DEIC515 Datasheet, PDF (8/9 Pages) IXYS Corporation – 15 Ampere Low-Side Ultrafast RF MOSFET Driver

Application Information
DEIC515
15 Ampere Low-Side Ultrafast RF MOSFET Driver
Introduction
Circuits capable of very high switching speeds and
high frequency operation require close attention to
several important issues. Key elements include circuit
loop inductance, Vcc bypassing, and grounding.
Circuit Loop Inductance
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 to turn a MOSFET on properly, the DEIC515
must be able to draw up to 15A of current from the
Vcc power supply in 2-6ns (depending upon the input
capacitance of the MOSFET being driven). Good per-
formance requires 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 much larger than the load capacitance. Usually,
this is achieved by placing two or three different types
of bypassing capacitors, with complementary imped-
ance curves, very close to the driver itself. (These ca-
pacitors 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 DEIC515 to
an absolute minimum.
The bypassing should be comprised of several values
of chip capacitors symmetrically placed on either side
of the IC. Recommended values are .01uF and .47uF
chips and at least two 4.7uF tantalums.
Grounding
In order for the design to turn the load off properly, the
DEIC515 must be able to drain this 15A of current into
an adequate grounding system. There are two paths
for returning current that need to be considered: Path
#1 is between the DEIC515 and its load, and path #2
is between the DEIC515 and its power supply. Both of
these paths should be as low in resistance and induc-
tance as possible, and thus as short as practical.
The DEI515 has separate ground leads for input and
power which allows the addition of a common mode
choke at the input and input ground leads.
The common mode choke will provide a means of pre-
venting ground bounce from affecting the input to the
driver. The selection of the common mode choke is re-
lated to the device being driven, the board layout, and the
Vcc bypassing.
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 cir-
cuit layout and bypassing cannot be used, a series resis-
tance of a few ohms in the gate lead may be necessary to
prevent ringing.
Heat Sinking
For high power operation, the bottom side metalized sub-
strate should be placed in compression against an appro-
priate 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 IXYSRF website at
www.ixysrf.com for detailed mounting instructions.