MCP16311SLASH2 datasheet(23/40 Pages) MICROCHIP

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DS20005255C-page 23

MCP16311/2

5.11

Printed Circuit Board (PCB)

Layout Information

Good PCB 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 MCP16311/2 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 MCP16311/2 layout starts with the placement of

the input capacitor, which supplies current to the input

of the circuit when the switch is turned on. In addition to

supplying high-frequency switch current, the input

capacitor also provides a stable voltage source for the

internal

MCP16311/2

circuitry.

Unstable

PWM

operation can result if there are excessive transients or

ringing on the VIN pin of the MCP16311/2 device. In

Figure 5-1, the input capacitors are 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 output capacitors

and inductance (L1), while strategically placing the

output capacitor ground return close to the input

capacitor ground return. Then, CBOOST should be

placed between the boost pin and the switch node pin.

This leaves space close to the MCP16311/2 VFB pin to

place RTOP and RBOT. The feedback loop must be

routed away from the switch node, so noise is not

coupled into the high-impedance VFB input.

FIGURE 5-1:

MSOP-8 Recommended Layout, 5V Output Design.

VIN

GND

VFB

VIN

12V

VOUT

5V @ 1A

COUT

CIN

VCC

CVCC

CBOOST

BOOST

REN

Component

Value

CIN

2 x 10 µF

COUT

2 x 10 µF

22 µH

52.3 k



10 k



REN



CVCC

1µF

CBOOST

0.1 µF

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