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Each power deliver has its very own boundaries, and the same applies to huge bandgap (WBG) technology along with gallium nitride (GaN) transistors. But what ought to be executed if the circuit has to procedure more electricity than may be supported through a unmarried tool? One alternative for designers is to run devices in parallel, which almost doubles the throughput of a single tool. As with their silicon ancestors, the practical implementation of the parallel use of GaN-HEMT additives is extra complicated than the concept suggests.
The first assignment is to make sure that the equal modern is
flowing thru every device. While RDS (on) is different between transistors,
matched additives can be required to make sure an evenly matched static modern.
The second trouble is dynamic switching as each device has a barely one of a
kind threshold when it's miles turned on and rancid. This not only leads to an
asymmetrical modern distribution, however also can lead to undesirable
high-frequency oscillations. In the worst case, they can wreck GaN gadgets.
Driving GaN
HEMT
The manage circuit for GaN HEMT additives differs extensively
from the circuit used for conventional silicon MOSFETs. Infineon CoolGaN ™
transistors require greater than twice the ahead voltage VF to interchange on.
After switching on, the desk bound gate voltage drops lower back to VF. In
hard-switching applications, a negative voltage of approx. –2.Five V is
required to interchange off the transistor. Fortunately, devices like the
EiceDRIVER ™ 1EDI20N12AF make it easy to enforce a primary control circuit
(Figure 1). With a parallel pressure implementation, each CoolGaN ™ HEMT has
its very own control circuit.
simplifies
the implementation of the force.
Even with this technique, there's still a common current
direction that disrupts the gate driver loops. This is due to currents flowing
along the path of the Kelvin Source. If the impedances on those paths are not
same, this will cause distinct VGS voltages within the CoolGaN ™ HEMT gate
circuits. Just a few mV can lead to an asymmetrical present day distribution of
several amperes and large fluctuations while switching.
General
mode enhancements
Placing a commonplace mode inductance (CM) in the Kelvin
source route effects in a high impedance within the commonplace current path,
even as best a low leakage inductance is discovered inside the gate driver
direction (Figure 1). This consequences in a giant discount in oscillation
(Figure 2), even though the choice of inductor must be cautiously selected to
limit the impact on gate drive overall performance.
The use of a CM inductance in the Kelvin source path
substantially reduces the oscillation when switching the parallel HEMT CoolGaN
™.
Parasites due to PCB layout, strains, and layering are also a
not unusual hassle with such designs. For CoolGaN ™ HEMT, the principle mission
is to make certain the stability of the VGS thresholds and viable RDS
variations (on) between devices. SIMetrix simulations have proven that any
static imbalance in parallel CoolGaN ™ designs is only due to (and including)
variations inside the RDS. If this is seen as a trouble, tool pairing may be
executed. As mentioned in advance, using a CM inductor removes adverse vibrations.
Otherwise, only a accurate board format is needed for a dependable layout, as
an instance keeping the strength loops small and symmetrical and coffee
parasitic parameters of the switching nodes.
Experiments
with parallel CoolGaN ™
While the simulation offers treasured insights, trying out
real gadgets within the laboratory enables evaluation in reference to real
packages. To meet this need, Infineon offers an IGOT60R070D1 CoolGaN ™ 70 mΩ
quad strength transistor parallel half bridge assessment board. Designed
according to the tips mentioned right here, it is a exquisite start line for
step-down or step-up testing with an external inductor. Hard and smooth
switching at frequencies up to one MHz and strength levels of several kW are
supported, and the output voltage is constrained to 450 V via a particular
integrated one hundred μF capacitor. With a appropriate heat sink, continuous
currents of 28 A and peak currents of 70 A may be carried out. The dead time
can also be set using the integrated potentiometer.
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