SC1564

9

Applications Information

Introduction

The SC564 is intended for applications such as graph-

ics cards where high current capability and low drop-

out voltage are required. It provides a very simple, low

cost solution that uses little PCB real estate. Additional

features include a shutdown pin to allow for a very low

power consumption standby mode, and a fully adjust-

able output.

Component Selection

Input capacitor: A µF ceramic capacitor is recommended.

This allows for the device some distance from any bulk

capacitance on the rail. Additionally, input droop due

to load transients is reduced, improving load transient

response. Additional capacitance may be added if

required by the application.

Output capacitor: A minimum bulk capacitance of µF,

along with a 0.µF ceramic decoupling capacitor, is rec-

ommended. Increasing the bulk capacitance will improve

the overall transient response. The use of multiple lower

value ceramic capacitors in parallel to achieve the desired

bulk capacitance will not cause stability issues. Although

designed for use with ceramic output capacitors, the

SC564 is extremely tolerant of output capacitor ESR

values and thus will also work comfortably with tantalum

output capacitors.

Noise immunity: In very electrically noisy environents, it

is recommended that 0.µF ceramic capacitors be placed

from IN to GND and OUT to GND as close to the device

pins as possible.

External voltage selection resistors: the use of % resis-

tors, designed for a current flow

≥ 0µA is recommended

to ensure a well-regulated output (tus, R2

≤ 20kΩ).

Thermal Considerations

The power dissipation in the SC564 is approximately

equal to the product of the output current and the input

to output voltage differential:

OUT

OUT

IN

O

I

)

V

(V

P

The absolute worst-case dissipation is given by:

Q(MAX)

IN(MAX)

OUT(MAX)

OUT(MIN)

IN(MAX)

O(MAX)

I

V

I

)

V

V

(

P

⋅

+

⋅

−

=

For a typical scenario, V

I

V

V

I

Thus P

Using this figure, and assuming T

calculate the maximum thermal impedance allowable

to maintain T

W

C

54.3

1.1976W

C

85

C

150

P

T

T

R

O(MAX)

A(MAX)

J(MAX)

A)(MAX)

TH(J

This should be achievable with the 3mm x 3mm MLPD-8

package using PCB copper area to aid in conducting the

heat away from the device. Internal ground/power planes

and air flow will also assist in removing heat.