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June 2003

s

SUPPLY VOLTAGE RANGE: 4.5V TO 5.5V

s

TYPICAL PEAK OUTPUT CURRENT:

SOURCE -2A, SINK 3.5A

s

OPERATING FREQUENCY: 20 TO 750 KHZ

s

SMART TURN-OFF ANTICIPATION TIMING

s

OPERATION INDEPENDENT FROM THE

FORWARD MAGNETIC RESET TECHNIQUE

s

POSSIBILITY TO OPERATE IN

DISCONTINUOUS MODE

DESCRIPTION

STSR2

Smart

Driver

IC

provides

two

complementary high current outputs to drive

Power Mosfets. The IC is dedicated to properly

drive

secondary

Synchronous

Rectifiers

in

medium power, low output voltage, high efficiency

Forward Converters. From a synchronizing clock

input, STSR2 generates two driving signals with

the

self-setting

of

dead

time

between

complementary pulses. The IC operation prevents

secondary

side

shoot-through

conditions

providing proper timing at the outputs turn-off

transition. This smart function operates through a

fast cycle-after-cycle control logic mechanism

based on an internal high frequency oscillator,

synchronized

by

the

clock

signal.

A

fixed

respect to the clock signal transition is provided,

can be set through external components. The

adopted transitions revelation mechanism makes

circuit operation independent by the forward

magnetic reset technique used, avoiding most of

the common problems inherent in self-driven

synchronous rectifiers. A special Inhibit function

makes discontinuous conduction mode possible

and prevents the freewheeling mosfet from

sinking current from the output.

STSR2 automatically turns off the outputs when

duty-cycle is lower than 13%, while STSR2M

works even at very low duty-cycle values.

STSR2

FORWARD SYNCHRONOUS

RECTIFIERS SMART DRIVER

PEAK

DETECTOR

BIAS

UVLO

CK

Vcc

6

5.7V

8

4

2

OUTPUT

BUFFERS

7

OUTGate2

PWRGND

SGLGND

ANTICIPATION

SET

5

INHIBIT

25mV

-

+

DIGITAL

CONTROL

HIGH

FREQUENCY

OSCILLATOR

1

OUTGate1

+

+

+

SCHEMATIC DIAGRAM

SO-8