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ISD

VDS

SR ON

TOFFBLANK

Clamp

Abs. Min

TRing

2.2TRing

20

UCC24612

SLUSCM5A – AUGUST 2017 – REVISED FEBRUARY 2018

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Feature Description (continued)

Figure 21. Adaptive Off-Time Blanking with DCM Ring Clamp

For some conditions, as mentioned earlier, the off blanking timer suitable for DCM operation might be too long

for high-line QR operation. In this case, the off blanking timer clamp needs to be reset to the correct value.

UCC24612 continuously monitors the SR body diode conduction time during minimum off-time. If the body diode

conduction time is longer than the minimum on-time, this means the minimum off blanking time clamp setting is

too long and needs to be reduced. UCC24612 resets the minimum off blanking time clamp to the absolute

minimum of 400 ns to allow full conduction of the SR on the subsequent cycles.

If for any reason the off blanking time expires after the SR body diode conduction, the SR turn-on is skipped for

the switching cycle. This is because when the SR conducts, it conducts with a minimum on-time, if the blanking

time expires at the end of the SR conduction time and converter operates in the CCM condition, there is a good

chance to cause shoot-through and endanger the converter.

The off blanking time has a maximum value of tOFF_MAX at 3.68 µs.