PFS7323L datasheet(18/30 Pages) POWERINT

18 / 30 page

Rev. D 06/15

PFS7323-7329

www.power.com

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.

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

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.

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.

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