ADD5207

Data Sheet

Rev. A | Page 14 of 16

The grounds of the IC, input capacitors, output capacitors, and

output diode (if applicable), should be connected close together,

and directly to a ground plane. It is also a good idea to have a

ground plane on both sides of the PCB. This reduces noise by

reducing ground loop errors and by absorbing more of the EMI

radiated by the inductor.

For multilayer boards of more than two layers, a ground plane

can be used to separate the power plane (power traces and com-

ponents) and the signal plane (feedback, compensation, and

components) for improved performance. On multilayer boards,

the use of vias is required to connect traces and different planes.

If a trace needs to conduct a significant amount of current from

one plane to the other, it is good practice to use one standard

via per 200 mA of current. Arrange the components so that the

switching current loops curl in the same direction.

Due to how switching regulators operate, there are two power

states: one state when the switch is on, and one when the switch

is off. During each state, there is a current loop made by the

power components currently conducting. Place the power

components so that the current loop is conducting in the same

direction during each of the two states. This prevents magnetic

field reversal caused by the traces between the two half cycles

and reduces radiated EMI.

Layout Procedure

To achieve high efficiency, good regulation, and stability, a good

PCB layout is required. It is recommended that the reference

board layout be followed as closely as possible because it is

already optimized for high efficiency and low noise.

Use the following general guidelines when designing PCBs:

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SW and GND leads as short as possible.

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Keep high current traces as short and as wide as possible.

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Keep nodes connected to SW away from sensitive traces,

such as COMP, to prevent coupling of the traces. If such

traces must be run near each other, place a ground trace

between the two as a shield.

•

Place the compensation components as close as possible to

the COMP pin.

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Place the LED current setting resistors as close as possible

to each pin to prevent noise pickup.

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Avoid routing noise-sensitive traces near high current

traces and components, especially the LED current setting

•

Use a thermal pad size that is the same dimension as the

exposed pad on the bottom of the package.

Heat Sinking

When using a surface-mount power IC or external power

switches, the PCB can often be used as the heat sink. This is

done by using the copper area of the PCB to transfer heat from

the device. Users should maximize this area to optimize thermal

performance.