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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 25 of 47
NXP Semiconductors
SSL4120T
Resonant power supply control IC with PFC
Below the level for minimum frequency, V
SNSFB
is clamped at V
clamp(SNSFB)
(typ. 3.2 V).
This clamp enables a fast recovery of the output voltage regulation loop after an
overshoot of the output voltage. The maximum current the clamp can deliver is
I
clamp(SNSFB)
(typ. 7.3 mA).
7.8.7 HBC open-loop protection, OLP-HBC (pin SNSFB)
Under normal operating conditions, the opto-coupler current will be between I
fmin(SNSFB)
and I
fmax(SNSFB)
and will pull down the voltage at pin SNSFB. Due to an error in the
feedback loop, the current could be less than I
fmin(SNSFB)
with the HBC controller
delivering maximum output power.
The HBC controller features open-loop protection (OLP-HBC), which monitors the voltage
on pin SNSFB. When V
SNSFB
exceeds V
olp(SNSFB)
, the protection timer is started. The
Restart state is activated if the OLP condition is still present after the protection time has
elapsed.
7.8.8 HBC soft start (pin SSHBC/EN)
The relationship between switching frequency and output current is not constant. It
depends strongly on the output voltage and the boost voltage. This relationship can be
complex. The SSL4120T contains a soft start function to ensure that the resonant
converter starts or restarts with safe currents. This soft start function forces a start at such
a high frequency that currents will be acceptable under all conditions. Soft start then
slowly decreases the frequency. Normally, output voltage regulation will have taken over
frequency control before soft start has reached its minimum frequency. Limiting the output
current during start-up also limits the rate at which the output voltage rises and prevents
an overshoot.
Soft start utilizes the voltage on pin SSHBC/EN. The timing of the soft start is set by
external capacitor C
ss(HBC)
. Pin SSHBC/EN is also used as an enable input. Soft start
voltage levels are above the enable voltage thresholds.
7.8.8.1 Soft start voltage levels
The relationship between the soft start voltage at pin SSHBC/EN and the voltage at pin
RFMAX, which is directly related to the frequency, is illustrated in Figure 15
.
Fig 14. Transfer function of feedback input
V
SNSFB
0
I
SNSFB
V
pu(SNSFB)
I
fmin(SNSFB)
V
RFMAX
V
RFMAX
0
I
fmax(SNSFB)
0
V
SSHBC
= 8.4 V
I
olp(SNSFB)
V
olp(SNSFB)
V
fmin(SNSFB)
V
fmax(SNSFB)
V
clamp(SNSFB)
V
SNSFB
I
clamp(SNSFB)
014aaa862
V
fmax(ss)(RFMAX)
V
fmax(fb)(RFMAX)
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 26 of 47
NXP Semiconductors
SSL4120T
Resonant power supply control IC with PFC
V
RFMAX
and V
SSHBC/EN
are of opposite polarity. At initial start-up, V
SSHBC/EN
is below
V
fmax(SSHBC)
(typ. 3.2 V), which corresponds to the maximum frequency. During start-up,
C
ss(HBC)
is charged, V
SSHBC/EN
rises and the frequency decreases. The contribution of the
soft start function is zero when V
SSHBC/EN
is above V
fmin(SSHBC)
(typ. 7.9 V).
V
SSHBC/EN
is clamped at a maximum of V
clamp(SSHBC)
(typ. 8.4 V) (frequency is at a
minimum) and at a minimum (≈ 3 V). Below V
fmax(SSHBC)
(maximum frequency), the
discharge current is reduced to a maximum-frequency soft start current of typically 5 μA
The voltage is clamped at a minimum of V
pu(EN)
(typ. 3 V). Both clamp levels are just
outside the operating area of V
fmax(SSHBC)
to V
fmin(SSHBC)
. The margins avoid frequency
disturbance during normal output voltage regulation, but ensure that overcurrent
regulation can respond quickly.
7.8.8.2 Soft start charge and discharge
At initial start-up, the soft start capacitor C
ss(HBC)
is charged to obtain a decreasing
frequency sweep from maximum to operating frequency. As well as being used to softly
start up the resonant converter, the soft start functionality is also used for regulation
purposes (such as overcurrent regulation). C
ss(HBC)
can therefore be charged or
discharged. In the case of overcurrent regulation, a continuous alternation between
charging and discharging takes place. In this way V
SSHBC/EN
can be regulated, thereby
overruling the signal from the feedback input.
The (dis-)charge current can have a high value, I
ss(hf)(SSHBC)
(typ. 160 μA), resulting in a
fast (dis-)charge, or it can have a low value I
ss(lf)(SSHBC)
(typ. 40 μA), resulting in a slow
(dis-)charge. This two-speed soft start sweep allows for a combination of a short start-up
time for the resonant converter and stable regulation loops (such as overcurrent
regulation).
The fast (dis-)charge speed is used for the upper frequency range where V
SSHBC/EN
is
below V
ss(hf-lf)(SSHBC)
(typ. 5.6 V). In the upper frequency range, the currents in the
converter do not react strongly to frequency variations.
Fig 15. Relation between SSHBC/EN voltage and frequency
f
HB
0
V
SSHBC
V
fmax,ss(RFMAX)
V
RFMAX
f
min
f
max
0
V
fmax(SSHBC)
V
fmin(SSHBC)
V
clamp(SSHBC)
V
pu(EN)
I
SNSFB
< I
fmin(SNSFB)
I
fmin(SNSFB)
< I
SNSFB
< I
fmax(SNSFB)
V
RFMAX
f
HB
V
fmax,fb(RFMAX)
014aaa863
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 27 of 47
NXP Semiconductors
SSL4120T
Resonant power supply control IC with PFC
The slow (dis-)charge speed is used for the lower frequency range where V
SSHBC/EN
is
above V
ss(hf-lf)(SSHBC)
(typ. 5.6 V). In the lower frequency range, the currents in the
converter react strongly to frequency variations.
Section 7.8.10.2
describes how the two-speed soft start function is used for overcurrent
regulation.
The soft start capacitor is neither charged nor discharged during non-operation time in
Burst mode. The soft start voltage will not change during this time.
7.8.8.3 Soft start reset
Some protection functions, such as overcurrent protection, require fast correction of the
operating frequency set point, but do not require switching to stop. See the protection
overview in Section 7.9
for details on which protection functions use this step to the
maximum frequency. The SSL4120T has a special fast soft start reset feature for the HBC
controller that forces V
fmax(ss)(RFMAX)
on pin RFMAX. Soft start reset is also used when the
HBC controller is enabled via the SSHBC/EN pin or after a restart to ensure a safe start at
maximum frequency. Soft start reset is not used when the operation was stopped in Burst
mode.
When a protection function is activated, the oscillator control input is disconnected from
the soft start capacitor, C
ss(HBC)
, connected between pin SSHBC/EN and ground and the
switching frequency is immediately set to a maximum. Setting the switching frequency to
a maximum will restore safe switching operation in most cases. At the same time, the
capacitor is discharged to the maximum frequency level, V
fmax(SSHBC)
. Once V
SSHBC/EN
has reached this level, the oscillator control input is connected to the pin again and the
normal soft start sweep follows. Figure 16
shows the soft start reset and the two-speed
frequency sweep downwards.
Fig 16. Soft start reset and two-speed soft start
Protection
0
V
fmax(SSHBC)
V
SSHBC/EN
V
fmin(SSHBC)
0
f
min
f
HB
f
max
t
off
on
f
max
forced
fast
sweep
slow sweep regulationregulation
V
ss(hf-lf)(SSHBC)
014aaa864
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P27P28-P30P31-P33P34-P36P37-P39P40-P42P43-P45P46-P47

SSL4120T/1,518

Mfr. #:
Buy SSL4120T/1,518
Manufacturer:
NXP Semiconductors
Description:
Display Drivers & Controllers Resonant powersupply controller with PFC
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