1

LTC1877

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High Efficiency: Up to 95%

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Very Low Quiescent Current: Only 10

During Operation

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2.65V to 10V Input Voltage Range

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550kHz Constant Frequency Operation

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Synchronizable from 400kHz to 700kHz

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Selectable Burst Mode

Pulse Skipping Mode

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No Schottky Diode Required

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Low Dropout Operation: 100% Duty Cycle

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0.8V Reference Allows Low Output Voltages

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Shutdown Mode Draws < 1

µA Supply Current

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±2% Output Voltage Accuracy

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Current Mode Control for Excellent Line and

Load Transient Response

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Overcurrent and Overtemperature Protected

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Available in 8-Lead MSOP Package

The LTC

nous buck regulator using a constant frequency, current

mode architecture. Supply current during operation is

only 10

µA and drops to < 1µA in shutdown. The 2.65V to

10V input voltage range makes the LTC1877 ideally suited

for both single and dual Li-Ion battery-powered applica-

tions. 100% duty cycle provides low dropout operation,

extending battery life in portable systems.

Switching frequency is internally set at 550kHz, allowing

the use of small surface mount inductors and capacitors.

For noise sensitive applications the LTC1877 can be

externally synchronized from 400kHz to 700kHz. Burst

Mode operation is inhibited during synchronization or

when the SYNC/MODE pin is pulled low, preventing low

frequency ripple from interfering with audio circuitry.

The internal synchronous switch increases efficiency and

eliminates the need for an external Schottky diode. Low

output voltages are easily supported with the 0.8V feed-

back reference voltage. The LTC1877 is available in a

space saving 8-lead MSOP package. Lower input voltage

applications (less than 7V abs max) should refer to the

LTC1878 data sheet.

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Cellular Telephones

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Wireless Modems

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Personal Information Appliances

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Portable Instruments

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Distributed Power Systems

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Battery-Powered Equipment

High Efficiency Step-Down Converter

High Efficiency

Monolithic Synchronous

Step-Down Regulator

May 2000

FEATURES

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

Burst Mode is a trademark of Linear Technology Corporation.

Efficiency vs Output Current

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.

Final Electrical Specifications

OUTPUT CURRENT (mA)

0.1

10

1000

100

95

90

85

80

75

70

65

60

55

50

1877 • TA02

1.0

100

L = 10

µH

Burst Mode OPERATION

47

µF***

7

6

1

2

5

3

4

SW

LTC1877

GND

10

µH*

10

µF**

CER

220pF

VOUT

†

3.3V

887k

280k

1877 TA01

SYNC

RUN

2.65V

TO 10V

20pF

+