ON Semiconductor : NCP4305 – MOSFET driver helps synchronous-rectification circuits operate more efficiently


NCP4305: high efficiency at full and light loads

The NCP4305 from ON Semiconductor is a high-performance driver for controlling a synchronous-rectification MOSFET in switch-mode power supplies.

Highly versatile, the NCP4305 may be used in various topologies, including discontinuous-current and continuous-current mode flyback converters, quasi-resonant flyback converters, and forward and half-bridge resonant LLC converters.

The combination of externally adjustable minimum off-time and on-time blanking periods helps to mitigate the ringing induced by the PCB layout and other parasitic elements. The device’s self-synchronisation feature ensures reliable and noise-free operation of the synchronous-rectification circuit.

The NCP4305 also makes use of a Kelvin connection between the driver and the MOSFET to achieve efficient operation at full load. Lightload detection also helps the device to optimise operation for efficiency at light loads.

The precise turn-off threshold, extremely low turn-off delay time and high sink-current capability of the driver allow the MOSFET to maximise its conduction time in synchronous-rectification mode for the highest power-supply efficiency.

The high accuracy of the NCP4305 driver, and its 5V gate clamp, mean that users of the NCP4305 can opt to use Gallium Nitride (GaN) FETs in their power-supply design.


  • True secondary zero-current detection
  • 12ns turn-off delay
  • Rugged Current Sense pin
  • 8A peak sink-current capability
  • 4A peak current source-drive capability
  • 35V maximum supply voltage
  • 1MHz maximum operating frequency


  • Power adapters
  • High power-density AC-DC power supplies
  • Switch-mode power supplies with high efficiency requirements


ST’s STW42N60M2-EP
ON Semi’s NCP1399