MCP16331 datasheet(22/40 Pages) MICROCHIP

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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 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 MCP16331 circuitry.

Unstable PWM operation can result if there are

excessive transients or ringing on the VIN pin of the

MCP16331 device. In Figure 5-1, CIN 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, COUT and L,

while strategically placing COUT return close to CIN

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 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.

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