lt3781 Linear Technology Corporation, lt3781 Datasheet

lt3781

Manufacturer Part Number

lt3781

Description

Bootstrap Start Dual Transistor Synchronous Forward Controller

Manufacturer

Linear Technology Corporation

Datasheet

1.LT3781.pdf (20 pages)

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FEATURES

APPLICATIO S

TYPICAL APPLICATIO

68 F

20V

–

0.1 F

High Voltage Operation up to 72V

Synchronizable Operating Frequency and Output

Switch Phase for Multiple Controller Systems

Synchronous Switch Output

Undervoltage Lockout Protection with 6V Hysteresis

for Self-Biased Power

Fixed Frequency Operation to 350kHz

Local 1% Voltage Reference

Input Overvoltage Protection

Low Start-Up Current

Programmable Start Inhibit for Power Supply

Sequencing and Protection

Optocoupler Support

Soft-Start Control

Isolated Telecommunication Systems

Personal Computers and Peripherals

Distributed Power Step-Down Converters

Lead Acid Battery Backup Systems

Automotive and Heavy Equipment

0.25W

270k

1nF

10k

73.2k

20k

4.7 H

22 F

100V

BIAS

1.24k

1OV

MMBD914LT1

1.5 F

100V

BAS21

OVLO

SHDN

1 F

BST

1.5 F

100V

REF

52.3k

0.1 F

100V

Transistor Synchronous Forward Controller

FSET

150pF

Synchronous Forward Converter (Quarter-Brick Footprint)

BSTREF

THERM

LT3781

SYNC SGND

SENSE

4.7nF

ZVN3310F

MURS120T3

PGND

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

100

BAT54

10k

330pF

0.01 F

MURS120T3

OUT

0.047 F

3.01k

0.025

1/2W

DESCRIPTIO

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

range. The part is also equipped with an 18V V

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.

3.3k

6.8k

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

3781 controller simplifies the design of high

IN2

IN1

GND2

LTC1693-2

CC1

“Bootstrap” Start Dual

BIAS

1OV

GND1

OUT2

OUT1

CC2

C2:SANYO 100MV22AX

C3, C4: VITRAMON VJ1825Y155MXB

C5: 4X KEMET T510X337KO10AS

L1: COILCRAFT DO1608C-472

4.7 F

100V

FZT690

1nF

16V

100V

0.25W

1nF

CMPZ5242B

100

12V

0.22 F

50V

4.7 H

4.7

L2: PANASONIC ETQP6F4R1LF4

Q1,Q3:100V SILICONIX SUD40N10-25

Q5,Q6: SILICONIX Si4450

T1:COILTRONICS VP5-1200

MBR-

0540T1

LT3781

330 F

10V

OUT

shunt

= 7A

= 5V

–

3781f

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