AMD Radeon RX 7900 XTX Reference Design PCB and Cooler Detailed

AMD Radeon RX 7900 XTX reference-design isn’t a first-party product with limited availability like the NVIDIA Founders Edition; but rather a classic reference-design that’s sold by AMD’s add-in board partners under their marquee (without sticking their own labels on the product). AMD and its partners internally refer to reference-design cards as “MBA cards” (made by AMD cards). The company gave us a technical overview of the reference-design PCB. As with every reference AMD PCB for the past several generations, the RX 7900 XTX PCB has a premium selection of components. The card uses an expensive 14-layer PCB with 4 additional layers of 2-oz copper. 14-layer PCBs are typically used with enterprise-grade products, and graphics cards typically tend to have PCB layer counts of around 10. The PCB also uses ITEQ IT-170GRA epoxy and laminate materials, which enable a glass transition temperature (Tg) of 175 °C (no, the GPU won’t get anywhere near as hot).

The reference-design RX 7900 XTX PCB draws power from two 8-pin PCIe power connectors. With the typical board power of the RX 7900 XTX rated at 355 W, this falls inside the 375 total power-draw capability when you add up the 150 W input from the two connectors, and 75 W from the PCIe slot. AMD worked to minimize power-draw spikes at least from the PCIe slot. Excursions, if any, should be localized to the 8-pin power connectors. The card features 20-phase VRM solution, using “high efficiency” DrMOS power-stage phases (could be very high current). The “Navi 31” GPU is surrounded by 12 GDDR6 memory chips given the GPU’s 384-bit memory interface. Two of these memory pads could end up unused on the RX 7900 XT, which has a 320-bit memory interface. Display outputs of the RX 7900 series include two standard-size DisplayPort 2.1, one USB type-C with DisplayPort passthrough; and one HDMI 2.1a.

The cooling solution features an aluminium fin-stack heatsink that’s ventilated axially by three fans that offer individual speed control and come with intake air temperature sensors. The cooler shroud and backplate are made of die-cast aluminium. The main heatsink uses a large aluminium fin-stack to which heat is drawn by a vapor-chamber plate. The vapor-chamber and base-plate pull heat from the GPU, memory chips, and VRM. A secondary heatspreader pulls heat from other minor heat sources and structurally reinforces the card. AMD says that the vapor chamber plate is 10% larger than the one in the RX 6950 XT RDNA2 reference-design. The company is introducing a newer thermal interface material (TIM) for the GPU and memory chips, and an “ultra soft” thermal pad for the VRM MOSFETs.

It turns out that the RX 7900 XTX reference design card is physically larger than the RX 7900 XT reference design (if it does exist in production). The reference RX 7900 XTX is 28.7 cm long and 12.3 cm tall; whereas the RX 7900 XT is 27.6 cm long, and 11.3 cm tall, making it closer to being a standard “full-height” add-in board. Both cards at 2.5-slot thick. The RX 7900 XT is compact as the cooler has to deal with a 15% lower typical board power of 300 W compared to 355 W for the RX 7900 XTX.