1

LT1573

Low Dropout

PNP Regulator Driver

Figure 1. 3.3V, 5A Microprocessor Supply

s

Low Cost Solution for High Current, Low Dropout

Regulators

s

Fast Transient Response Needs Much Less

Bulk Capacitance

s

Latching Overload Protection Minimizes

Heat Sink Size

s

Precision Output Voltage (1%)

s

s

Small Surface Mount Package

s

Capable of Very Low Dropout Voltage (<0.2V)

s

Fixed or Adjustable Outputs

s

Shutdown

s

3.3V to 2.5V Regulators

s

Microprocessor Power Sources

s

Post Regulator for Switching Supplies

s

High Efficiency Linear Regulators

s

Ultralow Dropout Regulators

s

Low Voltage Linear Regulators

The LT

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.

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

COMP

DRIVE

FB

LATCH

SHDN

GND

LT1573

+

220

µF

TANT

1

µF

CER

× 24

100pF

5V

1k

24

Ω

3.3V

GND

1573 F01

50

Ω

R1

1.6k

R2

1k

LOAD

+

+

MOTOROLA

D45H11

FOR T < 45

FOR T > 45

100

µF

TANT

Transient Response for

0.2A to 5A Output Load Step

10

µs/DIV

1573 F01a

50mV/DIV

2.5A/DIV

FEATURES

DESCRIPTIO

APPLICATIO S

TYPICAL APPLICATIO