Datasheet

UCC27321-Q1, UCC27322-Q1

SLUSA13C –FEBRUARY 2010–REVISED MARCH 2012

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Thermal Information

The useful range of a driver is greatly affected by the drive-power requirements of the load and the thermal

characteristics of the package. For a power driver to be useful over a particular temperature range, the package

must allow for the efficient removal of the heat produced while keeping the junction temperature within rated

limits. The UCC27321/2 family of drivers is available in two different packages to cover a range of application

requirements.

As shown in Power Dissipation Ratings, the SOIC-8 (D) package has a power rating of approximately 0.5 W at

= 70°C. This limit is imposed in conjunction with the power derating factor also given in the table. Note that

the power dissipation in our earlier example is 0.432 W with a 10-nF load, 12-V V

, switched at 300 kHz. Thus,

only one load of this size could be driven using the D package. The difficulties with heat removal limit the drive

available in the older packages.

The MSOP PowerPAD package (DGN) significantly relieves this concern by offering an effective means of

removing the heat from the semiconductor junction. As illustrated in Reference 3, the PowerPAD packages offer

a lead-frame die pad that is exposed at the base of the package. This pad is soldered to the copper on the PC

board directly underneath the package, reducing the θ

to 4.7°C/W. Data is presented in Reference 3 to show

that the power dissipation can be quadrupled in the PowerPAD package when compared to the standard

packages. The PC board must be designed with thermal lands and thermal vias to complete the heat removal

subsystem, as summarized in Reference 4. This allows a significant improvement in heatsink capability over that

available in the D package and is shown to more than double the power capability of the D package.

NOTE

The PowerPAD thermal pad is not directly connected to any leads of the package.

However, it is electrically and thermally connected to the substrate, which is the ground of

the device.

References

1. Power Supply Seminar SEM-1400 Topic 2: Design And Application Guide For High Speed MOSFET Gate

Drive Circuits, Laszlo Balogh (SLUP133)

2. Practical Considerations in High Performance MOSFET, IGBT and MCT Gate Drive Circuits, Bill Andreycak

(SLUA105)

3. PowerPad Thermally Enhanced Package (SLMA002)

4. PowerPAD Made Easy (SLMA004)