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System engineers can now take advantage of amplifiers based on gallium-nitride (GaN) technology to generate higher output power levels in smaller physical systems. However, these GaN devices also require sufficient thermal management. In the white paper, "CW Operation of QFN-Packaged Pulsed GaN Power Amplifiers," Qorvo discusses thermal issues associated with using QFN-packaged GaN power amplifiers (PAs), originally designed for pulsed operation, in continuous-wave (CW) mode. Qorvo’s TGA2307-SM GaN PA is used as an example.
The white paper explains that many high-power, packaged GaN devices that were originally intended to be used in pulsed applications are also being considered for high-power CW systems, owing to these devices’ small size and weight. Proper thermal management of these GaN devices can be challenging due to several factors, such as the smaller package’s thermal footprint. One example of such a device is the TGA2307-SM PA, which was originally developed to be used primarily for pulsed applications. This PA is housed in a 6-×-6-mm, 40-pin QFN package.
Employing copper-filled thermal vias under the center pad of a package is one thermal-management technique. However, the white paper notes that this approach is not adequate for power levels exceeding the 10-to-15 W range. Printed-circuit-boards (PCBs) with openings for heat sinks with machined pedestals and coined PCBs are two solutions for higher-power dissipation applications. They allow for a much lower thermal resistance from the package through the PCB to the external heat sink.
To determine if the TGA2307-SM is well suited to be used in CW mode, three material stack-up environments are simulated. The first method utilizes 8-mil-filled thermal vias with the PCB epoxy-attached to a heat sink. The other two methods use a 20-mil coined PCB, which in both cases is also attached to a heat sink. However, two different approaches are taken for the PCB-to-heat-sink attachment, as one case uses epoxy, while the other uses solder. The results of all three thermal simulations are shown.
Qorvo Inc., 2300 NE Brookwood Pkwy., Hillsboro, OR 97124; (844) 890-8163