© 2000 SEMTECH CORP.

652 MITCHELL ROAD NEWBURY PARK CA 91320

700mA SmartLDO

TM

SC1537

PRELIMINARY - July 25, 2000

1

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

FEATURES

APPLICATIONS

ORDERING INFORMATION

Part Number

(1)

Package

SC1537CSTR

SO-8

SC1537CMTR

TO-263-5L

Note:

(1) Only available in tape and reel packaging. A reel con-

tains 2500 devices for SO-8 and 800 devices for TO-263.

DESCRIPTION

The SC1537 is designed to maintain a glitch-free 3.3V

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

3.3V (VAUX), is present.

Whenever VIN exceeds a predetermined threshold

value, the internal 3.3V linear regulator is enabled, and

DR is pulled high.

When VIN falls below a lower threshold value, DR is

pulled low and the internal linear regulator is turned off.

DR has been designed to drive the gate of an external

low threshold P-channel MOSFET, which can be used

to connect the 3.3V supply directly to the regulator

output. This ensures an uninterrupted 3.3V output even

if VIN falls out of specification. A maximum R

100m

Ω is recommended.

When both supplies are simultaneously available, the

drive pin (DR) will be pulled High, turning off the exter-

nal PMOS switch.

The internal 5V detector has its upper threshold (for

VIN rising) set to 4.22V (typical) while the lower thresh-

old (for VIN falling) is at 4.05V (typical) giving a hystere-

sis of approximately 170mV.

The SC1537 is available in the popular SO-8 and

5-lead TO-263 surface mount packages.

APPLICATION CIRCUIT

NOTE:

(1) External switch (Q1): use a low threshold P-channel MOSFET such as Vishay Si2305DS (R

V

3.3V OUT

3.3V

5V

5V

3.3V

3.3V OUT

C3

0.1uF

C4

10uF

C2

10uF

C5

0.1uF

Q1

C1

0.1uF

U1

SC1537CM

1

2

3

4

5

VIN

VAUX GND

VO

DR

TAB

U1 SC1537CS

1

2

3

4

5

6

7

8

VAUX

VIN

VO

DR

GND

GND

GND

GND

C2

10uF

Q1

C4

10uF

C1

0.1uF

C3

0.1uF

C5

0.1uF