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EMC2 · 03-12-2002, 04:55 PM

Okay, here is how the circuit works and what the mods actually do

Pin 7 is the feedback resistor to the error amplifier. The ratio of it's resistance to the resistance of Rcomp that runs between pins 7 and 6 set the gain of the error amplifier (basic op amp operation).

The voltage level seen at pin 7 is amplified by the error amp and the controller IC adjusts the output voltage accordingly. The lower the voltage seen at pin 7, the higher the IC will drive the Vcore voltage level.

When you put a resistor between pin 7 and ground, you are decreasing the voltage level seen by the error amplifier, thus increasing the VCore voltage.

If that were the only part of the control loop, everything would be fine and dandy. But it isn't. The HIP6301 also has a VCore sense input for detecting under/over voltage conditions. This is pin 10. If the voltage level here gets either too high or too low (greater than 15% difference from the voltage programmed by the VID pins), the controller will turn off the VCore circuit, shutting down the system. To stay within this 15%, the max you could program the Vcore for is a 2.1V output when VCore is set to 1.85V in the BIOS.

Going above 2.1V for Vcore is where the 2nd resistor in the Shuttle mod you reference comes into play. By putting a resistor between pin 10 and ground, you also decrease slightly the voltage seen at the Vsense node. This prevents the controller from shutting down when you crank up the Vcore signal level.

Summary, depending upon how high you intend to crank the Vcore voltage, you could get away with the single resistor on the Vfeedback pin (7). However, if you go too high with Vcore (above ~2.1V) and start getting shutdowns, you will have to add the 2nd resistor that connects to the Vsense pin (10).

In regards to your question about the potentiometer your using - are you using the center tap and one of the two end taps?

A potentiometer has 3 connections, there is a connection to each end of the resistor and then the 3rd connection is hooked to the wiper arm that moves between the two ends of the resistor. If you accidently hook up to the two end connections, you will always read the value of the resistor, no matter how much you turn the dial (in your case, 50Kohms).

You should hook your jumpers up and measure BEFORE you connect to the circuit and make SURE of two things. 1) one connection is to the center tap (verified by watching the resistance change between your leads when you turn the dial. 2) that the initial resistance you have it set to is at least 45Kohms between your leads. Again, both of these checks should be made before you hook your clips up to your motherboard.

<edit> One other thing of importance - you need to keep the length of the leads between the clip going to the IC legs and the potentiometer as short as possible. Ideally you will have only enough wire coming out of the clip to solder the potentiometer leg to. This is because of the sensitivity of the feedback circuit. Remember, this is going into a high gain error amplifier. If you leave the leads long and start picking up a lot of noise, your Vcore will fluctuate

03-12-2002, 04:55 PM	#5
EMC2 Cooling Savant Join Date: Feb 2002 Location: Dark Side of the Moon Posts: 365	Okay, here is how the circuit works and what the mods actually do Pin 7 is the feedback resistor to the error amplifier. The ratio of it's resistance to the resistance of Rcomp that runs between pins 7 and 6 set the gain of the error amplifier (basic op amp operation). The voltage level seen at pin 7 is amplified by the error amp and the controller IC adjusts the output voltage accordingly. The lower the voltage seen at pin 7, the higher the IC will drive the Vcore voltage level. When you put a resistor between pin 7 and ground, you are decreasing the voltage level seen by the error amplifier, thus increasing the VCore voltage. If that were the only part of the control loop, everything would be fine and dandy. But it isn't. The HIP6301 also has a VCore sense input for detecting under/over voltage conditions. This is pin 10. If the voltage level here gets either too high or too low (greater than 15% difference from the voltage programmed by the VID pins), the controller will turn off the VCore circuit, shutting down the system. To stay within this 15%, the max you could program the Vcore for is a 2.1V output when VCore is set to 1.85V in the BIOS. Going above 2.1V for Vcore is where the 2nd resistor in the Shuttle mod you reference comes into play. By putting a resistor between pin 10 and ground, you also decrease slightly the voltage seen at the Vsense node. This prevents the controller from shutting down when you crank up the Vcore signal level. Summary, depending upon how high you intend to crank the Vcore voltage, you could get away with the single resistor on the Vfeedback pin (7). However, if you go too high with Vcore (above ~2.1V) and start getting shutdowns, you will have to add the 2nd resistor that connects to the Vsense pin (10). In regards to your question about the potentiometer your using - are you using the center tap and one of the two end taps? A potentiometer has 3 connections, there is a connection to each end of the resistor and then the 3rd connection is hooked to the wiper arm that moves between the two ends of the resistor. If you accidently hook up to the two end connections, you will always read the value of the resistor, no matter how much you turn the dial (in your case, 50Kohms). You should hook your jumpers up and measure BEFORE you connect to the circuit and make SURE of two things. 1) one connection is to the center tap (verified by watching the resistance change between your leads when you turn the dial. 2) that the initial resistance you have it set to is at least 45Kohms between your leads. Again, both of these checks should be made before you hook your clips up to your motherboard. <edit> One other thing of importance - you need to keep the length of the leads between the clip going to the IC legs and the potentiometer as short as possible. Ideally you will have only enough wire coming out of the clip to solder the potentiometer leg to. This is because of the sensitivity of the feedback circuit. Remember, this is going into a high gain error amplifier. If you leave the leads long and start picking up a lot of noise, your Vcore will fluctuate Last edited by EMC2; 03-12-2002 at 05:03 PM.