1

LTC1772

Constant Frequency

Current Mode Step-Down

DC/DC Controller in SOT-23

September 1999

FEATURES

The LTC

down DC/DC controller providing excellent AC and DC load

and line regulation. The device incorporates an accurate

undervoltage lockout feature that shuts down the LTC1772

when the input voltage falls below 2.0V.

The LTC1772 boasts a

±2.5%outputvoltageaccuracyand

consumes only 270

µA of quiescent current. For applica-

tions where efficiency is a prime consideration, the LTC1772

is configured for Burst Mode operation, which enhances

efficiency at low output current.

To further maximize the life of a battery source, the

external P-channel MOSFET is turned on continuously in

dropout (100% duty cycle). In shutdown, the device draws

a mere 8

µA. High constant operating frequency of 550kHz

allows the use of a small external inductor.

The LTC1772 is available in a small footprint 6-lead

SOT-23.

Figure 1. High Efficiency Step-Down Converter

s

One or Two Lithium-Ion-Powered Applications

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Cellular Telephones

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Wireless Modems

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Portable Computers

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Distributed 3.3V, 2.5V or 1.8V Power Systems

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Scanners

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High Efficiency: Up to 94%

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High Output Currents Easily Achieved

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Constant Frequency 550kHz Operation

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Burst Mode

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Low Dropout: 100% Duty Cycle

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0.8V Reference Allows Low Output Voltages

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Current Mode Operation for Excellent Line and Load

Transient Response

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Low Quiescent Current: 270

µA

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Shutdown Mode Draws Only 8

µA Supply Current

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±2.5% Reference Accuracy

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Tiny 6-Lead SOT-23 Package

Efficiency vs Load Current

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

Burst Mode is a trademark of Linear Technology Corporation.

LTC1772

10k

R1

0.03

Ω

169k

78.7k

L1

4.7

µH

M1

D1

220pF

C1: TAIYO YUDEN CERAMIC EMK325BJ106MNT

C2: SANYO POSCAP 6TPA47M

D1: IR10BQ015

L1: MURATA LQN6C-4R7

M1: Si3443DV

R1: DALE 0.25W

GND

6

5

4

1772 F01a

1

2

3

PGATE

C1

10

µF

16V

2.5V

TO 9.8V

2.5V

2A

C2

47

µF

6V

+

LOAD CURRENT (mA)

60

80

100

50

70

90

1

100

1000

10000

1772 F01b

40

10

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