Datasheet

 2014-2016 Microchip Technology Inc. DS20005308C-page 21
MCP16331
EXAMPLE 5-5:
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 the C
OUT
return
close to the 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.
V
IN
=10V
V
OUT
=5.0V
I
OUT
=0.4A
Efficiency = 90%
Total System Dissipation = 222 mW
L
DCR
=0.15
P
L
=24 mW
Diode V
F
=0.50
D=50%
P
Diode
= 125 mW
MCP16331 internal power dissipation estimate:
P
DIS
- P
L
- P
DIODE
= 73 mW

JA
=198°C/W
Estimated Junction
Temperature Rise
= +14.5°C