LMG3410 Datasheet, PDF (10/33 Pages) Texas Instruments – 600-V 12-A Single Channel GaN Power Stage

LMG3410
SNOSD10A – APRIL 2016 – REVISED JUNE 2016
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Switching Parameters (continued)
7.1.1 Turn-on Delays
The timing of the turn-on transition is broken into three components: propagation delay, turn-on delay and rise
time. The first component is the propagation delay of the driver from when the input goes high to when the GaN
FET starts turning on. The turn-on delay is the delay from when the FET starts turning on (represented by 1 A
drain current) to when the drain voltage swings down by 20 percent. Finally, the rise time is the time it takes the
drain voltage to slew between 80 percent and 20 percent of the bus voltage. The drive-strength resistor value
has a large effect on turn-on delay and rise time but does not affect the propagation delay significantly.
The propagation delay specification is comparable to MOSFET drivers while the turn-on delay and the rise time
are comparable to the respective MOSFET specifications. Note that per industry standards, the fall time of the
drain-source voltage is called rise time.
7.1.2 Turn-off Delays
The timing of the turn-off transition is similarly broken into three components: propagation delay, turn-off delay
and fall time. The first component is the propagation delay of the driver from when the input goes low to when
the GaN FET starts turning off. The turn-off delay is the delay from when the FET starts turning of (represented
by the drain rising above 10 V) to when the drain voltage swings up by 20 percent. Finally, the fall time is the
time it takes the drain voltage to slew between 20 percent and 80 percent of the bus voltage. The turn-off delays
of the LMG3410 are independent of the drive-strength resistor but the turn-off delay and the fall time are heavily
dependent on the load current.
The propagation delay specification is comparable to MOSFET drivers while the turn-off delay and the fall time
are comparable to the respective MOSFET specifications. Note that per industry standards, the rise time of the
drain-source voltage is called fall time.
7.1.3 Drain Slew Rate
The slew rate, measured in volts per nanosecond, is measured on the turn-on edge of the LMG3410. The slew
rate is considered over the rise time, where the drain falls from 80 percent to 20 percent of the bus voltage. The
drain slew rate is thus given by 60 percent of the bus voltage divided by the rise time. This drain slew rate is
dependent on the RDRV value and is only slightly affected by drain current.
7.1.4 Turn-on and Turn-off Energy
The turn-on and turn-off energy, shown in Figure 7, represent the energy absorbed by the low-side device during
the turn-on and turn-off transients of the circuit in Figure 9, respectively. As this circuit represents a synchronous
buck converter, with input shorted to output, the switching energy is dissipated in the low-side device. The turn-
on transition is lossy, while the turn-off transition is essentially lossless; the output capacitance of the devices is
charged by the inductor current. The turn-on and turn-off losses have been calculated from experimental
waveforms by integrating the product of the drain current with the drain-source voltage over the turn-on and turn-
off times, respectively.
The switching loss of the converter can be determined by adding the turn-on and turn-off energy in Figure 7,
adjusting for the R_DRV value (shown in Figure 8). To obtain the switching loss, multiply this value by the switching
frequency. The obtained loss is a sum of the V-I overlap loss (due to hard switching) and the loss caused by
charging and discharging the C_OSS of both devices. Additional test-fixture capacitance, including PCB and
inductor intra-winding capacitance, has not been removed from these measurements.
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