Datasheet

V
DS
I
SEC
V
DS
V
DS
V
DS
I
SEC
I
SEC
I
SEC
(t)
V
THOFF
TON Blanking
Light-Load Mode
GATE Output
(A), (V)
V10092
V
DS
V
DS
V
DS
V
DS
I
SEC
I
SEC
I
SEC
I
SEC
(t)
V
THOFF
TON Blanking
Light-Load Mode
GATE Output
(A), (V)
V10091
UCC24610
www.ti.com SLUSA87B –AUGUST 2010–REVISED SEPTEMBER 2010
Light-Load Operation
During normal operation, the synchronous rectifier conduction time is longer than the programmed minimum
on-time. If load current decreases enough that the SR conduction time becomes shorter than the programmed
minimum on-time, a light-load condition is detected. The light-load latch is set and the next GATE output pulse is
blanked, so only the body diode of the controlled MOSFET conducts. This comparison between SR conduction
time and minimum on time occurs every switching cycle, regardless of whether the GATE output pulse is enabled
or blanked. When load current increases enough that the body-diode conduction time becomes longer than the
programmed minimum on time, the light-load latch is cleared and the next GATE output pulse is enabled and the
controlled MOSFET resumes SR operation.
Figure 20 depicts the progression into Light-Load Mode for a DCM flyback application as the load decreases,
while Figure 21 depicts the reverse progression back to Run Mode.
Figure 20. Decreasing Load Current Progression Leads to Light-Load-Mode Operation
Figure 21. Increasing Load Current Progression Returns to Run-Mode Operation.
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