Detailed PCB and Cooler Design for AMD Radeon RX 7900 XTX
Instead of a first-party product with limited availability like the NVIDIA Founders Edition, AMD’s Radeon RX 7900 XTX reference-design is a traditional reference-design that is marketed by AMD’s add-in board partners under their brand (without sticking their own labels on the product). Internally, reference-design cards are referred to as “MBA cards” by AMD and its partners (made by AMD cards). The business provided us with a technical rundown of the PCB’s reference design. The RX 7900 XTX PCB offers a high-quality selection of components, just like every reference AMD PCB for the previous several generations. The card has a pricey 14-layer PCB that includes 4 extra layers made of 2-oz copper. Graphics cards typically have PCB layer counts of around 10, and enterprise-grade products often have 14-layer PCBs. In addition, ITEQ IT-170GRA epoxy and laminate materials are used on the PCB, allowing for a glass transition temperature (Tg) of 175 °C (the GPU won’t get nearly as hot).
Two 8-pin PCIe power connections are used to supply power to the RX 7900 XTX PCB in the standard design. When you include the 150 W input from the two connections and the 75 W from the PCIe slot, the RX 7900 XTX’s average board power rating of 355 W fits within the 375 overall power-draw capabilities. AMD made an effort to reduce power spikes, at least from the PCIe slot. Any excursions should stay within the 8-pin power connectors. The card uses “high efficiency” DrMOS power-stage phases for a 20-phase VRM system (could be very high current). Given the “Navi 31” GPU’s 384-bit memory interface, 12 GDDR6 memory chips surround it. On the 320-bit memory interface-equipped RX 7900 XT, two of these memory pads can go unused. Two standard-size DisplayPort 2.1, one USB type-C with DisplayPort passthrough, and one HDMI 2.1a are among the RX 7900 series’ display outputs.
Three fans with independent speed controls and intake air temperature sensors are axially ventilated by the cooling system’s aluminum fin-stack heatsink. The backplate and cooler shroud are composed of die-cast aluminum. The primary heatsink uses a massive stack of aluminum fins to which a vapor chamber plate transfers heat. The GPU, memory chips, and VRM generate heat that is drawn into the vapor chamber and base plate. A secondary heatspreader strengthens the card’s structure while drawing heat from other smaller heat sources. The vapor chamber plate in the RX 6950 XT RDNA2 reference-design, according to AMD, is 10% bigger. For the GPU and memory chips as well as an “ultra soft” thermal pad for the VRM MOSFETs, the company is introducing a more modern thermal interface material (TIM).
The RX 7900 XTX reference design card turns out to be physically larger than the RX 7900 XT reference design (if it does exist in production). The RX 7900 XT is closer to being a typical “full-height” add-in board than the reference RX 7900 XTX, which is 28.7 cm long and 12.3 cm tall. Each card measures 2.5 slots thick. The RX 7900 XT is small because the cooler must manage a typical board power of 300 W, which is 15% less than the RX 7900 XTX’s 355 W.
