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Date: 5/25/04 SP6651A High Efficiency 800mA Synchronous Buck Regulator © Copyright 2004 Sipex Corporation
APPLICATION INFORMATION: Continued
Figure 19. SP6651A PCB Component Sample Layout Figure 20. SP6651A PCB Top Sample Layout
Figure 21. SP6651A PCB Bottom Sample Layout
between the SP6651A high frequency converter
and the other active components on the board,
some rules should be followed. Refer to the typical
application schematic on page 1 and the sample
PCB layout shown in the following figures to
illustrate how to layout a SP6651A power supply.
Avoid injecting noise into the sensitive part of
circuit via the ground plane. Input and output
capacitors conduct high frequency current through
the ground plane. Separate the control and power
grounds and connect them together at a single
point. Power ground plane is shown in the figure
titled PCB top sample layout and connects the
ground of the C
OUT
capacitor to the ground of the
C
IN
capacitor and then to the PGND pin 10. The
control ground plane connects from pin 9 GND to
ground of the C
VIN
capacitor and the R
I
ground
return of the feedback resistor. These two separate
control and power ground planes come together in
the figure titled PCB top sample layout where
SP6651A pin 9 GND is connected to pin 10
PGND.
Power loops on the input and output of the con-
verter should be laid out with the shortest and
widest traces possible. The longer and narrower
the trace, the higher the resistance and inductance
it will have. The length of traces in series with the
capacitors increases its ESR and ESL and reduces
their effectiveness at high frequencies. Therefore,
put the 1µF bypass capacitor as close to the V
IN
and
GND pins of the converter as possible, the 22µF
C
IN
close to the P
VIN
pin and the 22µF output
capacitor as close to the inductor as possible. The
external voltage feedback network R
F
, R
I
and
feedforward capacitor C
F
should be placed very
close to the FB pin. Any noise traces like the LX
pin should be kept away from the voltage feedback
network and separated from it by using power
ground copper to minimize EMI.
