Radeon X800 Non-Pro/X800 XL/X850 Voltmods

Author: Urlyin
Date: 2005-02-11 12:48:55


This article is based on the previous voltmod article for the Radeon X800 Pro, X800 Pro VIVO, X800XT and X800XT PE AGP line and has been adapted to apply to the Radeon X800 Non-Pro, X800 XL and X850 PCI-Express line using PCB #A474.

As always, the familar warning of "This will void the warranty" and "We take no responsibility of any kind should you damage your video card" applies before we start. Remember to take your time and don't over do it. You should seriously consider replacing the stock HSF if you plan to crank high on the overclock . Check out our GPU Heat Sink Fan Reviews here.

You should have at least tested your video card for a week under benchmarking and gaming before beginning the vmods to rule out issues prior to starting your vmods. Also, should you have any questions or information you wish to share, please post them here.


The chips that we will be working with are the same in both series, just in slightly different locations. With ATI's introduction of these cards they have new GPU cores as well.

Card NameGPU Core
X800 XLR430

The ATI's official X800 GPU temp specs remain the same for these cores:
Thermal Parameter Valuetemperature
Maximum recommended ASIC case (or center of die backside for flip chip)105°C
Absolute maximum rated junction temperature: TJmax125°C
Minimum ambient operating temperature0°C
The chips will be working with:
VGPU: Fairchild FAN5240MTC, Datasheet
VDD & VDDQ: Intersil ISL6522CB, Datasheet

The FAN5240MTC that we will be doing our VGPU voltmod on also has another use. Interesting info from Fairchilds product folder:
General description

The FAN5240 is a single output 2-Phase synchronous buck controller to power AMD's mobile CPU core. The FAN5240 includes a 5-bit digital-to-analog converter (DAC) that adjusts the core PWM output voltage from 0.925VDC to 2.0VDC, which may be changed during operation. Special measures are taken to allow the output to transition with controlled slew rate to comply with AMD's Power Now™ technology. The FAN5240 includes a precision reference, and a proprietary architecture with integrated compensation providing excellent static and dynamic core voltage regulation. The regulator includes special circuitry which balances the 2 phase currents for maximum efficiency.

Max. safe voltages

Stock:1.31V - 1.41V
Air cooling:~1.45V
Water cooling:~1.7V
Phase change:~1.85V

Stock:1.95V - 2.05V
Active + Passive cooling:2.45V

Stock:2.04V - 2.10V

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