UCC27523, UCC27524, UCC27525, UCC27526
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SLUSAQ3E –NOVEMBER 2011–REVISED JUNE 2012
Low Propagation Delays and Tightly Matched Outputs
The UCC2752x driver devices feature a best in class, 13-ns (typical) propagation delay between input and output
which goes to offer the lowest level of pulse transmission distortion available in the industry for high frequency
switching applications. For example in synchronous rectifier applications, the SR MOSFETs can be driven with
very low distortion when a single driver device is used to drive both the SR MOSFETs. Further, the driver
devices also feature an extremely accurate, 1-ns (typ) matched internal propagation delays between the two
channels which is beneficial for applications requiring dual gate drives with critical timing. For example in a PFC
application, a pair of paralleled MOSFETs may be driven independently using each output channel, which the
inputs of both channels are driven by a common control signal from the PFC controller device. In this case the
1ns delay matching ensures that the paralleled MOSFETs are driven in a simultaneous fashion with the minimum
of turn-on delay difference. Yet another benefit of the tight matching between the two channels is that the two
channels can be connected together to effectively increase current drive capability i.e. A and B channels may be
combined into a single driver by connecting the INA and INB inputs together and the OUTA and OUTB outputs
together. Then, a single signal can control the paralleled combination.
Caution must be exercised when directly connecting OUTA and OUTB pins together since there is the possibility
that any delay between the two channels during turn-on or turn-off may result in shoot-through current
conduction as shown in Figure 33. While the two channels are inherently very well matched (4-ns Max
propagation delay), it should be noted that there may be differences in the input threshold voltage level between
the two channels which can cause the delay between the two outputs especially when slow dV/dt input signals
are employed. The following guidelines are recommended whenever the two driver channels are paralleled using
direct connections between OUTA and OUTB along with INA and INB:
•
Use very fast dV/dt input signals (20 V/µs or greater) on INA and INB pins to minimize impact of differences
in input thresholds causing delays between the channels.
•
INA and INB connections must be made as close to the device pins as possible.
Wherever possible, a safe practice would be to add an option in the design to have gate resistors in series with
OUTA and OUTB. This allows the option to use 0-Ω resistors for paralleling outputs directly or to add appropriate
series resistances to limit shoot-through current, should it become necessary.
VDD
VDD
200 kW
200 kW
ENA
INA
1
2
8
7
ENB
ISHOOT-THROUGH
OUTA
VDD
Slow Input Signal
VIN_H
(Channel B)
VDD
400 kW
VIN_H
(Channel A)
VDD
VDD
UVLO
6
5
GND
INB
3
4
VDD
OUTB
400 kW
Figure 33. Slow Input Signal May Cause Shoot-Through Between Channels During Paralleling
(recommended dV/dt is 20 V/µs or higher)
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