SP6656 datasheet(15/17 Pages) SIPEX

15 / 17 page

Date: 7/9/04

SP6656 High Efficiency 400mA Synchronous Buck Regulator with Bit Programmable Output

APPLICATION INFORMATION

SP6656 Component Sample Layout

SP6656 PC Layout Top Side

SP6656 PC Layout Bottom Side

ground of the COUT capacitor to the ground of the

CIN capacitor and then to the PGND pin 10. The

control ground plane connects from pin 9 GND to

ground of the CVIN capacitor and the RI 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

SP6656 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 1

µF bypass capacitor as close to the VINand

GND pins of the converter as possible, the 10

µF

CIN close to the PVIN pin and the 10µF output

capacitor as close to the inductor as possible. The

external voltage feedback network RF, RI, RS and

feedforward capacitor CF 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.

SP6656 Datasheet(PDF) 15 Page - Sipex Corporation