LT1575/LT1577
Ultrafast Transient Response,
Low Dropout Regulators
Adjustable and Fixed
FEATURES
s UltraFastTM Transient Response Eliminates
Tantalum and Electrolytic Output Capacitors
s FET RDS(ON) Defines Dropout Voltage
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
U
APPLICATIONS
s Pentium® Processor Supplies
s PowerPCTM Supplies
s 5V to 3.XXV or 3.3V to 2.XXV Microprocessor Supplies
s GTL Termination
s Low Voltage Logic Supplies
LT1575CN8/LT1575CS8
LT1575CN8-1.5/LT1575CS8-1.5
LT1575CN8-2.8/LT1575CS8-2.8
LT1575CN8-3.3/LT1575CS8-3.3
LT1575CN8-3.5/LT1575CS8-3.5
LT1575CN8-5/LT1575CS8-5
LT1577CS-ADJ/ADJ
LT1577CS-3.3/ADJ
LT1577CS-3.3/2.8
Adjustable
1.5V Fixed
2.8V Fixed
3.3V Fixed
3.5V Fixed
5V Fixed
Adjustable, Adjustable
3.3V Fixed, Adjustable
3.3V Fixed, 2.8V Fixed
Consult factory for additional output voltage combinations available
in the LT1577.
DESCRIPTION
The LT®1575/LT1577 are single/dual controller ICs that
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.
Selection of the N-channel MOSFET RDS(ON) allows very
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.
, LTC and LT are registered trademarks of Linear Technology Corporation.
UltraFast is a trademark of Linear Technology Corporation.
Pentium is a registered trademark of Intel Corporation.
PowerPC is a trademark of IBM Corporation.
TYPICAL APPLICATION
Ultrafast Transient Response 5V to 3.3V Low Dropout Regulator
(For Schematic Including Current Limit, See Typical Applications)
*FOR T < 45°C:
C6 = 24 × 1µF Y5V
CERAMIC SURFACE
MOUNT CAPACITORS.
FOR T > 45°C:
C6 = 24 × 1µF X7R
CERAMIC SURFACE
MOUNT CAPACITORS.
PLACE C6 IN THE
MICROPROCESSOR
SOCKET CAVITY
12V
1
2
C2
1µF 3
4
LT1575-3.3
SHDN IPOS
VIN INEG
GND GATE
OUT COMP
8
7
6
5
R2
5Ω
C3
10pF
R1
7.5k
C4
1000pF
+
Q1
IRFZ24
5V
C5
220µF
C6*
24µF
VOUT
3.3V
5A
GND
1575/77 TA01
Transient Response for
0.2A to 5A Output Load Step
50mV/DIV
2A/DIV
100µs/DIV
1575/77 TA02
1
