PFS7323-7329
which is essential to meet many efficiency directives. The
degree of frequency slide is also controlled as a function of
peak input line voltage, at high input line the maximum off-time
voltage reference at zero error-voltage will be approximately 1/4
of the maximum value at low input line conditions.
threshold when the power good signal transitions from the ‘on’
state to the high-impedance high-state as the PFC output
voltage falls out of regulation.
The POWER GOOD THRESHOLD pin has an internal 100 ms
de-glitch filter (tPG) to prevent noise events from falsely setting
the VPG(L) threshold.
The lower VOFF slope reduces the average frequency swing for
high input line operation.
In the event a load fault prevents the boost from achieving
regulation (~95% of the set output voltage threshold) the PG
function will remain in the high-impedance state and will not
annunciate when a output voltage has fallen below the user
programmed VPG(L) threshold.
Burst-Mode for No-Load Power Consumption Reduction
Unlike the original HiperPFS which had the ability to reduce the
minimum on-time to zero, the minimum on-time in HiperPFS-2
has a minimum value of 500 ns to enable burst-mode operation
at no-load.
The VPG(L) user programmed threshold is enabled once VPG(H)
threshold has been reached.
Since the minimum on-time is 500 ns, at no-load the output
voltage will climb until the device shuts off due to the voltage on
the COMPENSATION pin reaching the COV threshold. The
output voltage ripple at no-load to light load will be increased as
a result of the burst-mode operation.
If the PGT programming resistor is left open, the power good
function is disabled and remains in the high-impedance (‘off’)
state, whereas if the POWER GOOD THRESHOLD pin is
shorted to the GROUND pin the power good signal will remain
in the low (‘on’) state until the PFC output voltage has fallen to
the CUV threshold.
A higher minimum on-time and inclusion of the COV comparator
are the main elements in the design to enable this burst-mode
operation at no-load. The burst-mode was added to reduce the
power stage no-load consumption to below 0.5 W when the
boost converter is designed with a ferrite boost choke.
Similar to the condition described above, if the value of the PGT
resistor is such that the VPG(L) threshold is greater than the VPG(H)
threshold the PG signal will remain in the high-impedance off-
state.
Power Good Signal (PG)
The HiperPFS-2 features a ‘power good’ (PG) circuit which
comprises of an internal comparator that at start-up turns ‘on’ a
switch when the sensed output voltage on the FEEDBACK pin
rises to ~95% (VPG(H) threshold) of the set output voltage threshold.
During start-up prior to the output voltage reaching VPG(H) the PG
signal is in a high-impedance state (internal switch is in ‘off’ state).
Power good function is not valid under the following conditions:
A. VCC is not in a valid range. Below VCC-, the power good
function is not valid.
B. REFERENCE pin resistor is in an invalid range. If the
REFERENCE pin resistor is not either 24. 9 kW for ‘Full’ or
49.9 kW for ‘Efficiency’ mode, the power good signal is not
valid. Power good will go to high-impedance state (internal
MOSFET is ‘off’) at the end of the fast soft-shutdown initiated
by the REFERENCE pin resistor fault.
C. The valid programming range of PGT is between 275 V to
360 V. Programming an output voltage below 275 VDC to
trigger PG is invalid.
When the AC input voltage is removed or other fault occurs
after start-up, the power good signal transitions from ‘on’ to ‘off’
state once the sensed output voltage on the FEEDBACK pin
falls to a user selected threshold programmed with a resistor on
the POWER GOOD THRESHOLD pin. The POWER GOOD
THRESHOLD pin has a fixed source current of IPGT and this
combined with the power good threshold resistor sets the
Set internally
100% VOUT (380 V)
by VPG(H)
95% VOUT (361 V)
Output Voltage
Rising
Set externally
by RPG
87.5% VOUT (333 V)
0.875 # VREF
IPG
5.25 V
50 nA
RPG
=
=
= 105 kX
Output Voltage
Falling
tPG
tPG
PG = High Impedance
PG = On-State
PG = High Impedance
PI-6700-040512
Figure 11. Power Good Function Description.
8
Rev. B 06/13
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