PFS7323-7329
introduces a low frequency zero required to tailor the loop
response to ensure low cross-over frequency and sufficient
phase margin. Resistor R6 isolates the fast portion (resistor
voltage divider network comprising of resistors R1 to R4) and
the slow feedback loop compensator circuit (resistor R7 and
capacitor C3). Diode D1 is included to cover a single point fault
condition wherein capacitor C3 is shorted. In the event C3 is
short-circuited, the FEEDBACK pin is forced below the FBOFF
threshold through diode D1 and subsequently turns the
HiperPFS-2 off. Only a standard recovery diode should be
used for D1. Use of ultrafast or fast recovery diode is not
recommended including small signal diodes (e.g. 1N4148),
which are typically also fast recovery.
VO - 75
R1 =
- R3
100 # 10-6
The value of resistor R7 will have to be adjusted in some
designs and as a guideline the value from the following
calculation can be used:
PO
1.2 VO CO
^
h
kX
R7 = RZ =
2
#
#
PO Maximum continuous output power in watts
VO Nominal PFC output voltage in volts
CO PFC output capacitance in farads
The recommended values for the components used are as
follows:
Improvement in low frequency phase margin can be achieved
by increasing the value of the capacitor C3 however increase in
value of capacitor C3 will result in some increase in overshoot at
the output of the PFC during transient loading and should be
verified.
R4 = 60.4 kW
R3 = 1.6 MW
R2 = 787 kW
C1 = 47nF, 200 V X7R/NPO
Heat Sinking and Thermal Design
Figure 16, 17, 18 shows examples of the recommended
assembly for the HiperPFS-2. In these assemblies as shown,
no insulation pad is required and HiperPFS-2 can be directly
connected to heat sink by clip or adhesive thermal material.
R6 = 487 kW
R7 = 7.5 kW
C3 = 2.2 mF
Cc = 22 nF
D1 = BAV116 W or 1N4007 (A general purpose standard
recovery diode should only be used).
The HiperPFS-2 back metal is electrically connected to the heat
sink and the heat sink is required to be connected to the
HiperPFS-2 source terminal in order to reduce EMI.
When the above component values are used, the value of
resistor R1 can be calculated using the following equation:
Figure 16. Heat Sink Assembly – Using Thermally Conductive Adhesive.
15
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Rev. B 06/13
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