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JW7707C Rev.0.8 JoulWatt Proprietary Information. Patent Protected. 1
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DEscriptION
JW7707C is a synchronous rectifier for Flyback
converters. It integrates a 60V power MOSFET
that can replace Schottky diode for high efficiency.
It turns on the internal MOSFET if the
VSW<-500mV and turns it off before the current
from GND to SW is lower than zero.
Company’s Logo is Protected, “JW” and “JOULWATT” are Registered
Trademarks of JoulWatt technology Inc.
FEATURES
Supports DCM and Quasi-Resonant Flyback
converter
Integrated 13m5 60V Power MOSFET
Supports High-side and Low-side
Rectification
No need external power supply
APPLICATIONS
Flyback converters
Adaptors
Operation
JW7707C is a synchronous rectifier, it can
replace the Schottky to improve the efficiency in
Flyback converters. It supports operation in
DCM and Quasi-Resonant Flyback converters.
It can power itself through the internal LDO
during the turn-off period, a 0.1uF capacitor is
needed between VCC and GND.
Turn-on Blanking Time
The control circuitry contains a blanking function.
When the internal MOSFET is turned on, it at
least last for some time, the turn on blanking
time is about 1uS. During the turn on blanking
period, the turn off threshold is not totally
blanked, but changes the threshold current.
This assures that the internal MOSFET can
always be turned off even during the blanking
period.
Under-Voltage Lockout (UVLO)
When the VCC is below UVLO threshold, the
internal MOSFET is turned off and never turned
on before the VCC exceeds the startup voltage.
Turn On Phase
The switch current first flows through the body
diode of integrate MOSFET, which generates a
negative VSW. When the VSW is higher than 0.7V
and then VSW is lower than VMOS_ON, it turns on
the integrate MOSFET after 24ns delay.
Turn Off Phase
The JW7707C senses the current of the internal
MOSFET ISW, before ISW is lower than Internal
MOS turn off threshold, the driver voltage of the
switch is pulled down to zero after 10ns delay.
Turn on and turn off delay
Startup
During the startup period, when the VCC is
lower than startup voltage, the internal MOSFET
is turned off. The current flows though body
diode until the VCC exceeds the startup voltage.
RC Snubber Circuit
In some applications (output short circuit
protection), the inductor current may go into
slight CCM condition. To avoid the voltage spike
across the synchronous rectifier, we suggest
RC snubber should be placed between SW and
GND, and a resistor should be paralleled with
VCC capacitor.