RT9971 datasheet(20/22 Pages) RICHTEK

20 / 22 page

DS9971-01 April 2011

www.richtek.com

RT9971

Figure 2. PCB Layout Guide

Figure 1. Derating Curves for RT9971 Packages

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

3.0

100

125

Ambient Temperature (

°C)

WQFN-40L 5x5

Four Layers PCB

Layout Considerations

For the best performance of the RT9971, the following

PCB layout guidelines must be strictly followed.

}

Place the input and output capacitors as close as

possible to the input and output pins respectively for

good filtering.

}

Keep the main power traces as wide and short as

possible.

}

The switching node area connected to LX and inductor

should be minimized for lower EMI.

}

Place the feedback components as close as possible

to the FB pin and keep these components away from

the noisy devices.

}

Place the compensative components as close as

possible to the COMP pin and keep these components

away from the noisy devices.

}

Connect the GND and Exposed Pad to a strong ground

plane for maximum thermal dissipation and noise

protection.

The maximum power dissipation depends on operating

ambient temperature for fixed TJ(MAX) and thermal

resistance

θJA. For RT9971 packages, the Figure 1 of

derating curves allows the designer to see the effect of

rising ambient temperature on the maximum power

allowed.

LX should be connected to inductor by

wide and short trace, keep sensitive

components away from this trace.

PVDD2

VDDM

CFB7

GND

LX7

LX5

VOUT7

FB3

EN7

LX3

PVDD1

PVDD6

PNEG

FB6

FB4

EN6

LX4

GND

LX6

C 23

VBAT

C 26

C24

VBAT

C 14

C20

R15

GND

WLED+

WLED-

C10

GND

VOUT_CH3

GND

R12

C15 R11

C16

C11

GND

C 12

GND

R10

C13

C19

R14

R13

VOUT_CH4

C18

C21

GND

VOUT_CH2

C22

VBAT

VOUT_CH1

GND

Place the feedback and compensation

components as close as possible to the FB and

COMP pin and keep away from noisy devices.

Input/Output

capacitors must

be placed as close

as possible to the

Input/Output pins.

Connect the Exposed Pad

to a ground plane.

C25

VBAT

R16

C17

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