PCB Layout Guide
PFC block normally handles high switching current and
the voltage low energy signal path can be affected by
the high energy path. Cautious PCB layout is mandatory
for stable operation.
5. A stabilizing capacitor for VCC is recommended as
close as possible to the VCC and ground pins. If it is
difficult, place the SMD capacitor as close to the
corresponding pins as possible.
1. The gate drive path should be as short as possible.
The closed-loop that runs from the gate driver,
MOSFET gate, and MOSFET source to ground of
PFC controller should be as close as possible. This
is also crossing point between power ground and
signal ground. Power ground path from the bridge
diode to the output bulk capacitor should be short
and wide. The sharing position between power
ground and signal ground should be only at one
position to avoid ground loop noise. Signal path of
PFC controller should be short and wide for
external components to contact.
2. PFC output voltage sensing resistor is normally
high to reduce current consumption. This path can
be affected by external noise. To reduce noise
potential at the INV pin, a shorter path for output
sensing is recommended. If a shorter path is not
possible, place some dividing resistors between
PFC output and the INV pin — closer to the INV pin
is better. Relative high voltage close to the INV pin
can be helpful.
3. ZCD path is recommended close to auxiliary
winding from boost inductor and to the ZCD pin. If
that is difficult, place a small capacitor (below 50pF)
to reduce noise.
Figure 44. Recommended PCB Layout
4. The switching current sense path should not share
with another path to avoid interference. Some
additional components may be needed to reduce
the noise level applied to the CS pin.
© 2010 Fairchild Semiconductor Corporation
FAN7930C • Rev. 1.0.0
www.fairchildsemi.com
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