© 2000 SEMTECH CORP.

652 MITCHELL ROAD NEWBURY PARK CA 91320

400mA SmartLDO

MOSFET

SC1532

January 3, 2000

1

TEL:805-498-2111 FAX:805-498-3804 WEB:http://www.semtech.com

DESCRIPTION

Intended for applications such as Power Managed PCI,

the SC1532 is designed to maintain a glitch-free 3.3V

output when at least one of two inputs, 5V (VIN1) and

3.3V (VIN2), is present.

The SC1532 combines a 5V to 3.3V linear regulator

with an integral 3.3V bypass switch, along with logic

and detection circuitry to control which supply provides

the power for the output.

Whenever VIN1 exceeds a predetermined threshold

value, the internal 3.3V PMOS linear regulator is en-

abled, and the internal pass NMOS is turned off.

When VIN1 falls below a lower threshold value, the

NMOS pass device is turned on and the PMOS linear

regulator is turned off. This ensures an uninterrupted

3.3V output even if VIN1 falls out of specification.

When both supplies are simultaneously available, the

PMOS linear regulator will be turned on, and the

NMOS pass will be turned off, thus preferentially sup-

plying the output from the 5V supply.

The internal 5V detector has its upper threshold (for

VIN1 rising) set to 4.18V (typical) while the lower

threshold (for VIN falling) is at 4.1V (typical) giving a

hysteresis of approximately 80mV.

The SC1532 is available in the popular SO-8 surface

mount package.

FEATURES

APPLICATIONS

ORDERING INFORMATION

Part Number

(1)

Package

SC1532CS

SO-8

Note:

(1) Add suffix ‘TR’ for tape and reel packaging.

TYPICAL APPLICATION CIRCUIT

3.3VAUX IN

5V IN

3.3V OUT

U1

SC1532

1

2

3

4

5

6

7

8

VIN2

VIN1

VO

CP

GND

GND

GND

GND

C4

1nF

C1

4.7uF

C2

4.7uF

C3

4.7uF

NOTES:

(1) Ceramic capacitors are recommended - see Applications Information for further details.

(2) Output capacitor C3 needs to be 1.0uF or greater for stability. Additional capacitance (tantalum or ceramic) will

improve overall performance.