|PowerColor Radeon HD 6870 PCS+ Video Card|
|Reviews - Featured Reviews: Video Cards|
|Written by Bruce Normann|
|Monday, 10 January 2011|
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PowerColor PCS+ HD 6870 Detailed Features
The full PWM-based voltage regulator section that supplies power to the HD 6870 GPU is shown here. It is a 4-phase design that is controlled by a relatively new chip: the CHL8214 from CHiL Semiconductor Corporation. It is a dual-loop digital multi-phase buck controller specifically designed for GPU voltage regulation. Dynamic voltage control is programmable through the I2C protocol. CHil's first big design win in the graphics market was with a slightly meatier 6-phase chip in the GTX480 Fermi card, a power monster if there ever was one. The CHL8214 is a 4+1 design, but I don't see where the "extra" controller loop is used. It looks like the sense inputs for the "+1" controller are just tied to ground.
MSI is now supporting voltage control for the CHL8214 with their Afterburner software; it was only a matter of time before it was included. When the HD 6870 was first released, Alexey Nicolaychuk, the creator of RivaTuner, said "Development is in progress." It didn't take very long at all, less than a month for it to appear in a beta release. This is one of the advantages PowerColor got when it based their new design on the reference board; quick access to first-class monitoring and control software.
The VRM section also features another new chip in this application space; a DrMOS design from Texas Instruments that includes both the driver transistors and the High-Low MOSFET pair in one tightly integrated package. It's positioned right above the R22 chokes in the image above. It's a very small device, with markings of 59901M, and it's so new I can't find any specs for it. It has a bit of a reputation already though, as it is being blamed for the production delays of the AMD 6900 series cards. Apparently, it is in short supply for some unexpected reason, so AMD and their AIB partners had to do a fast workaround to get the Radeon HD6970 and HD6950 cards to market. It saves a huge amount of board space, which is critical in this unusual layout, where the designers have moved the VRM section to the flip side of where it's usually located; it is now situated between the GPU and the output connectors. A full complement of discrete MOSFETs and drivers for low side and high side circuits would not have fit in this area of the board.
This new DrMOS chip is considerably smaller than previous parts. It's only 6mm x 5mm, where some earlier DrMOS chips were 8mm x 8mm. It doesn't sound like such a big change, but the new part has less than half the surface area (30mm2 v. 64mm2). There is a single heatsink for the DrMOS chips, that's a custom design for this card. Look at the asymmetry of the layout, and you can see why this is not an off-the-shelf part. The foam heat transfer tape is thinner than most types I see lately, which improves its performance. By using a small, dedicated heat sink, the dimensional fit-up errors can be reduced, allowing a thinner tape to be used. The HD 6870 reference design has the DrMOS chips interfacing with the full-length carrier plate that covers the whole surface of the card. There is no (economical) way to make that large casting as precise as this small part.
The PC board had excellent solder quality and reasonably good precision on component placement, as can be seen below. This is the area on the back side of the board, directly below the GPU, and it's one of the most crowded sections of any graphics card. On my LCD screen, this image is magnified 20X, compared to what the naked eye sees. The small SMD capacitors located side-by-side in this view are placed on 1mm centers. This is one of the most critical sections of the PCB for build quality, as variations in stray capacitance here could impact the performance of the GPU, and certainly its overclocking ability.
This board was above average for cleanliness, compared to some of the samples I've looked at recently. There were some traces of residue across different sections of the board, but they weren't excessive. Once you start looking at macro photographs like this, there's no place for any manufacturing shortcuts to hide. All manufacturers are under intense pressure to minimize the environmental impact of their operations, and cleaning processes have historically produced some of the most prolific and toxic industrial waste streams. The combination of eco-friendly solvents, lead-free solder, and smaller SMD components have made cleaning of electronic assemblies much more difficult than it used to be.
The memory choice for the PowerColor PCS+ HD 6870 1GB GDDR5 is consistent with the AMD reference designs. The basic Radeon HD 6870 specs only require 1050 MHz chips for the memory, but these Hynix H5GQ1H24AFR-T2C GDDR5 parts are designed for up to 1250 MHz. The 1250 MHz Samsung chips on the HD 5xxx series of Radeon cards have been mediocre overclockers; we'll have to see if these Hynix parts are a little more willing to exceed their ratings.
Let's dig a little deeper inside the Features and Specifications of the Radeon HD 6870 GPU, before we get into full-on test mode...