PCB Design and Specifications
In today’s graphics card engineering, it is the GPU’s memory subsystem configuration that determines the PCB wiring layout. Thus, the PCB for the GeForce GTX 260 Core 216 that uses the 55nm version of the G200 core would suit the GeForce GTX 275 just fine because both cards need a 448-bit memory bus and 14 chips of onboard GDDR3 memory. However, Nvidia has preferred to develop a new PCB for the new product.
The GeForce GTX 285, GeForce GTX 275 and GeForce GTX 260 Core 216 may look the same at first sight, but the cooling system conceals significant differences.
The PCB carries 14 memory chips indeed. All of them are installed on the face side of the PCB in order to simplify the wiring and the cooling system, but the power circuitry of the GeForce GTX 275 has been greatly revised. A 4-phase regulator was quite enough for powering the core of the GeForce GTX 260 Core 216, but the new design uses a 6-phase regulator. It is a reasonable solution considering the higher GPU frequency and the larger number of active subunits in it: 240 computing and 40 texture-mapping modules against 216 and 72, respectively.
The regulator is based on an ADP4100 controller manufactured by ON Semiconductor. We have not seen this chip before in our practice. It is unclear whether the option of software-based overclocking of the GeForce GTX 275 implemented in ATI and Nvidia cards using the Volterra VT1165 controller works here as well.
The memory chips are powered by uPI Semiconductor UP6161N and ENE Technology P2349WF chips, the latter being similar to and pin-compatible with the well-known Intersil 6549CBZ. External power is delivered through two 6-pin PCIe 1.0 connectors with a max load capacity of 75 watts each. The card does not allow for an installation of an 8-pin connector but we don’t think that G200b-based cards need it.