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 UCC2732x-Q1 family of drivers is available in two different packages to cover a range of application requirements.

The 8-pin SOIC (D) package has a power rating of approximately 0.5 W at T_A = 70°C. This limit is imposed in conjunction with the power derating factor also given in the table. The power dissipation in our earlier example is 0.432 W with a 10-nF load, 12-V V_DD, 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 8-pin MSOP PowerPAD (DGN) significantly relieves this concern by offering an effective means of removing the heat from the semiconductor junction. As illustrated in PowerPad Thermally Enhanced Package, 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 PCB directly underneath the package, reducing the θ_JC to 4.7°C/W. Data is presented in PowerPad Thermally Enhanced Package to show that the power dissipation can be quadrupled in the PowerPAD package when compared to the standard packages. The PCB must be designed with thermal lands and thermal vias to complete the heat removal subsystem, as summarized in PowerPAD Made Easy. 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.