LTC3705

1

3705fb

FEATURES

DESCRIPTIO

APPLICATIO S

TYPICAL APPLICATIO

2-Switch Forward Converter

Eliminate Need for Separate Gate Drive Bias

Supply

■

Linear Regulator Controller for Fast Start-Up

■

Volt-Second Limit Prevents Transformer Core

Saturation

■

Available in 16-Lead Narrow SSOP Package

2-Switch Forward

Controller and Gate Driver

The LTC

converter and includes on-chip bottom and top gate

drivers that do not require external transformers.

For secondary-side control, combine the LTC3705 with

the LTC3706 PolyPhase

forward controller to create a complete forward converter

using a minimum of discrete parts. A proprietary scheme

is used to multiplex gate drive signals across the isolation

barrier through a tiny pulse transformer. The on-chip

rectifier and the same pulse transformer provide gate drive

bias power.

Alternatively, the LTC3705 can be used as a standalone

voltage mode controller in a primary-side control architec-

ture with optoisolator feedback. Voltage feedforward pro-

vides excellent line regulation and transient response.

NDRV

GND

PGND VSLMT

UVLO

BOOST

LTC3705

BAS21

FQT7N10

0.22

µF

10

µF

CMPSH1-4

1.2

Ω

L1

1.2

µH

TG TS BG IS

T2

1

µF

162k

L1: COILCRAFT SER2010-122

T1: PULSE PA0807

T2: PULSE PA0297

33nF

30m

Ω

1W

2m

Ω

2W

Si7336ADP

Si7336ADP

×2

T1

•

•

MURS120

Si7852DP

Si7852DP

MURS120

33nF

15k

365k

100k

2.2

µF

SS/FLT

–

+

330

µF

6.3V

×3

2.2

µF

680pF

CZT3019

22.6k

20k

102k

–

3705 TA01

+

•

•

1

µF

100V

x3

FG

SW SG

NDRV

GND PGND PHASE SLP MODE REGSD

+

–

RUN/SS

LTC3706

ITH

FB

FS/SYNC

36V –72V to 3.3V/20A Isolated 2-Switch Forward Converter

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

PolyPhase is a registered trademark of Linear Technology Corporation. All other

trademarks are the property of their respective owners. Patent Pending