SC1566IM datasheet(6/9 Pages) SEMTECH

6 / 9 page

ã 2001 Semtech Corp.

www.semtech.com

SC1566

POWER MANAGEMENT

Introduction

The SC1566 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 and

typically does not require a heatsink. Additional features

include an enable pin to allow for a very low power

consumption standby mode, and a fully adjustable

output (5-pin versions).

Component Selection

Input capacitor: a 4.7µF or 10µF ceramic capacitor is

recommended. This allows for the device being 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 22µF,

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 ceramic

output capacitors, the SC1566 is extremely tolerant of

output capacitor ESR values and thus will also work

comfortably with tantalum output capacitors.

Applications Information

External voltage selection resistors (5-pin parts): the

use of 1% resistors, and designing for a current flow

³ 10µA is recommended to ensure a well regulated

output (thus R2 £ 120kW).

Thermal Considerations

The power dissipation in the SC1566 is approximately

equal to the product of the output current and the input

to output voltage differential:

()

VOUT

VIN

•

−

≈

The absolute worst-case dissipation is given by:

(

)

MAX

(

)

MAX

(

)

MAX

(

)

MIN

(

)

MAX

(

)

MAX

(

VIN

VOUT

VIN

•

−

For a typical scenario, V

IN = 3.3V ± 5%, VOUT = 2.8V and

O = 2.5A, therefore:

IN(MAX) = 3.465V, VOUT(MIN) = 2.744V and IQ(MAX) = 1.75mA,

Thus P

D(MAX) = 1.81W.

Using this figure, and assuming T

A(MAX) = 85°C, we can

calculate the maximum thermal impedance allowable to

maintain T

J £ 150°C (see page 7):

Typical Characteristics (Cont.)

Quiescent Current vs.

Junction Temperature

Off-State Quiescent Current vs.

Junction Temperature

600

610

620

630

640

650

660

670

680

690

700

-50

-25

100

125

150

TJ (°C)

VIN = 3.3V

-50

-25

100

125

150

TJ (°C)

VIN = 5.5V

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