SP6655 Datasheet, PDF (14/16 Pages) Sipex Corporation – High Efficiency 400mA Synchronous Buck Regulator Ideal for portable designs powered with Li Ion battery

APPLICATION INFORMATION
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 SP6655 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
SP6655 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 10µF
C_IN close to the P_VIN pin and the 10µF 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.
SP6655 Component Sample Layout
SP6655 PC Layout Top Side
SP6655 PC Layout Bottom Side
Date: 7/12/04
SP6655 High Efficiency 400mA Synchronous Buck Regulator
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© Copyright 2004 Sipex Corporation