The UCC27524 driver device features a very small, 17-ns (typical) propagation delay between input and output, which offers the lowest level of pulse width distortion for high-frequency switching applications. For example, in synchronous rectifier applications, the SR MOSFETs are driven with very low distortion when a single driver device is used to drive the SR MOSFETs. Additionally, the driver devices also feature extremely accurate, 1-ns (typical) matched internal propagation delays between the two channels, which is beneficial for applications that require dual gate drives with critical timing. For example, in a PFC application, a pair of paralleled MOSFETs can be driven independently using each output channel, with the inputs of both channels driven by a common control signal from the PFC controller. In this case, the 1-ns delay matching ensures that the paralleled MOSFETs are driven in a simultaneous fashion, minimizing turn-on and turn-off delay differences. Another benefit of the tight matching between the two channels is that the two channels can be connected together to effectively double the drive current capability. That is, 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 controls the paralleled power devices.

Caution must be exercised when directly connecting OUTA and OUTB pins together because there is the possibility that any delay between the two channels during turnon or turnoff may result in shoot-through current conduction as shown in Figure 7-2. While the two channels are inherently very well matched (2-ns Max propagation delay), note that there may be differences in the input threshold voltage level between the two channels which causes 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.

Figure 7-2 Slow Input Signal Can Cause Shoot-Through Between Channels During Paralleling (Recommended DV/DT is 20 V/Μs or Higher)