanced adaptive non-overlap time of the SSL4120T will always wait until the slope
at the half-bridge node starts. It guarantees safe switching of the MOSFETs in all
circumstances. Figure 11
illustrates the operation of the adaptive non-overlap time
function in Capacitive mode.
In Capacitive mode, half the resonance period may elapse before the resonant current
changes back to the correct polarity and starts charging the half-bridge node. The
oscillator is slowed down until the half-bridge slope starts to allow this relatively long
waiting time. See Section 7.8.5
for more details on the oscillator.
Fig 10. Adaptive non-overlap time function (normal inductive operation)
fast HB slope
V
Boost
HB
GATELS
GATEHS
0
slow HB slope incomplete HB slope
t
014aaa858
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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