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April 2003

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GLITCH FREE TRANSITION BETWEEN

INPUT SOURCES

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INTERNAL LOGIC SELECTS INPUT

SOURCE

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GATE DRIVE FOR EXTERNAL PMOS

BYPASS SWITCH

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5V DETECTOR WITH HYSTERESIS

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1% 3.3V REGULATED OUTPUT VOLTAGE

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500mA GUARANTEED OUTPUT CURRENT

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OPERATING TEMPERATURE RANGE

FROM 0°C TO 85°C

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PPAK AND SO-8 PACKAGES CAN BE

AVAILABLE ON REQUEST

APPLICATIONS

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NETWORK INTERFACE CARDS

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PCMCIA/PCI INTERFACE CARDS

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DESKTOP COMPUTERS

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POWER SUPPLY WITH MULTIPLE INPUT

SOURCES

DESCRIPTION

The ST1534A is intended for application such as

power managed PCI and network interface cards

(NICs), where operations from 3.3V VAUX supply

may be required when the 5V supply has been

shut down.

During regular operation, 3.3V power for the PCI

card is provided by the internal LDO regulator,

available, the IC connects this supply directly to its

output using an external P-Channel FET. This

ensures an uninterrupted 3.3V out even if VIN falls

out of specification.

When both supplies are available simultaneously,

the drive pin DR will be pulled high, turning off the

PMOS switch.

The device is available in the popular 5 leads

ST1534A

500mA SMART LDO

-

+

-

+

DR

Reference

Error

Amp

5V Detect

Rpull_down

GND

SCHEMATIC DIAGRAM

SO-8

PPAK