LTC1698IGN datasheet(8/24 Pages) LINER

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LTC1698

1698f

BLOCK DIAGRA

I-TO-V CONVERTER

RMARGIN

20k

ROVP

100k

VFB

0.94VREF

MPWRGD

RILIM

MILIM

MARGIN

SYNC

OPTODRV

±5% VREF

VREF

BANDGAP

SYNC IN

VCC

VDD

VAUX

–

ERR

–

ILIM

25mV

–

OVP

VREF

1698 BD

OPTO

PWRGD

OVPIN

ICOMP

ISNS

ISNSGND

VCOMP

VFB

PWRGD

AUX GEN

VCC GEN

OPERATIO

The LTC1698 is a secondary-side synchronous rectifier

controller designed to work with the LT3781 primary-side

synchronous controller chip to form an isolated synchro-

nous forward converter. This chip set uses a dual transis-

tor forward topology that is predominantly used in distrib-

uted power supply systems where isolated low voltages

are needed to power complex electronic equipment. The

primary stage is a current mode, fixed frequency forward

converter and provides the typical PWM operation. A

power transformer is used to provide the functions of

input/output isolation and voltage step-down to achieve

the required low output voltage. Instead of using typical

Schottky diodes, synchronous rectification on the sec-

ondary offers isolation with high efficiency. It supplies

high power without the need of bulky heat sinks, which is

often a problem in any space constrained application.

The LTC1698 not only provides synchronous drivers for

the external MOSFETs, it comes with other housekeeping

functions performed on the secondary side of the power

supply, all within a single integrated controller. Figure 1

shows the typical chip-set application. Upon power up, the

LTC1698’s VDD input is low, the gate drivers TG and BG are

both at the ground potential. The secondary forward and

(Refer to Block Diagram)

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