33710 datasheet(12/17 Pages) FREESCALE

12 / 17 page

Analog Integrated Circuit Device Data

Freescale Semiconductor

34710

TYPICAL APPLICATIONS

pcb traces short and wide helps prevent the converter's high

di/dt switching transients from causing EMI/RFI.

Figure 5. Typical PCB Layout

Figure 5 shows a typical layout for the pcb traces

connecting the IC's switching terminal (VSWITCH) and the

power inductor, rectifier, and filter components.

Also, it is recommended to design the component layout

so that the switching currents can be immediately sunk into a

broad full-plane ground that provides terminations physically

right at the corresponding component leads. This helps

prevent switching noise from propagating into other sections

of the circuitry.

Figure 6. Bottom Copper Layout

Figure 6 illustrates a pcb typical bottom copper layout for

the area underneath a buck converter populated on the top of

the same section of pcb.

The ground plane is highlighted so the reader may note

how the ground plane has been kept as broad and wide as

possible. The square vias in the plane are located to provide

an immediate path to ground from the top copper circuitry.

Figure 7. Top Copper Layout

Figure 7 shows the corresponding top copper circuit area

with the component placement.

Again, the ground plane and the vias have been

highlighted so the reader may note the proximity of these

current sink pathways to the key converter components. It is

also important to keep the power planes of the switching

converter's output spread as broad as possible beneath the

passive components, as this helps reduce EMI/RFI and the

potential for coupling noise transients into adjacent circuitry.

Figure 8. Output Plane of Buck Converter

Figure 8 shows the output plane of the buck converter

highlighted.

33710 Datasheet(PDF) 12 Page - Freescale Semiconductor, Inc