DEIC420 Datasheet, PDF (7/7 Pages) IXYS Corporation – 20 Ampere Low-Side Ultrafast RF MOSFET Driver

APPLICATIONS INFORMATION
DEIC420
High Frequency Gate Drive Circuit
The circuit diagram in figure 17 is a circuit diagram for a
very high switching speed, high frequency gate driver
circuit using the DEIC420. This is the circuit used in the
EVIC420 Evaluation Board,and is capable of driving a
MOSFET at up to the maximum operating limits of the
DEIC420. The circuit's very high switching speed and
high frequency operation dictates the close attention to
several important issues with respect to circuit design.
The three key elements are circuit loop inductance, Vcc
bypassing and grounding.
Circuit Loop Inductance
Referring to Figure 17, the Vcc to Vcc ground current
path defines the loop which will generate the inductive
term. This loop must be kept as short as possible. The
output lead must be no further than 0.375 inches
(9.5mm) from the gate of the MOSFET. Furthermore the
output ground leads must provide a balanced symmetric
coplanar ground return for optimum operation.
Vcc Bypassing
In order for the circuit to turn the MOSFET on properly,
the DEIC420 must be able to draw up to 20A of current
from the Vcc power supply in 2-6ns (depending upon the
input capacitance of the MOSFET being driven). This
means that there must be very low impedance between
the driver and the power supply. The most common
method of achieving this low impedance is to bypass the
power supply at the driver with a capacitance value that
is at least two orders of magnitude larger than the load
capacitance. Usually, this is achieved by placing two or
three different types of bypassing capacitors, with
complementary impedance curves, very close to the
driver itself. (These capacitors should be carefully
selected, low inductance, low resistance, high-pulse
current-service capacitors). Care should be taken to
keep the lengths of the leads between these bypass
capacitors and the DEIC420 to an absolute minimum.
The bypassing should be comprised of several values of
chip capacitors symmetrically placed on ether side of
the IC. Recommended values are .01uF, .47uF chips
and at least two 4.7uF tantalums.
Grounding
In order for the design to turn the load off properly, the
DEIC420 must be able to drain this 20A of current into
an adequate grounding system. There are three paths for
returning current that need to be considered: Path #1 is
between the DEIC420 and its load. Path #2 is between
the DEIC420 and its power supply. Path #3 is between
the DEIC420 and whatever logic is driving it. All three of
these paths should be as low in resistance and
inductance as possible, and thus as short as practical.
Output Lead Inductance
Of equal importance to supply bypassing and grounding
are issues related to the output lead inductance. Every
effort should be made to keep the leads between the
driver and its load as short and wide as possible, and
treated as coplanar transmission lines.
In configurations where the optimum configuration of
circuit layout and bypassing cannot be used, a series
resistance of a few Ohms in the gate lead may be
necessary to prevent ringing.
Heat Sinking
For high power operation, the bottom side metalized
substrate should be placed in compression against an
appropriate heat sink. The substrate is metalized for
improved heat dissipation, and is not electrically
connected to the device or to ground.
See the DEI technical note "DE-Series MOSFET and IC
Mounting Instructions" on the DEI web site at
www.directedenergy.com/apptech.htm for detailed
mounting instructions. The package dimensions of the
DEIC420 are identical to those of the DE-275 MOSFET.
Directed Energy, Inc.
An IXYS Company
2401 Research Blvd. Ste. 108, Ft. Collins, CO 80526
Tel: [phone]; Fax: [phone]
e-mail: [e-mail]
www.directedenergy.com
Doc #9200-0230 Rev 2
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