IRU3048

11

Rev. 1.7

09/12/02

www.irf.com

Layout Consideration

The layout is very important when designing high fre-

quency switching converters. Layout will affect noise

pickup and can cause a good design to perform with

less than expected results.

Start to place the power components, make all the con-

nection in the top layer with wide, copper filled areas.

The inductor, output capacitor and the MOSFET should

be close to each other as possible. This helps to reduce

the EMI radiated by the power traces due to the high

switching currents through them. Place input capacitor

directly to the drain of the high-side MOSFET, to reduce

the ESR replace the single input capacitor with two par-

allel units. The feedback part of the system should be

kept away from the inductor and other noise sources,

and be placed close to the IC. In multilayer PCB use

one layer as power ground plane and have a control cir-

cuit ground (analog ground), to which all signals are ref-

erenced. The goal is to localize the high current path to

a separate loop that does not interfere with the more

sensitive analog control function. These two grounds

must be connected together on the PC board layout at a

single point.

TYPICAL APPLICATION

12V to 3.3V @ 4A

12V to 1.8V @ 4A

3.3V to 2.5V @ 2A

Figure 8 - Typical application of IRU3048 in an on-board DC-DC converter

using a single 12V supply for switcher.

12V

2.5V @ 2A

C9

47uF

R7

1K

1/2 of Q3

IRF7313

L4

1/2 of Q3

IRF7313

C8

1uF

C15

47uF

3.3V

U1

3.3V @ 4A

R8

1K

C13

1uF

L3

C16

47uF

R6

1.65K

C24

0.1uF

R5

R11

C19

R9

C18

C1

1uF

PGnd

LDrv1

HDrv1

Fb1

LDrv2

HDrv2

VcH1

VcH2

Vcc

Gnd

Comp2

Fb3

Comp1

SS

IRU3048

1/2 of Q2

IRF7313

1/2 of Q2

IRF7313

C6

47uF

C3

0.1uF

10uH

6.8uH

1.8V @ 4A

R15

1K

R14

442

V

Fb2

1K

Q1

IRLR2703

L1

1uH

C2

33uF

D1

BAT54S

C14

1uF

R2

10

V

C7

1uF

C17

1uF

C10

470pF

R4

4.7

V

C20

470pF

R13

4.7

V

C11, C12

2x 150uF

1800pF

3900pF

43.2K

16.2K

C21, C22

2x 150uF

C23

1uF