3

Typical application schematic

The following image is a simplified schematic for the typical application

VOSNS

CC1/2

GPIO0/1

PGND

LEB

P3V3

HS

OR

SR

LS

AC

AC

n:1

The IC requires some external components to operate. On the primary side a driver and two FETs are required to

operate the power transformer, plus a clamp capacitor which stores the residual energy in the leakage inductance

at low-side turn-off and recovers it at the end of each cycle. A circuit to provide power to the IC after the high

voltage startup is connected to an auxiliary winding of the transformer, while a scaled voltage from the auxiliary

winding is used to provide an overvoltage function.

On the secondary side a synchronous rectifier FET is connected to the SRGD pin, while a cascode FET is

connected to the SRVDS to provide synchronous rectifier drain voltage sense while limiting the voltage on the pin

below its AMR.

An N-channel MOSFET connected to ORGD pin is used as load switch to disconnect the output voltage as

required by USB-PD power supplies. A sense resistor is connected to CSM/CSP pins to read the output current.

A capacitor and two diodes are connected to the PUMP pin to implement a charge pump providing the driving

voltage to the synchronous rectifier.

ST-ONE

Typical application schematic

DB4752 - Rev 1

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