1
LT1575/LT1577
Ultrafast Transient Response,
Low Dropout Regulators
Adjustable and Fixed
TYPICAL APPLICATION
1
2
3
4
8
7
6
5
SHDN
V
IN
GND
OUT
IPOS
INEG
GATE
COMP
C2
1礔
C5
220礔
5V
GND
1575/77 TA01
V
OUT
3.3V
5A
R2
5&
R1
7.5k
12V
LT1575-3.3
C4
1000pF
FOR T > 45癈:
C6 = 24 ?1礔 X7R
CERAMIC SURFACE
MOUNT CAPACITORS.
PLACE C6 IN THE
MICROPROCESSOR
SOCKET CAVITY
FOR T < 45癈:
C6 = 24 ?1礔 Y5V
CERAMIC SURFACE
MOUNT CAPACITORS.
*
Q1
IRFZ24
+
C3
10pF
C6*
24礔
Ultrafast Transient Response 5V to 3.3V Low Dropout Regulator
(For Schematic Including Current Limit, See Typical Applications)
50mV/DIV
2A/DIV
100祍/DIV
1575/77 TA02
Transient Response for
0.2A to 5A Output Load Step
s
Pentium
?/DIV>
Processor Supplies
s
PowerPC
TM
Supplies
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.
APPLICATIONS
DESCRIPTION
s
UltraFast
TM
Transient Response Eliminates
Tantalum and Electrolytic Output Capacitors
s
FET R
DS(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
FEATURES
The LT
?/DIV>
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 R
DS(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.
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.