An Introduction to Accurate Voltage Measurements - Everlasting Vdroop Dilemma

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Everlasting Vdroop Dilemma

Another problem that can occur is vdroop. What exactly does a “vdroop” mean? We call vdroop the stage when the Vcore (VCC) drops on high load to a lower voltage, therefore feeding the processor a lower amount of voltage. You might have 1.40v in BIOS, out of which 1.38v is real-time when your CPU is idling, but as soon as it gets loaded with hard work it might drop to 1.34v or even lower, who knows?

Why does this happen? Processors are apparently designed to work stable, allowing a particular amount of vdroop. Vdroop is there to prolong the life of the motherboard’s VRM circuitry (voltage regulator module), those MOSFETs, their drivers, inductors and capacitors that assist your multi-phase PWMIC (Pulse Width Modulation IC).

Check out the attached picture below. It’s half of the VRM area on a Gigabyte GA-965P-DQ6 motherboard. What I mean by half is that you can only see one side of the whole VRM circuitry from this angle, hence half of it. There’s another identical portion of it on the other side of the CPU socket.

(Gigabyte GA-965P-DQ6 — photo courtesy of VR-Zone.)

Paying close attention to the above picture you notice 2x6 MOSFETs (in pairs), 6 power cube-like inductors and 6 polymer electrolytic capacitors (low ESR). Since this picture is ½ of the VRM, there’s a grand total of 2x12 MOSFETs, 12 inductors and 12 caps. As a result, the Gigabyte GA-965P-DQ6 has a robust 12 Phase Power VRM.

Adding a “slight” droop is always a cost-effective solution for motherboard manufacturers. Basically it maintains a relatively smooth output voltage by reducing the intensity of the spikes between idle and high load; the droop is well controlled and deterministic. This is crucial because as CPUs get more powerful they require a steadier source of power, and need to not cross (often) the limits of VCCmax and VCCmin.

Contrary to popular belief, a higher-phase regular is not always better than a lower-phase one. It’s all about quality — how well the circuitry is tuned, designed, and implemented. Unfortunately, more often than not, motherboard manufacturers opt for the easiest solution, that is, going for an 8-phase+ regulator even though a well-tuned lesser-phase one could be enough. It’s easier to implement (no optimization required, less manufacturing cost), and it’s something that “looks nice” on marketing ads.

Gigabyte’s latest motherboards often choose the 12-phase power route but I am by no means saying that their design performs poorly. I was just hinting at the fact that in electronics, “more” isn’t always “better.” The quality of the components matters the most!

Next: Measuring PSU Rails >>
 

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