Power MOSFET Cooling Reaches the Top

Feb 1, 2010 12:00 PM
Davis, Sam, PET

An upgraded structure produces MOSFETs with an exposed metal source on top, providing top-side as well as conventional bottom-side cooling.

The DualCool^™ NexFET^™ power MOSFETs from Texas Instruments feature a novel design that enables heat dissipation through the top of the device, as well as through the more traditional bottom side. The standard-footprint power MOSFETs are claimed to offer up to 80% higher power dissipation and handle up to 50% more current than standard devices. Compared with existing packages, these power MOSFETs can reduce the number of FETs needed to achieve higher current levels.

UNCOVERING THE DualCool NexFET DEVICES

The ability to improve power dissipation was made possible by the DualCool's packaging concept, in which the source connection is brought out to the top of the package as an exposed metal plate. Thus, a heat sink may be attached to the source plate via an isolated thermal pad.

Fig. 1 shows the internal construction of the MOSFET package. Fig. 2 is a plot comparing thermal performance of the DualCool MOSFET's with performance found in other packages.

Besides better cooling, the NexFET's silicon structure reduces the MOSFET's parasitic capacitances. The structure minimizes drive requirements by cutting total gate charge (Q_G), enabling the MOSFETs to switch at higher frequencies than their predecessors.

DualCool FEATURES

Features of the DualCool family include:

• Single-phase 35-A synchronous buck converter MOSFETs, using single MOSFETs for both the high- and low-side switches in high-current dc-dc applications
• Efficient dual-side heat-sinking offering designers the flexibility to use higher-current processors without increasing end-equipment size
• Industry-standard SON 5- × 6-mm footprint eases design and keeps cost down, saving 30 mm² compared to using two standard packages

Texas Instruments produces NexFETs in both the DualCool version as well as a standard version that does not provide top-side cooling. Both versions have the same footprint. If necessary, the enhanced DualCool version can replace the standard version without requiring any PCB layout changes.

The DualCool NexFETs (See the Table) allow computing and telecom system designers to use higher-current processors with expanded memory while saving board space. These MOSFETs can be used in many applications such as desktop PCs, servers, networking equipment, base stations, and high-current industrial systems.

DualCool NexFET MOSFET FAMILY FEATURES

PART NO.	SIZE (mm)	VDS(V)	TYPICAL VGS(th) (V)	RDS(ON) at 4.5 V (mΩ)	QG (nC)	FIGURE OF MERIT
CSD16407Q5C	5 × 6	25	1.6	2.5	13.3	33.25
CSD16408Q5C	5 × 6	25	1.6	5.4	6.5	35.10
CSD16325Q5C	5 × 6	25	1.1	1.7	18.0	30.60
CSD16321Q5C	5 × 6	25	1.1	2.1	14.0	29.40
CSD16322Q5C	5 × 6	25	1.1	4.5	6.5	29.25

SOURCE OF NexFET POWER MOSFET TECHNOLOGY

IN FEB. 2009, Texas Instruments acquired the Bethlehem, PA-based CICLON Semiconductor Device Corp., a producer of high-frequency, high-efficiency power-management semiconductors. The acquisition expanded TI's capability to improve energy efficiency in today's end-equipment designs, including high-power computing and server systems. CICLON's state-of-the-art NexFET™ technology, coupled with DualCool™ packaging technology, attains performance and size improvements by delivering a dramatic reduction in gate charge as well as its lower thermal resistance package.

At the time of the purchase, CICLON (pronounced See-Clone) was a fabless provider of power MOSFET RF LDMOS and semiconductor products for high-performance applications. With this addition, Texas Instruments may now be the only company that produces discrete semiconductors, ICs, and complete plug-in card power supplies.

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