启达启臣微CR3011High Performance Synchronous Rectifier
CR3011FEATURES
Synchronous Rectification for isolated
Flyback
Synchronous Rectification for CCM、
CR3011DCM and QR mode
Operating frequency up to 400kHz
VDD UVLO protection
VDD voltage clamp
Low Standby Power to meet DOE Lot
CR30116 requirement
Simplify system design
SOT23-5L green Packaging
CR3011APPLICATIONS
Switching AC/DC Small Power Adaptor
Cell Phone Charger
Low voltage rectification circuits
CR3011GENERAL DESCRIPTION
CR3011 is a high performance Synchronous Rectifier controller for isolated flyback
Synchronous Rectifier applications. CR3011 is designed to be suitable for converters working in
discontinuous conduction mode (DCM)、continuous conduction mode (CCM) and quasi-resonant
mode (QRM). A low voltage drop N-channel MOSFET is controlled by CR3011 to emulate the
traditional diode rectifier at the secondary side of flyback converter, which can improve the power
delivery efficiency and reduce heat dissipation effectively. Its high integration allows the design of
a cost-effective power supply with a very low number of external components. The chip regulates
the forward drop of an external switch to about 70mV and switches it off as soon as the voltage
becomes negative. CR3011 is offered in SOT23-5L package.
CR3011OPERATION DESCRIPTION
CR3011 is a high performance Synchronous Rectifier controller for isolated flyback
Synchronous Rectifier applications. CR3011 is designed to be suitable for converters working in
discontinuous conduction mode (DCM)、continuous conduction mode (CCM) and quasi-resonant
mode (QRM). A low voltage drop N-channel MOSFET is controlled by CR3011 to emulate the
traditional diode rectifier at the secondary side of flyback converter, which can improve the power
delivery efficiency and reduce heat dissipation effectively.
CR3011Under-Voltage Lockout (UVLO)
When VDD is below UVLO_ OFF threshold, the GATE output is pulled low by an internal
resistor and never turned on before the VDD exceeds the startup voltage. When VDD rises above
UVLO_ OFF , the IC wakes up from under voltage lock out state and enter normal operation. When
VDD drops below UVLO_ ON , the IC enters under voltage lock out state again. In addition, there is
a hysteresis window(1.2V) between UVLO_ OFF which make system work reliably.
CR3011Synchronous Rectification Control
As shown in figure 1, when the synchronous MOSFET is conducting, current will flow
through its body diode which generates a negative V DS across it. Because this body diode voltage
drop (<-500mV) is much smaller than the turn on threshold of the control circuitry (-70mV),
which will then pull the gate driver voltage high to turn on the synchronous MOSFET after about
150ns turn on delay.
