LT1573
Low Dropout
PNP Regulator Driver
FEATURES
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DESCRIPTIO
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Low Cost Solution for High Current, Low Dropout
Regulators
Fast Transient Response Needs Much Less
Bulk Capacitance
Latching Overload Protection Minimizes
Heat Sink Size
Precision Output Voltage (1%)
Single Supply Operation: V
IN
= 2.8V to 10V
Small Surface Mount Package
Capable of Very Low Dropout Voltage (<0.2V)
Fixed or Adjustable Outputs
Shutdown
The LT
®
1573 is a regulator driver IC designed to provide
a low cost solution for applications requiring high current,
low dropout and fast transient response. When combined
with an external PNP power transistor, this device pro-
vides load current up to 5A with dropout voltages as low
as 0.35V. The LT1573 circuitry is designed for extremely
fast transient response. This greatly reduces bulk storage
capacitance when the regulator is used in applications
with fast, high current load transients.
To keep cost and complexity low, the LT1573 uses a new
time-delayed latching overcurrent protection technique
that requires no external current sense resistor. Base drive
is limited for instantaneous protection, and a time-delayed
latch protects the regulator from continuous short
circuits.
The LT1573 is available as an adjustable regulator with an
output range of 1.27V to 6.8V and with fixed output
voltages of 2.5V, 2.8V and 3.3V. Output accuracy is better
than 1% to meet the critical regulation requirement of fast
microprocessors. A special 8-pin, fused-lead surface mount
package is used to minimize regulator footprint and pro-
vide adequate heat sinking.
APPLICATIO S
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3.3V to 2.5V Regulators
Microprocessor Power Sources
Post Regulator for Switching Supplies
High Efficiency Linear Regulators
Ultralow Dropout Regulators
Low Voltage Linear Regulators
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
C
C
100pF
FB
LATCH
COMP
V
OUT
V
IN
DRIVE
R
C
1k
+
C
TIME
GND
V
IN
5V
LT1573
SHDN
R
D
24Ω
R
B
50Ω
Q
OUT
MOTOROLA
D45H11
50mV/DIV
V
OUT
3.3V
LOAD
R2
1k
GND
1573 F01
C
IN
100µF
TANT
+
C
OUT1
1µF
CER
×
24
+
C
OUT2
220µF
TANT
R1
1.6k
2.5A/DIV
10µs/DIV
V
OUT
= 1.265V (1 + R1/R2)
FOR T < 45°C, C
OUT1
= 24
×
1µF Y5V CERAMIC SURFACE MOUNT CAPACITORS.
FOR T > 45°C, C
OUT1
= 24
×
1µF X7R CERAMIC SURFACE MOUNT CAPACITORS.
PLACE C
OUT1
IN THE MICROPROCESSOR SOCKET CAVITY
Figure 1. 3.3V, 5A Microprocessor Supply
U
Transient Response for
0.2A to 5A Output Load Step
1573 F01a
U
U
1
LINER [ LINEAR TECHNOLOGY ]
