RT6908 datasheet(21/22 Pages) RICHTEK

21 / 22 page

RT6908

DS6908-01

March 2013

www.richtek.com

is a registered trademark of Richtek Technology Corporation.

Layout Consideration

For high frequency switching power supplies, the PCB

layout is important to get good regulation, high efficiency

and stability. The following descriptions are the guidelines

for better PCB layout.

For good regulation, place the power components as

close as possible. The traces should be wide and short

enough especially for the high current loop.

The compensation circuit should be kept away from

the power loops and be shielded with a ground trace to

prevent any noise coupling.

Minimize the size of all LX nodes and keep them wide

and shorter.

The exposed pad of the chip should be connected to a

strong ground plane for maximum thermal consideration.

Figure 5. Derating Curve for the RT6908 Package

0.0

0.4

0.8

1.2

1.6

2.0

2.4

2.8

3.2

100

125

Ambient Temperature (°C)

Four-Layer PCB

Figure 6. PCB Layout Guide

AGND

C19

C11

C13

VI/O

VIN

PGND

R38

C28

AGND

AVDD

C24

PGND

R23

C25

C26

VCORE

R11

R12

AGND

C12

C20

Place the power components as

close as possible. The traces should

be wide and short especially for the

high-current loop.

The exposed pad of the chip

should be connected to ground

plane for thermal consideration.

Separate power ground (PGND) and analog ground

(AGND). Connect the AGND and the PGND islands

at a single end. Make sure that there are no other

connections between these separate ground planes.

The power ground (PGND) consists of input and output

capacitor grounds, the components's ground of charge

pump. The PGND should be wide and short enough to

connect to a ground plane.

Place the power components

as close as possible.

The compensation circuit should be

kept away from the power loops and

should be shielded with a ground

trace to prevent any noise coupling.

Place the power components as close as

possible. The traces should be wide and

short especially for the high current loop.

The compensation circuit

should be kept away from the

power loops and should be

shielded with a ground trace

to prevent any noise coupling.

VIN

C54

C21

PGND

RSTB

COMP1

LXI

AVDD

VDET

SDA

SCL

FBB1

BOOT2

DHB2

DRVN

CRST

COMP2

FBB2

DLB2

ILIMIT2

LXB2

PGND

VIN

curve in Figure 5 allows the designer to see the effect of

rising ambient temperature on the maximum power

dissipation.

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