1

LTC1735-1

High Efficiency

Synchronous Step-Down

Switching Regulator

The LTC

regulator controller optimized for CPU power. OPTI-LOOP

compensation allows the transient response to be opti-

mized over a wide range of output capacitance and ESR

values.

The operating frequency (synchronizable up to 500kHz) is

set by an external capacitor allowing maximum flexibility

in optimizing efficiency. The output voltage is monitored

by a power good window comparator that indicates when

the output is within 7.5% of its programmed value, con-

forming to Intel Mobile CPU Specifications.

Protection features include internal foldback current lim-

iting, output overvoltage crowbar and optional short-

circuit shutdown. Soft-start is provided by an external

capacitor that can be used to properly sequence supplies.

The operating current level is user-programmable via an

external current sense resistor. Wide input supply range

allows operation from 3.5V to 30V (36V maximum).

Pin defeatable Burst Mode

efficiency at low load currents while 99% duty cycle

provides low dropout operation.

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Dual N-Channel MOSFET Synchronous Drive

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Programmable/Synchronizable Fixed Frequency

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s

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Very Low Dropout Operation: 99% Duty Cycle

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OPTI-LOOP

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Power Good Output Voltage Monitor

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Internal Current Foldback

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Output Overvoltage Crowbar Protection

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Latched Short-Circuit Shutdown Timer

with Defeat Option

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Optional Programmable Soft-Start

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Remote Output Voltage Sense

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Available in 16-Lead Narrow SSOP and SO Packages

Figure 1. CPU Core DC/DC Converter with Dynamic Voltage Selection from SpeedStep Enabled Processors

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

Burst Mode and OPTI-LOOP are trademarks of Linear Technology Corporation.

Pentium is a registered trademark of Intel Corporation. SpeedStep is a trademark of Intel

Corporation.

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Notebook and Palmtop Computers, PDAs

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Power Supply for Mobile Pentium

SpeedStep

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Cellular Telephones and Wireless Modems

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2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

RUN/SS

PGOOD

SGND

TG

BOOST

SW

BG

PGND

LTC1735-1

1000pF

47pF

+

4.7

µF

5V

(OPTIONAL)

47pF

Q4

2N7002

GND

47pF

R1

10k

0.5%

L1: PANASONIC ETQP6RZ1R20HFA

1.35V TO 1.60V

12A

D1

CMDSH-3

D2

MBRS340T3

Q1

FDS6680A

22

µF

50V

CERAMIC

×2

L1

1.2

µH

0.004

Ω

4.5V TO 24V

PGOOD

Q2, Q3

FDS6680A

×2

10

Ω

1735-1 F01

R3

33.2k

1%

R2

14.3k

0.5%

10

Ω

+

180

µF

4V

PANASONIC SP

×4

DESCRIPTIO

FEATURES

APPLICATIO S

TYPICAL APPLICATIO