1. General description
The NEX81801DA and NEX81802DA
(NEX81801/2DA) are high performance synchronous
rectification controllers used in switching mode power
supplies. It supports operation in Discontinuous
Conduction Mode (DCM), Continuous Conduction
Mode (CCM) and quasi-resonant flyback converters.
The NEX81801/2DA regulates the forward drop
voltage of an external synchronous rectifier (SR)
MOSFET in two stages. This allows the SR FET to turn
off quickly when the VDS becomes positive.
The externally adjustable turn-on blanking time can
effectively prevent the synchronous rectifier from
being falsely turned off due to leakage inductance and
parasitic parameter oscillation.
The adaptive turn-on detection circuit can prevent
the SR from being mistakenly turned on when the
VDS DCM oscillation crosses zero during some load
conditions. The adaptive turn-on detection circuit also
enhances SR conduction efficiency during light load
conditions, thereby improving the average efficiency of
the power supply across the entire load range.
The synchronous switch can be configured at high-side
or low-side output without auxiliary windings or other
power sources, because the NEX81801/2DA has a
self-supply capability.
The NEX81801/2DA uses TSOT23-6 packaging with
low thermal resistance. This can effectively reduce the
junction temperature of the chip, making it suitable for
high-density power supply design.

2. Features and benefits
• Supports DCM, CCM, QR operation
• Supports up to 800 kHz switching frequency
• Standard and logic level MOSFET driving capability
• Wide output range down to 0 V with 2-channel VCC
supply
• No need for auxiliary winding for high-side or lowside
rectification
• Smart proportional gate driver for fast SR turn-off at
CCM
• Adjustable turn-on blanking time for increased
noise immunity
• Proprietary adaptive turn-on detection prevents SR
FET from falsely turning on during DCM operation
• 10 ns typical turn-off propagation delay
• Available in a TSOT23-6 FC package
• ESD protection:
• HBM: ANSI/ESDA/JEDEC JS-001 class 2
exceeds 2000 V
• CDM: ANSI/ESDA/JEDEC JS-002 class C2a
exceeds 500 V

3. Applications
• USB PD/QC chargers
• AC/DC adapters for portable devices
• Flyback SMPS with high-efficiency requirements