DirectFET® MOSFET: High Frequency Application Example
Increasing Frequency in Voltage Regulators for Advanced CPUs
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Today
- Voltage regulator operates at 300 to 500kHz
- Large capacitor bank is used to meet transient response
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Tomorrow
- Transient Response increases to ~400A/µs
- Load line decreases to sub-mOhm level
- Capacitor bank would be very large to meet both load line and transient response
- To avoid large capacitor bank voltage regulator must operate at higher Frequency: 1 to 2 MHz
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DirectFET MOSFET For High Frequency Buck Converters
- Voted in 2003 as the industry best RDS(on) in SO-8 footprint at 30V 2.7 mOhm typ.
- Up to 50% lower than comparable SO-8 device on the market
- Lower than comparable MOSFET in proprietary SO-8 derivative products
- Ultra-low gate-to-drain charge QGD - 16nC
- Dual-sided cooling
- Lowers operating temp
- Helps reduce PCB size
- Up to 70% lower package inductance
- Optimized for sync FET position
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DirectFET Package Designed for Power Semiconductor |
DirectFET Package Offers
- No Lead frame
- No wire bonds
- No bumped die
- Source & gate connections soldered directly on PCB
- 70% lower inductance
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| Parameter |
Unit |
DirectFET |
SO-8 |
| Package Resistance |
mΩ |
0.1 |
1.6 |
| Thickness |
mm |
0.7 |
1.75 |
RØj-pcb
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°C/W |
1 |
20 |
RØj-case
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°C/W |
3 |
18 |
| Inductance L |
nH |
0.6 |
2 |
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40% More Current at Similar Temperature |
SO-8 MOSFETs, 36.5A load @ 425LFM, Max SO-8 case temp is 100°C
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2-phase syn-buck, at 20 A/phase, Vin = 12V, Vout = 1.7 volts, frequency varies.
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DirectFET MOSFET vs. SO-8 at 2MHz
2 DirectFET MOSFETs deliver 2x as much current as 2 SO-8 at 2MHz
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Reduced Ringing At High Frequencies |
Substantial ringing with SO-8 MOSFETs at 2MHz
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Reduced ringing when used IRF6607/IRF6604 at 2MHz
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DirectFET MOSFET vs. SO-8 vs. Frequency
DirectFET MOSFETs are more efficient because the impedance is lower at
higher frequencies.
2-phase syn-buck, at 20 A/phase, Vin = 12V, Vout = 1.7 volts, frequency varies.
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The DirectFET MOSFET Advantage
2 DirectFET MOSFETs Deliver 30A/Phase @ 2MHz Frequency, @ 77% Efficiency
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Conclusions
- Elimination of wire bonds significantly increases efficiency above 1MHz doe to lower package impedance
- Increase in the amount of current carrying capability of the DirectFET MOSFET over more traditional packages
grows with frequency due to the combined effect of improved heat transfer plus lower impedance
- Higher efficiency plus higher current capability at high frequency operation produces the highest current
density available for powering up the newest high performance processors
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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