1

LTC1772B

FEATURES

APPLICATIO S

DESCRIPTIO

Constant Frequency

Current Mode Step-Down

DC/DC Controller in SOT-23

The LTC

step-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

LTC1772B when the input voltage falls below 2.0V.

The LTC1772B provides a

±2.5% output voltage accuracy

and consumes only 270

µA of quiescent current. In shut-

down, the device draws a mere 8

µA.

To further maximize the life of a battery source, the

external P-channel MOSFET is turned on continuously in

dropout (100% duty cycle). High constant operating

frequency of 550kHz allows the use of a small external

inductor.

The LTC1772B is available in a small footprint 6-lead

SOT-23.

For a Burst Mode operation enabled version of the

LTC1772B, please refer to the LTC1772 data sheet.

Figure 1. High Efficiency, High Output Current 2.5V/2A Regulator

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One or Two Lithium-Ion-Powered Applications

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Cellular Telephones

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Wireless Devices

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Portable Computers

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Distributed 3.3V, 2.5V or 1.8V Power Systems

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Burst Mode

Ripple at Light Loads

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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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Low Dropout: 100% Duty Cycle

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Output Voltage down to 0.8V

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Current Mode Operation for Excellent Line and Load

Transient Response

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Shutdown Mode Draws Only 8

µA Supply Current

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Tiny 6-Lead SOT-23 Package

Efficiency vs Load Current*

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

LTC1772B

10k

R1

0.03

Ω

174k

80.6k

L1

4.7

µH

M1

D1

220pF

C1: TAIYO YUDEN LMK325BJ106K-T

C2A: SANYO 6TPA47M

C2B: AVX 0805ZC105KAT1A

D1: MOTOROLA MBRM120T3

L1: MURATA LQN6C-4R7

M1: FAIRCHILD FDC638P

R1: IRC LRC-LR1206-01-R030F

GND

6

5

4

1772 F01a

1

2

3

PGATE

C1

10

µF

10V

C2B

1

µF

10V

2.5V

TO 9.8V

2.5V

2A

C2A

47

µF

6V

+

Burst Mode is a trademark of Linear Technology Corporation.

LOAD CURRENT (mA)

80

85

100

70

75

65

60

90

95

100

1000

10000

10

LTC1772

BURST MODE

OPERATION

LTC1772B

NON-BURST MODE

OPERATION

*OUTPUT RIPPLE WAVEFORMS FOR THE CIRCUIT

OF FIGURE 1 APPEAR IN FIGURE 2.

1772 F01b