© 2000 SEMTECH CORP.

652 MITCHELL ROAD NEWBURY PARK CA 91320

VERY LOW DROPOUT 1.5 AMP

REGULATOR WITH ENABLE

SC1565

October 3, 2000

7

TYPICAL CHARACTERISTICS (Cont.)

0

1

2

3

4

5

6

7

8

9

10

-50

-25

0

25

50

75

100

125

150

VIN = 5.5V

Off-State Quiescent Current vs.

Junction Temperature

500

510

520

530

540

550

560

570

580

590

600

-50

-25

0

25

50

75

100

125

150

VIN = 3.3V

Quiescent Current vs.

Junction Temperature

APPLICATIONS INFORMATION

Introduction

The SC1565 is intended for applications such as

graphics cards where high current capability and very

low dropout voltage are required. It provides a very

simple, low cost solution that uses very little pcb real

estate. Additional features include an enable pin to al-

low for a very low power consumption standby mode,

and a fully adjustable output.

Component Selection

Input capacitor - a 4.7µF ceramic capacitor is recom-

mended. This allows for the device being some dis-

tance from any bulk capacitance on the rail. Addition-

ally, input droop due to load transients is reduced, im-

proving load transient response. Additional capaci-

tance may be added if required by the application.

Output capacitor - a minimum bulk capacitance of

10µF, along with a 0.1µF ceramic decoupling capacitor

is recommended. 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 ce-

ramic output capacitors, the SC1565 is extremely toler-

ant of output capacitor ESR values and thus will also

work comfortably with tantalum output capacitors.

External voltage selection resistors - the use of 1% re-

sistors, and designing for a current flow

≥ 10µA is rec-

ommended to ensure a well regulated output (thus R2

≤ 120kΩ).

Thermal Considerations

The power dissipation in the SC1565 is approximately

equal to the product of the output current and the input

to output voltage differential:

The absolute worst-case dissipation is given by:

For a typical scenario, VIN = 3.3V ± 5%, VOUT = 2.8V

and I

VIN

I

Thus P

Using this figure, and assuming T

calculate the maximum thermal impedance allowable

to maintain T

This should be achievable for the SO-8 package using

pcb copper area to aid in conducting the heat away,

such as one square inch of copper connected to the

ground pins of the device. The SOT-223 and TO-220

packages would not require heatsinking. Internal

ground/power planes and air flow will also assist in re-

moving heat. For higher ambient temperatures it may

be necessary to use additional copper area.

()

O

D

I

VOUT

VIN

P

•

−

≈

(

)

)

MAX

(

Q

)

MAX

(

)

MAX

(

O

)

MIN

(

)

MAX

(

)

MAX

(

D

I

VIN

I

VOUT

VIN

P

•

+

•

−

=

R

TT

P

CW

TH J A MAX

JMAX

A MAX

DMAX

()(

)

()

()

()

.

./

−

=

−

=

−

=°

150

70

109

73 4