STSR3, STSR3CD, STSR3CD-TR

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STSR3
SYNCHRONOUS RECTIFIERS SMART DRIVER FOR FLYBACK
s s

s s s

s

SUPPLY VOLTAGE RANGE: 4V TO 5.5V TYPICAL PEAK OUTPUT CURRENT: (SOURCE 2A, SINK 3.5A) OPERATING FREQUENCY: 30 TO 750 KHz SMART TURN-OFF ANTICIPATION TIMING AUTOMATIC TURN OFF FOR DUTY CYCLE LESS THAN 14% POSSIBILITY TO OPERATE IN DISCONTINUOUS MODE

SO-8

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 From a synchronizing clock input, withdrawn on the secondary side of the isolation transformer, the IC generates a driving signal with set dead times with respect to the primary side PWM signal.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.

SCHEMATIC DIAGRAM
Vcc
2

+
BIAS UVLO

5.7V

CK 4

PEAK DETECTOR

ANTICIPATION SET

3 SETANT

+
HIGH FREQUENCY OSCILLATOR

DIGITAL CONTROL

OUTPUT BUFFER

+

7 OUTGATE

INHIBIT 5

+ 25mV

1 N/C

6

8

SGLGND

PWRGND

June 2003

1/12

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STSR3 DATASHEET