IXDN414SI Ver la hoja de datos (PDF) - IXYS CORPORATION
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IXDN414SI Datasheet PDF : 10 Pages
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IXDN414PI / N414CI / N414YI / N414SI
IXDI414PI / I414CI / I414YI / I414SI
Supply Bypassing, Grounding Practices and Output Lead inductance
When designing a circuit to drive a high speed
MOSFET utilizing the IXDN414/IXDI414, it is very
important to observe certain design criteria in
order to optimize performance of the driver.
Particular attention needs to be paid to Supply
Bypassing, Grounding, and minimizing the
Output Lead Inductance.
Say, for example, we are using the IXDN414 to
charge a 5000pF capacitive load from 0 to 25
volts in 25ns.
Using the formula: I= ∆V C / ∆t, where ∆V=25V
C=5000pF & ∆t=25ns we can determine that to
charge 5000pF to 25 volts in 25ns will take a
constant current of 5A. (In reality, the charging
current won’t be constant, and will peak
somewhere around 8A).
SUPPLY BYPASSING
In order for our design to turn the load on properly,
the IXDN414 must be able to draw this 5A of
current from the power supply in the 25ns. 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 a magnitude
larger than the load capacitance. Usually, this
would be achieved by placing two 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). Lead lengths may radiate at
high frequency due to inductance, so care should
be taken to keep the lengths of the leads between
these bypass capacitors and the IXDN414 to an
absolute minimum.
GROUNDING
In order for the design to turn the load off properly,
the IXDN414 must be able to drain this 5A of
current into an adequate grounding system. There
are three paths for returning current that need to
be considered: Path #1 is between the IXDN414
and its load. Path #2 is between the IXDN414 and
its power supply. Path #3 is between the IXDN414
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. In addition, every effort should be made
to keep these three ground paths distinctly
separate. Otherwise, the returning ground current
from the load may develop a voltage that would
have a detrimental effect on the logic line driving
the IXDN414.
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 it’s load as short
and wide as possible. If the driver must be placed
farther than 2” (5mm) from the load, then the output
leads should be treated as transmission lines. In
this case, a twisted-pair should be considered,
and the return line of each twisted pair should be
placed as close as possible to the ground pin of
the driver, and connected directly to the ground
terminal of the load.
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