ZXGD3105N8_15 Datasheet, PDF (10/14 Pages) Diodes Incorporated – SYNCHRONOUS MOSFET CONTROLLER IN SO-8

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ZXGD3105N8
Application Information (cont.)
Besides that, Proportional Gate Drive improves the rectifier efficiency even at light to medium load condition by ensuring that the MOSFETs
conduct during majority of the conduction cycle as shown in Figure 5a.
At reduced load condition, early termination of the gate drive voltage is likely for digital level gate drive due to the low current, which means that
the threshold V_T is breached. With the early termination of the gate drive voltage, MOSFET turns off and the body diode conducts, see Figure 5.
This is shown by an increase in Drain-GND voltage for the remaining time of the current waveform. With the current flowing through the body
diode there will be an increase in power developed within the MOSFET. The efficiency impact due to early termination of digital level gate driver
increases with lower R_DS(on) MOSFET and/or higher operating frequency.
(a)
(b)
Figure 5 Timing diagram of synchronous rectification in the resonant converter
(a) Proportional Gate Drive and (b) Digital Level Gate Drive
ZXGD3105N8
Document Number DS35101 Rev. 3 - 2
10 of 14
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March 2013
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