APR348

Document number: DS42016 Rev. 5 - 2

5 of 9

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March 2021

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APR348

Synchronous Rectification Principle Description

Synchronous Rectification MOSFET Turn-On

The APR348 determines the synchronous rectification MOSFET turn-on time by monitoring the MOSFET drain-to-source voltage. Because of the

parasitic parameter, the voltage on the MOSFET drain pin has moderate voltage ringing, which may affect the SR controller VDET voltage sense

and bring about a turn-on/off fault.

To avoid this conduction fault, the APR348 has internal judge methods to determinate the turn-on moment of synchronous rectification MOSFET.

Meanwhile, APR348 has a minimum on-time (tON_MIN, which is shown in Figure 1) blanking period that keeps the power MOSFET on for a minimum

amount of time. When the controlled MOSFET gate turns on, some ringing noises generate. The minimum on-time timer blanks the VTHOFF

comparator, which keeps the controlled MOSFET on for at least the minimum on-time. During the minimum on-time, the turn-off threshold is blanked

unless the VDS ringing voltage goes over 2V during this period.

VDET

t

t

VDRISR

VFWD

VTHON

2V

Forward Regulation

Period

tDON

tON_MIN

0

0

Figure 1. APR348 Switch Period