1

LT1575/LT1577

Ultrafast Transient Response,

Low Dropout Regulators

Adjustable and Fixed

1

2

3

4

8

7

6

5

SHDN

GND

OUT

IPOS

INEG

GATE

COMP

C2

1

µF

C5

220

µF

5V

GND

1575/77 TA01

3.3V

5A

R2

5

Ω

R1

7.5k

12V

LT1575-3.3

C4

1000pF

FOR T > 45

°C:

C6 = 24

× 1µF X7R

CERAMIC SURFACE

MOUNT CAPACITORS.

PLACE C6 IN THE

MICROPROCESSOR

SOCKET CAVITY

FOR T < 45

°C:

C6 = 24

× 1µF Y5V

CERAMIC SURFACE

MOUNT CAPACITORS.

*

Q1

IRFZ24

+

C3

10pF

C6*

24

µF

Ultrafast Transient Response 5V to 3.3V Low Dropout Regulator

(For Schematic Including Current Limit, See Typical Applications)

50mV/DIV

2A/DIV

100

µs/DIV

1575/77 TA02

Transient Response for

0.2A to 5A Output Load Step

s

Pentium

s

PowerPC

s

5V to 3.XXV or 3.3V to 2.XXV Microprocessor Supplies

s

GTL Termination

s

Low Voltage Logic Supplies

LT1575CN8/LT1575CS8

Adjustable

LT1575CN8-1.5/LT1575CS8-1.5

1.5V Fixed

LT1575CN8-2.8/LT1575CS8-2.8

2.8V Fixed

LT1575CN8-3.3/LT1575CS8-3.3

3.3V Fixed

LT1575CN8-3.5/LT1575CS8-3.5

3.5V Fixed

LT1575CN8-5/LT1575CS8-5

5V Fixed

LT1577CS-ADJ/ADJ

Adjustable, Adjustable

LT1577CS-3.3/ADJ

3.3V Fixed, Adjustable

LT1577CS-3.3/2.8

3.3V Fixed, 2.8V Fixed

Consult factory for additional output voltage combinations available

in the LT1577.

s

UltraFast

Tantalum and Electrolytic Output Capacitors

s

s

1% Reference/Output Voltage Tolerance Over

Temperature

s

Typical Load Regulation: 1mV

s

High Side Sense Current Limit

s

Multifunction Shutdown Pin with Latchoff

FEATURES

The LT

drive low cost external N-channel MOSFETs as source

followers to produce ultrafast transient response, low

dropout voltage regulators.

The LT1575/LT1577 achieve unprecedented transient-

load performance by eliminating expensive tantalum or

bulk electrolytic output capacitors in the most demanding

modern microprocessor applications. Precision-trimmed

adjustable and fixed output voltage versions accommo-

date any required microprocessor power supply voltage.

low dropout voltages to be achieved.

Unique protection features include a high side current

limit amplifier that activates a fault protection timer

circuit. A multifunction Shutdown pin provides either

current limit time-out with latchoff, overvoltage protec-

tion, thermal shutdown or a combination of these func-

tions. The LT1575 is available in 8-pin SO or PDIP and the

LT1577 is available in 16-pin narrow body SO.

UltraFast is a trademark of Linear Technology Corporation.

Pentium is a registered trademark of Intel Corporation.

PowerPC is a trademark of IBM Corporation.

, LTC and LT are registered trademarks of Linear Technology Corporation.