Datasheet DEIC420 (IXYS) - 7

DEIC420 APPLICATIONS INFORMATION High Frequency Gate Drive Circuit
The circuit diagram in figure 17 is a circuit diagram for a the DEIC420 and whatever logic is driving it. All three of very high switching speed, high frequency gate driver these paths should be as low in resistance and circuit using the DEIC420. This is the circuit used in the inductance as possible, and thus as short as practical. EVIC420 Evaluation Board,and is capable of driving a
Output Lead Inductance
MOSFET at up to the maximum operating limits of the Of equal importance to supply bypassing and grounding DEIC420. The circuit's very high switching speed and are issues related to the output lead inductance. Every high frequency operation dictates the close attention to effort should be made to keep the leads between the several important issues with respect to circuit design. driver and its load as short and wide as possible, and The three key elements are circuit loop inductance, Vcc treated as coplanar transmission lines. bypassing and grounding. In configurations where the optimum configuration of
Circuit Loop Inductance
circuit layout and bypassing cannot be used, a series Referring to Figure 17, the Vcc to Vcc ground current resistance of a few Ohms in the gate lead may be path defines the loop which will generate the inductive necessary to prevent ringing. term. This loop must be kept as short as possible. The output lead must be no further than 0.375 inches
Heat Sinking
(9.5mm) from the gate of the MOSFET. Furthermore the For high power operation, the bottom side metalized output ground leads must provide a balanced symmetric substrate should be placed in compression against an coplanar ground return for optimum operation. appropriate heat sink. The substrate is metalized for
Vcc Bypassing
improved heat dissipation, and is not electrically In order for the circuit to turn the MOSFET on properly, connected to the device or to ground. the DEIC420 must be able to draw up to 20A of current See the DEI technical note "DE-Series MOSFET and IC from the Vcc power supply in 2-6ns (depending upon the Mounting Instructions" on the DEI web site at input capacitance of the MOSFET being driven). This www.directedenergy.com/apptech.htm for detailed means that there must be very low impedance between mounting instructions. The package dimensions of the the driver and the power supply. The most common DEIC420 are identical to those of the DE-275 MOSFET. 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 Directed Energy, Inc. returning current that need to be considered: Path #1 is An IXYS Company between the DEIC420 and its load. Path #2 is between 2401 Research Blvd. Ste. 108, Ft. Collins, CO 80526 Tel: 970-493-1901; Fax: 970-493-1903 the DEIC420 and its power supply. Path #3 is between e-mail: [email protected] www.directedenergy.com Doc #9200-0230 Rev 3 7