X-bit labs

First in DirectX 10.1: ATI Radeon HD 3850/3870 (page 12)

Category: Video

by Alexey Stepin , Yaroslav Lyssenko, Anton Shilov

[ 01/25/2008 | 10:31 AM ]

Cooling System

The cooler of the ATI Radeon HD 3850 has a single-slot form-factor. That’s why it is more sophisticated than the cooler of the Radeon HD 3870.

A dual-slot form-factor doesn’t impose strict limitations on the type of the fan or the size of the heatsink and the developer can vary both to achieve the optimal combination of thermal and noise characteristics. It is not so with single-slot coolers: the developer has to resort to various tricks and compromises to remain within the limits of the form-factor while achieving the desired cooling efficiency. Sometimes silence has to be sacrificed even. An example of such a compromise is the reference cooler installed on the GeForce 8800 GT. The new cooler of the Radeon HD 3850 resembles it with its design and component layout.

Don’t be confused with the color of the metal the base of the cooler is molded from: it is not copper but aluminum, which we checked out by scratching the base. A flat heat pipe is pressed into the groove at the top to distribute the heat in the heatsink, and there is a copper piece where the cooler touches the GPU. Consisting of aluminum plates, the heatsink has a much larger total area than the heatsink of the GeForce 8800 GT’s cooler and is installed upright rather than at an angle. The air flow is driven away from the mounting bracket by means of special grooves in the cooler casing.

We don’t think it’s an ideal component layout, though. We guess the fan should have been instead placed near the DVI-I connectors, changing the direction of air flow to the opposite. In this case the hot air from the main heatsink could additionally cool the load-bearing components of the power circuit because the base is shaped like an additional needle-like heatsink there. Well, at an expected power draw of 50-60W, this cooler should cope with cooling the Radeon HD 3850 just fine. We can recall Nvidia who dared to use a similar component layout with a smaller heatsink to cool a graphics card with a power draw of 80W – the company and the users are still suffering from that attempt.

The cooler is equipped with a flat centrifugal fan of a rather small diameter with a 4-pin connection, which indicates PWM-based regulation of speed. Its noise parameters are questionable, but we expect it to rotate at low speed most of them due to the lower heat dissipation of the RV670 chip clocked at 670MHz and to the rather large heatsink.

There are the same thermal interfaces where the cooler contacts the GPU, memory chips and load transistors of the power circuit as in the cooling system of the Radeon HD 3870: dark-gray thermal grease for the GPU and elastic yellow thermal pads for the rest of the chips. Besides the four poles with spring-loaded screws and a metallic back-plate the cooler is fastened to the PCB with six additional screws, four near the memory chips and two near the MOSFETs. This prevents the cooler from misaligning and damaging the graphics core.

The cooler installed on the Radeon HD 3850 looks good overall. Perhaps it is not ideal (we do think that the position of the fan and the direction of its air flow is not quite correct), but this shouldn’t be a problem considering the lower heat dissipation of the chip in comparison with the Radeon HD 3870 especially as this cooler employs a more advanced heatsink that in the GeForce 8800 GT’s cooler.