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June 2003

s

SUPPLY VOLTAGE RANGE: 4V TO 5.5V

s

TYPICAL PEAK OUTPUT CURRENT:

(SOURCE 2A, SINK 3.5A)

s

OPERATING FREQUENCY: 30 TO 750 KHz

s

SMART TURN-OFF ANTICIPATION TIMING

s

AUTOMATIC TURN OFF FOR DUTY CYCLE

LESS THAN 14%

s

POSSIBILITY TO OPERATE IN

DISCONTINUOUS MODE

DESCRIPTION

STSR3 Smart Driver IC provides a high current

outputs

to

properly

drive

secondary

Power

Mosfets used as Synchronous Rectifier in low

output

voltage,

high

efficiency

Flyback

Converters. From a synchronizing clock input,

withdrawn on the secondary side of the isolation

transformer, the IC generates a driving signal with

set dead times with respect to the primary side

PWM signal.

The

IC

operation

prevents

secondary

side

shoot-through conditions at turn-on of the primary

switch providing anticipation in turn-off the output.

This smart function is implemented by a fast

cycle-after-cycle logic control mechanism, based

on a high frequency oscillator synchronized by the

clock signal. This anticipation is externally set

through external component. A special Inhibit

function allows to shut-off the drive output. This

feature makes discontinuous conduction mode

possible and avoids reverse conduction of the

synchronous rectifier.

STSR3

SYNCHRONOUS RECTIFIERS

SMART DRIVER FOR FLYBACK

PEAK

DETECTOR

BIAS

UVLO

CK

Vcc

6

5.7V

8

4

2

OUTPUT

BUFFER

1

N/C

PWRGND

SGLGND

ANTICIPATION

SET

3

5

INHIBIT

25mV

-

+

DIGITAL

CONTROL

HIGH

FREQUENCY

OSCILLATOR

7

+

+

+

SETANT

SCHEMATIC DIAGRAM

SO-8