12

Applications Information (continued)

SC4540

Diode Selection

A Schottky diode with a reverse voltage of 60V and a

forward current rating of 1A should be used with this

device for optimum performance. The ST Microelectronics

STPS05602 is a recommended diode for this application.

Selection of Other Components

R

ISET

sets the maximum load current for the SC4540. Use

the following equation to select the proper value:

R

ISET

= 230×V

ISET

/I

LOAD

where

V

ISET

= 0.5V (typ).

Refer to Figure 1 for selecting values for other current set-

tings. Note that the error increases as the desired I

BL

current decreases.

1

10

100

1

10

100

Typical

C urrent

T olerance

Figure 1 – Set Resistor Value Selection Graph

PCB Layout Considerations

Poor layout can degrade the performance of the DC-DC

converter and can be a contributory factor in EMI prob-

lems, ground bounce, thermal issues, and resistive voltage

losses. Poor regulation and instability can result. A typical

layout is shown in Figure 4.

The following design rules are recommended:

Place the inductor and filter capacitors as close

to the device as possible and use short, wide

traces between the power components.

Route the output voltage feedback path away

from the inductor and LX node to minimize

noise and magnetic interference.

Use a ground plane to further reduce noise

interference on sensitive circuit nodes.

Figure 4– Layout

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