1

LT3781

3781f

FEATURES

APPLICATIO S

DESCRIPTIO

TYPICAL APPLICATIO

13

2

1

5

1

µF

150pF

OVLO

SHDN

73.2k

1%

20k

10k

270k

0.25W

68

µF

20V

6

FSET

4.7nF

8

SS

10

14

BAT54

ZVN3310F

9

PGND

37

4

THERM

LT3781

SYNC SGND

52.3k

100

Ω

1k

1%

100

Ω

2k

FZT690

4.7

µF

16V

0.22

µF

50V

CMPZ5242B

12V

3.3k

6.8k

10k

0.01

µF

12

SG

+

0.1

µF

11

SENSE

15

BG

18

BSTREF

19

TG

20

BAS21

0.1

µF

100V

C4

1.5

µF

100V

C3

1.5

µF

100V

L1

4.7

µH

R9

0.025

Ω

1/2W

Q3

1nF

100V

1nF

100V

Q5

Q6

MURS120T3

MURS120T3

Q1

T1

+

–

C2

22

µF

100V

+

–

C5

330

µF

10V

10

Ω

0.25W

10

Ω

0.25W

L2

4.7

µH

330pF

+

1.24k

1%

IN2

IN1

GND2

OUT2

OUT1

GND1

8

3

1

4

6

5

7

2

LTC1693-2

1OV

BIAS

1OV

BIAS

MBR-

0540T1

MMBD914LT1

5V

OUT

3.01k

1%

51

Ω

0.047

µF

6

7

5

8

4

9

1

2

3

10

11

12

1nF

4.7

Ω

+

C2:SANYO 100MV22AX

C3, C4: VITRAMON VJ1825Y155MXB

C5: 4X KEMET T510X337KO10AS

L1: COILCRAFT DO1608C-472

L2: PANASONIC ETQP6F4R1LF4

Q1,Q3:100V SILICONIX SUD40N10-25

Q5,Q6: SILICONIX Si4450

T1:COILTRONICS VP5-1200

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

s

High Voltage Operation up to 72V

s

Synchronizable Operating Frequency and Output

Switch Phase for Multiple Controller Systems

s

Synchronous Switch Output

s

Undervoltage Lockout Protection with 6V Hysteresis

for Self-Biased Power

s

Fixed Frequency Operation to 350kHz

s

Local

±1% Voltage Reference

s

Input Overvoltage Protection

s

Low Start-Up Current

s

Programmable Start Inhibit for Power Supply

Sequencing and Protection

s

Optocoupler Support

s

Soft-Start Control

“Bootstrap” Start Dual

Transistor Synchronous Forward Controller

36V-72V to 5V/7A DC/DC

Synchronous Forward Converter (Quarter-Brick Footprint)

s

Isolated Telecommunication Systems

s

Personal Computers and Peripherals

s

Distributed Power Step-Down Converters

s

Lead Acid Battery Backup Systems

s

Automotive and Heavy Equipment

The LT

power synchronous dual transistor forward DC/DC con-

verters. The part employs fixed frequency current mode

control and supports both isolated and nonisolated to-

pologies. The IC drives external N-channel power MOSFETs

and operates with input voltages up to 72V.

The LT3781 is ideal for output derived power schemes,

through the use of a large undervoltage lockout hysteresis

regulator, which prevents exceeding absolute maximum

ratings while in trickle start applications.

The LT3781’s operating frequency is programmable and

can be synchronized up to 350kHz. Switch phase is also

controlled during synchronized operation to accommo-

date multiple-converter systems. Internal logic guaran-

tees 50% maximum duty cycle operation to prevent trans-

former saturation.

The LT3781 is available in a 20-lead SSOP package.