1

LTC1267

LTC1267-ADJ/LTC1267-ADJ5

Dual High Efficiency

Synchronous Step-Down

Switching Regulators

Figure 1. High Efficiency Dual 3.3V, 5V

S

FEATURE

DESCRIPTIO

switching regulator controllers featuring automatic Burst

output currents. The LTC1267 is composed of two sepa-

rateregulatorblocks,eachdrivingapairofexternalcomple-

mentary power MOSFETs at switching frequencies up to

400kHz. The LTC1267 uses a constant off-time current-

mode architecture to provide constant ripple current in the

inductor and provide excellent line and load transient

response.

A separate pin and on-board switch allow the MOSFET

driver power to be derived from the regulated output

voltage,providingsignificantefficiencyimprovementwhen

operating at high input voltage. The output current level is

user-programmable via an external current sense resistor.

The LTC1267 series is ideal for applications requiring dual

output voltages with high conversion efficiencies over a

wide load current range in a small amount of board space.

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Dual Outputs: 3.3V and 5V, Two Adjustables or

Adjustable and 5V

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Ultra-High Efficiency: Up to 95%

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Low Supply Current in Shutdown: 20

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Current Mode Operation for Excellent Line and Load

Transient Response

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High Efficiency Maintained Over a Wide Output

Current Range

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Independent Micropower Shutdown

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Very Low Dropout Operation: 100% Duty Cycle

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Synchronous FET Switching for High Efficiency

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Available in Standard 28-Pin SSOP

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Notebook and Palmtop Computers

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Battery-Operated Digital Devices

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Portable Instruments

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DC Power Distribution Systems

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APPLICATI

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

Burst Mode is a trademark of Linear Technology Corporation.

APPLICATI

TYPICAL

1000pF

+

+

+

1000pF

PGATE 3

PDRIVE 3

SHDN3

PDRIVE 5

SHDN5

NGATE 3

SGND5 PGND5

NGATE 5

PGATE 5

CAP3

CAP5

MSHDN

LTC1267

270pF

7

11

9

10

15

16

20

22

1k

3300pF

3300pF

270pF

1k

1

2

3

0.15

µF

0.15

µF

8

1N4148

26

27

1

28

25

24

18

17

19

23

4

5

14

13

12

6

5V

2A

220

µF

10V

× 2

0.05

Ω

P-CH

Si9435DY

L5

33

µH

D5

MBRS140T3

N-CH

Si9410DY

100

µF

50V

+

3.3

µF

0.1

µF

0.1

µF

100

µF

50V

P-CH

Si9435DY

N-CH

Si9410DY

D3

MBRS140T3

220

µF

10V

× 2

L3

20

µH

0.05

Ω

3.3V

2A

5.4V to 25V

L3: COILTRONICS CTX20-4

L5: COILTRONICS CTX33-4

SHDN3, SHDN5, MSHDN

0V = NORMAL, >2V = SHDN

LTC1267 • F01

+

3.3

µF

+

1N4148

FOR INFORMATION PURPOSES ONLY

OBSOLETE:

Contact Linear Technology for Potential Replacement