PFS7323-7329
During placement of components on the board, it is best to
place the VOLTAGE MONITOR pin, FEEDBACK pin and VCC
pin decoupling capacitors close to the HiperPFS-2 before the
other components are placed and routed. Power supply return
trace from the GROUND pin should be separate from the trace
connecting the feedback circuit components to the GROUND
pin. To minimize effect of trace impedance affecting regulation,
output feedback should be taken directly from the output
capacitor positive terminal. The upper end of the line-sense
resistors should be connected to the high frequency filter
capacitor connected at the output of the bridge rectifier.
vicinity of the probe tip can be seen. This ring is at ground
potential and the best ground connection point for making
noise free measurements. Wrapping stiff wire around the
ground ring and then connecting that ground wire into the
circuit with the shortest possible wire length, and connecting
the probe tip to the point being measured, ensures error-free
measurement. Probe should be compensated according to
probe manufacturers guidelines to ensure error-free
measurement.
2. Maximum drain current – Drain current can be measured
indirectly by monitoring inductor current. A current probe
should be inserted between the bridge rectifier and inductor
connection. At maximum ambient temperature, minimum
input voltage and maximum output load, verify inductor
current waveforms at start-up for any signs of inductor
saturation. When performing this measurement with Sendust
inductor, it is typical to see inductor waveforms that show
exponential increase in current due to permeability drop.
This should not be confused with hard saturation.
Quick Design Checklist
As with any power supply design, all HiperPFS-2 designs
should be verified on the bench to make sure that component
specifications are not exceeded under worst-case conditions.
The following minimum set of tests is strongly recommended:
1. Maximum drain voltage – verify that peak VDS does not
exceed 530 V at lowest input voltage and maximum
overload output power. Maximum overload output power
occurs when the output is overloaded to a level just above
the highest rated load or before the power supply output
voltage starts falling out of regulation. Additional external
snubbers should be used if this voltage is exceeded. In
most designs, addition of a ceramic capacitor in the range of
33 pF and 100 pF connected across the PFC output diode
will reduce the maximum drain-source voltage to a level
below the BVDSS rating. When measuring drain-source
voltage of the MOSFET, a high voltage probe should be
used. When the probe tip is removed, a silver ring in the
3. Thermal check – at maximum output power, minimum input
voltage and maximum ambient temperature; verify that
temperature specifications are not exceeded for the HiperPFS-2,
PFC inductor, output diodes and output capacitors. Enough
thermal margin should be allowed for the part-to-part
variation of the RDS(ON) of HiperPFS-2, as specified in the
data sheet. A maximum package temperature of 100 °C
under worst-case operating conditions is recommended to
allow for these variations.
4. Input PF should improve with load, if performance is found
to progressively deteriorate with loading then that is a sign of
possible noise pickup by the VOLTAGE MONITOR pin circuit
or the feedback divider network and the compensation circuit.
18
Rev. B 06/13
www.powerint.com
POWERINT [ Power Integrations ]
