LT1575/LT1577
Ultrafast Transient Response,
Low Dropout Regulators
Adjustable and Fixed
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DESCRIPTION
FEATURES
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UltraFastTM Transient Response Eliminates
Tantalum and Electrolytic Output Capacitors
FET RDS(ON) Defines Dropout Voltage
1% Reference/Output Voltage Tolerance Over
Temperature
Typical Load Regulation: 1mV
High Side Sense Current Limit
Multifunction Shutdown Pin with Latchoff
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.
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APPLICATIONS
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Pentium® Processor Supplies
PowerPCTM Supplies
5V to 3.XXV or 3.3V to 2.XXV Microprocessor Supplies
GTL Termination
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
The LT1575/LT1577 achieve unprecedented transientload 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 accommodate 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 protection, thermal shutdown or a combination of these functions. 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.
Consult factory for additional output voltage combinations available
in the LT1577.
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TYPICAL APPLICATION
Transient Response for
0.2A to 5A Output Load Step
Ultrafast Transient Response 5V to 3.3V Low Dropout Regulator
(For Schematic Including Current Limit, See Typical Applications)
LT1575-3.3
12V
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* 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
2
SHDN
C2
VIN
1µF 3
GND
4
OUT
IPOS
INEG
GATE
COMP
C3
10pF
8
+
7
6
5
R2
5Ω
R1
7.5k
C4
1000pF
Q1
IRFZ24
5V
50mV/DIV
C5
220µF
VOUT
3.3V
5A
2A/DIV
C6*
24µF
GND
1575/77 TA01
100µs/DIV
1575/77 TA02
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