LD7120

7

Leadtrend Technology Corporation

LD7120-DS-05 February 2005

LGATE

PHASE

UGATE

BOOT

VCC

Vin

LD7120

Vout

Vcc

Q1

Q2

Cboot

0.1uF

D1

1uF

1

2

8

4

Fig. 9

Layout Consideration

Layout is very important in high switching convert design.

There are two sets of critical components in DC/DC

converter using LD7120.The switching components are the

most critical because they switch large amount of energy,

and therefore tend to generate large amount of noise. Next

are the small signal components, which connect to sensitive

nodes, or those supplying critical bypass current and signal

coupling. Care should be taken to separate these two sets

of components and their associated grounds. Below are

some guidelines for PCB layout while using LD7120.

1.

Keep the bypass capacitor 1

µF very close to IC.

2.

Keep output voltage feed back network, FB pin and

OCSET

pin

related

components

(small

signal

components) very close to IC.

3.

Signal ground plane of FB and OCSET pin (small signal

components) should be connected to the power ground

plane with a via or only one point to minimize the effect

of power ground currents.

4.

Switching node such as BOOT, UGATE, PHASE and

LGATE should be kept as small as possible and routed

away from FB and OCSET pin.

5.

The PCB traces carrying discontinuous currents and

any high current path should be made as short and

wide as possible.

6.

If possible, a multi-layer PCB is recommended. Please

refer to the EV kit of LD7120 for a PCB layout example.