International Rectifier - DirectFET Product Information

DirectFET®; MOSFET Impedance Modeling and Testing

DirectFET Theoretical Model Under DC Conditions

Assumptions:

Breakdown DirectFET into rectangular plates
Rdc = ρL/(w X h)
Where:
ρ=resistivity
L=length
w X h=area of the cross-section of the conductor
Single ended drain connection

Package AC Impedance testing

Test cards placed as close as possible to LCR O/P to limit stray pick up
No moveable wires/Kelvin wires required to limit variation in short and open circuit measurements
Separate DUT and short circuit cards for each package…

Test Card Design: DirectFET®; MOSFET Example Gate, source and drain sense contacts on underside of board
Open circuit measurement card	Short circuit card	Device under test (DUT) card

D²Pak
4x15 mil
Al wires

D-Pak
2 x 8 mil
Al wires

SO-8
14 x 2 mil
Au wires

MLP
16 x 2 mil
Au wires

DirectFET
Cu ‘dummy’ die
3.3 x 2.0 mm

= location of Kelvin voltage sense connections

Effect of packaging parasitics upon 2-phase 1U VRM circuit efficiency

Lower package parasitics and and improved cooling results in 4% increase in converter efficiency at 2MHz

"Play Audio

Switching Waveforms in 2-Phase 1U VRM
DirectFET Waveform	SO-8 Waveform
30A VRM output current 500 KHz per phase Silicon of the near identical active area, voltage and generation used in both packages Inductance related ringing greater in case of SO-8
"Play Audio
IR’s proprietary DirectFET®; technology is covered by US Patent 6,624,522 and other US and foreign pending patent applications.


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