For a DC/DC module 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 TPSM64406 module is available in a small 6.5-mm × 7.55-mm 28-pin QFN package to cover a range of application requirements. The Section 6.4 table summarizes the thermal metrics of this package with related detail provided by the Semiconductor and IC Package Thermal Metrics application note.

The 28-pin QFN package offers a means of removing heat through the exposed thermal pads at the base of the package. This design allows a significant improvement in heat sinking. Designing the PCB with thermal lands, thermal vias, and one or more grounded planes is imperative to complete the heat removal subsystem. The exposed pads of the TPSM64406 are soldered to the ground-connected copper lands on the PCB directly underneath the device package, reducing the thermal resistance to a very low value.

Preferably, use a four-layer board with 2-oz copper thickness for all layers to provide low impedance, proper shielding and lower thermal resistance. Numerous vias with a 0.3-mm diameter connected from the thermal lands to the internal and solder-side ground planes are vital to promote heat transfer. In a multilayer PCB stack-up, a solid ground plane is typically placed on the PCB layer below the power-stage components. Not only does this design provide a plane for the power-stage currents to flow, but the design also represents a thermally conductive path away from the heat-generating device.