MSS5121 datasheet(22/34 Pages) MICROCHIP

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MCP16321/2

DS22285A-page 22

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 CIN placement.

CIN supplies current to the input of the circuit when the

switch is turned on. In addition to supplying high-

frequency switch current, CIN 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 VIN pin of the

MCP16321/2 device. In Figure 5-1, CIN is placed close

to the VIN 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 COUT and L

while strategically placing the COUT return close to CIN

return. Next, CBOOST should be placed between the

boost pin and the switch node pin. This leaves space

close to the MCP16321/2 VFB pin to place RTOP and

RBOT. RTOP and RBOT are routed away from the switch

node so noise is not coupled into the high-impedance

VFB input.

FIGURE 5-1:

Recommended Layout.

VOUT

GND

CIN

COUT

RBOT RTOP

RPG

CBOOST

Bottom layer is ground plane

Trace on

bottom layer

CIN

VIN

MCP16321/2

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