sp6651a Exar Corporation, sp6651a Datasheet - Page 13

• Manufacturer Part Number: sp6651a
• Description: High Efficiency 800ma Synchronous Buck Regulator
• Manufacturer: Exar Corporation

Figure 21. SP6651A PCB Bottom Sample Layout
Date: 5/25/04
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
C
control ground plane connects from pin 9 GND to
ground of the C
return of the feedback resistor. These two separate
control and power ground planes come together in
the figure titled PCB top sample layout where
Figure 19. SP6651A PCB Component Sample Layout
IN
capacitor and then to the PGND pin 10. The
OUT
VIN
capacitor to the ground of the
capacitor and the R
SP6651A High Efficiency 800mA Synchronous Buck Regulator
I
ground
13
APPLICATION INFORMATION: Continued
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
GND pins of the converter as possible, the 22µF
C
capacitor as close to the inductor as possible. The
external voltage feedback network R
feedforward capacitor C
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.
Figure 20. SP6651A PCB Top Sample Layout
IN
close to the P
VIN
pin and the 22µF output
© Copyright 2004 Sipex Corporation
F
should be placed very
F
, R
IN
I
and
and