The large-area contacts combined with the copper housing significantly improve heat dissipation compared to a SOIC plastic molded package: the junction-to-PCB thermal resistance is reduced to less than 1°C/W, compared to 20°C/W for a standard SO-8 package. The copper housing provides a heatsink surface, improving top junction-to-case thermal resistance to only 1.4°C/W compared to 18°C/W for an SO-8.

With the use of heat sink and cooling airflow, the DirectFET package dissipates 50% more heat out of the top of the package, reducing operating temperature by up to 50oC and enabling more then double current ratings. The difference between DirectFET and Bottomless SO-8 or Leadless SO-8 is even greater when comparing topside cooling effectiveness. High top R_th(J-C) explains why standard and enhanced SO-8 packages are only used with single-side cooling through the PCB. Effective topside cooling means that dissipated heat can be pulled directly into a heat sink away from the circuit board, increasing the currents that the device can safely carry.

Packaging improves electrical efficiency: At 20A, the DirectFET package without a heatsink and still air demonstrate 3% higher efficiency than the SO-8 circuit under identical conditions. (See Figure 2.)

Figure 2. Efficiency vs. Output Current

Packaging reduces inductance and improves performance at higher frequency: The DirectFET package construction minimized inductance, which is important for high-frequency DC-DC power conversion circuits in high current, multi-phase applications. Two DirectFETs deliver twice as much current at 2MHz compare to two SO-8s at the same frequency. (See Figure 3.) Ringing is also significantly reduced at high frequency. (See Figure 4.)

Figure 3. Efficiency improves significantly at higher frequency with DirectFET