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LTC1707

High Efficiency Monolithic

Synchronous Step-Down

Switching Regulator

December 1999

Final Electrical Specifications

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-

tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

Figure 1b. Efficiency vs Output Load Current

22

µF

16V

47pF

3V TO

8.5V

1707 F01a

6

2

7

1

5

8

3

SW

RUN

SYNC/MODE

LTC1707

+

15

µH

100

µF

6.3V

80.6k

3V < VIN < 3.3V

249k

3.3V

+

GND

4

OUTPUT CURRENT (mA)

1

70

90

95

100

10

100

1000

1707 F01b

85

80

75

Figure 1a. High Efficiency Low Dropout Step-Down Converter

The LTC

mode synchronous buck regulator using a fixed frequency

architecture. The operating supply range is from 8.5V

down to 2.85V, making it suitable for both single and dual

lithium-ion battery-powered applications. Burst Mode op-

eration provides high efficiency at low load currents.

100% duty cycle provides low dropout operation, extend-

ing operating time in battery-powered systems.

The switching frequency is internally set at 350kHz,

allowing the use of small surface mount inductors. For

noise sensitive applications it can be externally synchro-

nized up to 550kHz. Burst Mode operation is inhibited

during synchronization or when the SYNC/MODE pin is

pulled low preventing low frequency ripple from interfer-

ing with audio circuitry. Soft-start is provided by an

external capacitor.

The internal synchronous MOSFET switch increases effi-

ciency and eliminates the need for an external Schottky

diode, saving components and board space. Low output

voltages down to 0.8V are easily achieved due to the 0.8V

internal reference. The LTC1707 comes in an 8-lead SO

package.

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High Efficiency: Up to 96%

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Constant Frequency: 350kHz Synchronizable

to 550kHz

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0.8V Feedback Reference Allows Low Voltage

Outputs: 0.8V

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No Schottky Diode Required

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1.19V

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Selectable Burst Mode

Skipping Mode

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Low Dropout Operation: 100% Duty Cycle

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Precision 2.7V Undervoltage Lockout

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Current Mode Control for Excellent Line and

Load Transient Response

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Low Quiescent Current: 200

µA

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Shutdown Mode Draws Only 15

µA Supply Current

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Available in 8-Lead SO Package

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

Burst Mode is a trademark of Linear Technology Corporation.

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Cellular Telephones

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Portable Instruments

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Wireless Modems

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RF Communications

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Distributed Power Systems

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Single and Dual Cell Lithium

FEATURES

DESCRIPTIO

APPLICATIO S

TYPICAL APPLICATIO