PFS704 POWERINT [Power Integrations, Inc.], PFS704 Datasheet - Page 6

• Manufacturer Part Number: PFS704
• Description: High Power PFC Controller with Integrated High-Voltage MOSFET
• Manufacturer: POWERINT [Power Integrations, Inc.]

Figure 6.
NPN and PNP transistor are tied between the output voltage
divider resistors to limit the maximum overshoot and under-
shoot during a load transient response. To reduce switch and
output diode current stress at start-up, the HiperPFS slews the
internal error-voltage from zero to its steady-state value at
start-up. Figure 6 illustrates the relative relationship between
the application of V
the internal error-voltage.
The error-voltage has a controlled slew rate of 0.25 V/ms at
start-up, corresponding to the t
error voltage of 5 V.
The beginning of soft-start is gated by the V
FEEDBACK pin voltage thresholds in the sequence described
below. Once the applied V
sensed V pin current is above I
is above FB
VOLTAGE MONITOR pin and checks that the FEEDBACK pin
voltage is still above the FB
that the FEEDBACK and V pins are not shorted together. In the
event that the FEEDBACK pin voltage is below the FB
Rev. D 12/11
Figure 5.
1.2
0.8
0.6
0.4
0.2
6
1
0
0
Typical Normalized Output Voltage Characteristics as Function of
Normalized Peak Load Rating
Power Limit Soft-Start Function.
PFS704-729EG
OFF
~5 V
0.2
, the IC applies a ~6 mA current sink through the
Normalized to Peak Power Rating
CC
and power limit soft-start function through
0.4
CC
OFF
is above the V
0.6
threshold. This checks to ensure
UV+
SOFT
and the feedback pin voltage
time duration for a full scale
0.8
CC+
CC+
PI-5336-110810
, I
threshold, the
1
t
UV+
and
OFF
1.2
1.4
Figure 7.
threshold the V pin holds the 6 mA current sink indefinitely until
the FEEDBACK pin is above the FB
voltage is above FB
resumes with normal soft-start and operation. Figure 7
illustrates this sequence.
Timing Supervisor and Operating Frequency Range
Since the controller is expected to operate with a variable
switching frequency over the line frequency half-cycle, typically
spanning a range of 24 – 95 kHz, the controller also features a
timing supervisor function which monitors and limits the
maximum switch on-time and off-time as well as ensures a
minimum cycle off-time. The timer supervisor limits the normal
operating frequency range for loads in excess of 10% of the
device peak power rating.
Figure 8a shows the typical half-line frequency profile of the
device switching frequency as a function of input voltage at
peak load conditions. Figure 8b shows for a given line condition
the effect of EcoSmart to the switching frequency as a function
of load (PFS704-716). The switching frequency is not a function
of boost choke inductance.
EcoSmart
The PFS704-716 controllers includes an EcoSmart mode
wherein the internal error signal (V
converter output power. Since the internal error-signal is
directly proportional to the output power, this signal level is used
to set the average switching frequency as a function of output
power. The off-time integrator control reference (V
Check Open FB
Apply 0.5 µA
YES
YES
V
V
Soft-Start
Sequence
Is I
on FB to
FB
FB
Check
V
V
V
and
> FB
CC
< FB
Start-Up Sequence.
Is
CC+
Is
> I
>
UV+
OFF
OV
YES
NO
NO
NO
OFF
, the IC releases the current source and
Is V
Current Sink
Current Sink
6 mA V pin
YES
6 mA V pin
Remove
Apply
FB
> FB
E
OFF
) is used to detect the
OFF
. If the FEEDBACK pin
NO
PI-5337-110910
www.powerint.com
Slew Power-Limit
Over Soft-Start
Voltage Peak
Detect Input
OFF
Converter
Duration
Start
) is