PCB layout and components of the Radeon RX 7900 XTX
AMD hasn’t cut all the old ties, as the RDNA3 architecture’s power supply once again relies on VDDCR_GFX (i.e. the equivalent of NVIDIA’s NVVDD) as the largest item for the GPU itself. For this purpose, 12 phases are used, each of which controls a voltage regulator. In addition, we find the well-known VDD_SoC with 3 phases and one voltage regulator per phase, as well as VDDCR_USR. This is a new addition and relies on 2 phases and therefore 2 voltage regulators. In addition there are 2 phases (2 voltage regulators) for VDD_MEM (i.e. the memory) and a single buck converter for VDDCI_MEM.
The generation of VDDCI_MEM is not a big item performance-wise, but it is enormously important. It is used for the GPU-internal level transition between the GPU and the memory signal, something like the voltage between the memory and the GPU core on the I/O bus. In addition, one still generates a constant source for 0.75 volts. The majority of these very similar voltage transformers are located on the front of the board. There is also a 1.8V source (TTL, GPU GPIO), VDD_13 (Aux) and an ultra-low dropout chip generates the very low voltage for the PLL area (VPP).
Two PWM controllers for the generation of the most important phases sit on the back in the upper left third of the board, a weirerer one on the upper right. AMD relies on Monolith’s top products this time, just like NVIDIA did for the reference cards. The first rail of the MP2857 is used for the 12 phases of the VDDCR_GFX, the second rail for the generation of the VDD_MEM. It is a digital, multi-phase, dual-rail controller that primarily provides power to PWM VID cores and is also compatible with the AVSBus interface. The MP2857 can (and should) also work with Monolith’s Intelli-Phase products to complete the multi-phase voltage regulator (VR) solution with a minimum of external components. The both slightly smaller and unfortunately also from the data not publicly available MP2856 are then responsible for VDDCI, VDD_SoC and VDDCR_USR.
All power stages used, including those for the memory, are also Monolith products. The MP87997 is also not freely documented, but it should be a very capable monolithic half-bridge. The integration of drivers and MOSFETs (DrMOS) results in high efficiency due to optimal dead time and reduction of parasitic inductance. This small, 5 mm x 6 mm LGA device is a perfect fit for the MP2857 and MP2856.
PCB layout and components of the Radeon RX 7900 XT
In principle, the XT’s board is a slightly simplified version of the XTX board. Here we also find VDDCR_GFX. For this, only 10 instead of 12 phases are used, each of which then controls a single voltage regulator. VDD_SoC shrinks to 2 instead of 3 phases and one voltage regulator per phase, and VDDCR_USR with 2 phases and thus also 2 voltage regulators. In addition there are again the 2 phases resp. 2 voltage regulators for VDD_MEM and a single buck converter for VDDCI_MEM (was already explained above). In addition, you also generate a constant source for 0.75 volts on the XT, as well as a 1.8V source (TTL, GPU GPIO), the VDD_13 (Aux) and a VPP generated by an ultra-low dropout chip.
The two PWM controllers for the generation of the most important phases are again located on the rear side in the upper left third of the board, onother one on the upper right.
The components used are identical on both boards including the 150 mH coils for the voltage regulators and the 190 mH series chokes for filtering on the 12V rails, also the single BIOS and various smaller buck converters. In addition, there is an MCU for all the control tasks and of course the 12 or 10 RAM modules from SKhynix with the 20 Gbps.
- 1 - Introduction, technical data and technology
- 2 - Test system with the igor'sLAB PC from MIFCOM
- 3 - Teardown: PCB and Components
- 4 - Teardown: Cooler and disassembly help
- 5 - Summary gaming performance WQHD (2560 x 1440)
- 6 - Summary gaming performance Ultra-HD (3840 x 2160)
- 7 - Single charts for WQHD (2560 x 1440)
- 8 - Single charts for Ultra-HD (3840 x 2160)
- 9 - Workstation graphics and rendering
- 10 - Power consumption in detail and load balancing
- 11 - Transients, limits and PSU recommendation
- 12 - Clock rates, temperatures and infrared
- 13 - Fan speed and Noise
- 14 - Summary and conclusion
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