Microchip Technology ADM00423 Data Sheet

DS22285A-page 22

© 2011 Microchip Technology Inc.

5.0.9

PCB LAYOUT INFORMATION

Good printed circuit board layout techniques are
important to any switching circuitry, and switching
power supplies are no different. When wiring the
switching high-current paths, short and wide traces
should be used. Therefore, it is important that the input
and output capacitors be placed as close as possible to
the MCP16321/2 to minimize the loop area.
The feedback resistors and feedback signal should be
routed away from the switching node and the switching
current loop. When possible, ground planes and traces
should be used to help shield the feedback signal and
minimize noise and magnetic interference.
A good MCP16321/2 layout starts with C

IN

 placement.

C

IN

 supplies current to the input of the circuit when the

switch is turned on. In addition to supplying high-

frequency switch current, C

IN

 also provides a stable

voltage source for the internal MCP16321/2 circuitry.
Unstable PWM operation can result if there are
excessive transients or ringing on the V

IN

 pin of the

MCP16321/2 device. In 

IN

 is placed close

to the V

IN

 pins. A ground plane on the bottom of the

board provides a low resistive and low inductive path
for the return current. The next priority in placement is
the freewheeling current loop formed by C

OUT

 and L

while strategically placing the C

OUT

 return close to C

IN

return. Next, C

BOOST

 

should be placed between the

boost pin and the switch node pin. This leaves space
close to the MCP16321/2 V

FB

 pin to place R

TOP

 and

R

BOT

. R

TOP

 and R

BOT

 are routed away from the switch

node so noise is not coupled into the high-impedance
V

FB

 input.

V

OUT

GND

GND

C

IN

C

OUT

C

OUT

R

BOT

R

TOP

10

Ω 

R

PG

C

BOOST

Bottom layer is ground plane

Trace on

bottom layer

C

IN

V

IN

L