Datasheet

MCP16331
DS20005308B-page 22  2014 Microchip Technology Inc.
5.11 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 MCP16331 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 MCP16331 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 MCP16331 circuitry.
Unstable PWM operation can result if there are
excessive transients or ringing on the V
IN
pin of the
MCP16331 device. In
Figure 5-1, C
IN
is placed close to
pin 5. A ground plane on the bottom of the board
provides a low resistive and inductive path for the
return current. The next priority in placement is the
freewheeling current loop formed by D1, C
OUT
and L,
while strategically placing C
OUT
return close to C
IN
return. Next, the boost capacitor should be placed
between the boost pin and the switch node pin SW.
This leaves space close to the MCP16331 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.