Datasheet
SLUS486B − AUGUST 2001 − REVISED JULY 2003
6
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APPLICATION INFORMATION
predictive gate drive technique
The Predictive Gate Drive technology utilizes a digital feedback system to detect body-diode conduction, and
then adjusts the deadtime delays to minimize it. This system virtually eliminates the body-diode conduction time
intervals for the synchronous MOSFET, while adjusting for different MOSFETs characteristics, propagation and
load dependent delays. Maximum power stage efficiency is the end result.
Two internal feedback loops in the predictive delay controller continuously adjusts the turn on delays for the two
MOSFET gate drives G1 and G2. As shown in Figure 2, t
ON,G1
and t
ON,G2
are varied to provide minimum
body-diode conduction in the synchronous rectifier MOSFET Q
2
. The turn-off delay for both G1 and G2, t
OFF,G1
and t
OFF,G2
are fixed by propagation delays internal to the device.
The predictive delay controller is implemented using a digital control technique, and the time delays are
therefore discrete. The turn-on delays, t
ON,
G1
and t
ON,
G2
, are changed by a single step (typically 3 ns) every
switching cycle. The minimum and maximum turn-on delays for G1 and G2 are specified in the electrical
characteristics table.
t
OFF,G1
t
OFF,G2
t
ON,G1
t
ON,G2
G1
G2
3.25 V
10%
90%
90%
10%
3.25 V
UCC37222
UCC27221
IN
Figure 2. Predictive Gate Drive Timing Diagram