9

IXDN414PI / N414CI / N414CM / N414YI / N414YM

IXDI414PI / I414CI / I414CM / I414YI / I414YM

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,

lowinductance,lowresistance,high-pulsecurrent-

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.

Supply Bypassing, Grounding Practices and Output Lead inductance