MCP16331 datasheet(23/48 Pages) MICROCHIP

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DS20005308D-page 23

MCP16331

EXAMPLE 5-5:

5.11

PCB Layout Information

Good printed circuit board layout techniques are

important to any switching circuitry and switched-mode

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 the COUT return

close to the 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.

VIN =10V

VOUT =5.0V

IOUT =0.4A

Efficiency = 90%

Total System Dissipation = 222 mW

LDCR =0.15

PL =24 mW

Diode VF =0.50

D=50%

PDiode = 125 mW

MCP16331 internal power dissipation estimate:

PDIS – PL – PDIODE = 73 mW

JA =198°C/W

Estimated Junction

Temperature Rise

= +14.5°C

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