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LTC1553

5-Bit Programmable

Synchronous Switching

Regulator Controller for

Pentium

FEATURES

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5-Bit Digitally Programmable 1.8V to 3.5V Fixed

Output Voltage

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Provides All Features Required by the

Intel

Pentium

Converter Specification

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Flags for Power Good, Over-Temperature and

Overvoltage Fault

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19A Output Current Capability from a 5V or 12V Supply

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Dual N-Channel MOSFET Synchronous Driver

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Initial Output Accuracy:

±1.5%

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Excellent Output Accuracy:

±2% Typ Over Line,

Load and Temperature Variations

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High Efficiency: Over 95% Possible

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Adjustable Current Limit Without External Sense

Resistors

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Fast Transient Response

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Available in 20-Lead SSOP and SW Packages

The LTC

regulator controller optimized for 5V or 12V input to 1.8V-

3.5V output applications. It features a digitally programmable

output voltage, a precision internal reference and an internal

feedback system that provides output accuracy of

±1.5% at

room temperature and typically

±2%over-temperature,load

current and line voltage shifts. The LTC1553 uses a synchro-

nous switching architecture with two external N-channel

output devices, providing high efficiency and eliminating the

need for a high power, high cost P-channel device. Addition-

ally, it senses the output current across the on-resistance of

the upper N-channel FET, providing an adjustable current

limit without an external low value sense resistor.

The LTC1553 free-runs at 300kHz and can be synchronized

to a faster external clock if desired. It includes all the inputs

and outputs required to implement a power supply conform-

ing to the

Intel Pentium

Converter Specification.

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Power Supply for Pentium II, SPARC, ALPHA and

PA-RISC Microprocessors

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High Power 5V or 12V to 1.8V-3.5V Regulators

Figure 1. 5V to 1.8V-3.5V Supply Application

PWRGD

FAULT

OT

VID0 TO VID4

OUTEN

COMP

SS

SGND

GND

SENSE

10

µF

Q1*

20

Ω

Q2*

0.1

µF

12V

5V

2

µH

18A

LTC1553

G1

G2

+

0.1

µF

1553 F01

0.01

µF

8.2k

5.6k

2.7k

5.6k

5.6k

0.1

µF

0.1

µF

10

µF

1200

µF

× 4

1.8V TO

3.5V

14A

330

µF

× 7

+

+

C1

150pF

+

5

PENTIUM

SYSTEM

*SILICONIX SUD50N03-10

**SANYO 10MV1200GX

PANASONIC 12TS-2R5SP

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

Pentium is a registered trademark of Intel Corporation.