Datasheet APR348 (Diodes) - 5

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. When the drain voltage is lower than the turn-on threshold voltage (2V), the IC begins to prepare turn-on. Because of the parasitic parameter, the voltage on the MOSFET drain pin has moderate voltage ringing, which may impact the SR controller VDET voltage sense and bring about a turn-on/off fault. To avoid this fault situation happening, the APR348 has several judge criteria to determinate whether synchronous rectification MOSFET turns on properly including:
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a) A programmable VDET slew rate detection to determine turn-on time
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b) A minimum on-time (tONMIN) blanking period that keeps the power MOSFET on for a minimum amount of time
U D O
Figure 1 shows the turn-on blanking time tONMIN, which prevents the MOSFET drain-to-source voltage from ringing effect. When the controlled
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MOSFET gate turns on, some ringing noise is generated. 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 V
P
DS ringing voltage goes over 2V during this period.
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VDET 2V 0 VFWD t VTHON VDRISR 0 tDON t Forward Regulation Period tON_MIN
Figure 1. APR348 Switch Period
APR348 5 of 9 December 2019 Document number: DS42016 Rev. 3 - 2
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