MC34710 Datasheet, PDF (12/18 Pages) Motorola, Inc – Adjustable Dual Output Switching Power Supply

TYPICAL APPLICATIONS
short and wide helps prevent the converter's high di/dt
switching transients from causing EMI/RFI.
possible. The square vias in the plane are located to provide
an immediate path to ground from the top copper circuitry.
Figure 5. Typical PCB Layout
Figure 5 shows a typical layout for the pcb traces
connecting the IC's switching pin (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 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 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
Figure 8. Output Plane of Buck Converter
Figure 8 shows the output plane of the buck converter
highlighted.
34710
12
Analog Integrated Circuit Device Data
Freescale Semiconductor