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

The LTC

switching regulator controllers featuring automatic Burst

Mode

output currents. The LTC1267 is composed of two sepa-

rate regulator blocks, each driving a pair of external comple-

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, providing significant efficiency improvement when

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.

s

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

Adjustable and 5V

s

s

Ultra-High Efficiency: Up to 95%

s

Low Supply Current in Shutdown: 20

s

Current Mode Operation for Excellent Line and Load

Transient Response

s

High Efficiency Maintained Over a Wide Output

Current Range

s

Independent Micropower Shutdown

s

Very Low Dropout Operation: 100% Duty Cycle

s

Synchronous FET Switching for High Efficiency

s

Available in Standard 28-Pin SSOP

s

Notebook and Palmtop Computers

s

Battery-Operated Digital Devices

s

Portable Instruments

s

DC Power Distribution Systems

S

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

3

0.15

µF

0.15

µF

8

1N4148

26

27

221

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