i5-750 and load line calibration

[mark_j]

I have an i5-750 running on an MSI P55-GD65 mobo. Corsair 750w ps.

I set the vcore to 1.270 and it idles at 1.264 (CPUz) and P95 loads at 1.192 (serious vdroop going on here). It will OC to 3500MHz (167x21) at this setting but will fail P95 after about an hour at 3600MHz (172x21).

If I change the Load Line Calibration setting in BIOS and set the vcore to 1.213, the vcore reported by CPUz will actually rise at both idle and load (1.232 under load). It is stable at 3600MHz at this setting and I did not try to push it higher.

I have read a few articles and forum posts regarding load line calibration at different places on the internet. Some OC guilds tell you to use it because it allows higher & more stable overclocks (my experience so far agrees with this) but some articles say that vdroop is part of Intel's spec for the processor and not allowing it will risk damage.

Which is it? Neither? Both?

Thanks for any advice.

Mark

 

[Markfw]

IMO, I always use it for overclocking, but then again, my boxes are also always under load.

 

[aigomorla]

Load line calibration attemps to counter vdroop by raising the vcore on your cpu.

However on a normal load up processor, you get a voltage spike, and with load line calibration that spike can get higher.

My general take on it is, i recomend it for people who are after lower voltage ocing.
Like sub 1.4vcore which where you fall under for your exact reasons.
The vdroop will play havok with your OC when your at lower voltages.

However when going at higher voltages its recomended that u dont leave this on because of the overshoot potential.

Seeing how your playing with Tiny tiny voltages, leave it on.
I dont see any harm to your chip with it on at those voltages.

 

[mark_j]

Wow..two quick answers from two moderators. Thanks for the advice. And yes, I do not plan to go over 1.25v in bios with LLC enabled.

 

[JAG87]

I like to answer these kind of questions.

LLC is neither good or bad. It was created in an effort to achieve higher load voltage without having to increase VID and subsequently have higher idle voltage. Vdroop was implemented because whenever there is a major change in amp draw from the load, the voltage regulators lose stability and briefly (<50ms duration) overshoot/undershoot the voltage to conpensate. This can be compared to turning on a heavy appliance and seeing the lights in your room dim. That's what happens when the CPU goes under load. When the CPU comes out of load the exact opposite happens. When this overshoot happens, the voltage might exceed the maximum safe voltage.

Not all motherboards have the same power delivery regulators. Some will overshoot/undershoot more while some less. It all depends on the quality and rating of the components. Without getting too technical you can find out what kind of power delivery your board sports by just looking at the amount of vdroop implemented. If under heavy overclock the voltage droops by 0.05v, that means your under/overshoots are about 0.05v. That means if you use LLC and set the voltage to 1.3v, you can expect your cpu to get hit briefly with 1.35v when coming out of load. Poor boards will droop up to 0.1v. That means if you use LLC with 1.3v to achieve stability, your CPU is getting hit with 1.4v coming out of load. If you allowed droop in this situation, 1.3v would droop to 1.2v and coming out of load the spike would not exceed the VID you set in the bios.

The conclusion is if your board has little vdroop, hence good voltage regulation, you can use LLC and be confident that your overshoot spike will be minimal. If however your board has poor vreg and lots of vdroop, you are better off without it. Also because just like with a VID of 1.3v the voltage briefly overshoots to 1.4v, it also briefly undershoots to 1.2v when entering load, so having 1.3v set in the bios could still give you a nice BSOD as soon as you enter load.

 

[The Sauce]

I look at it this way. Your CPU will spend the most time idling and very little time under full load. Hence, I would rather have a lower voltage at idle for the majority of my CPU's life, and a higher voltage (even with theoretical brief spikes) during less common load conditions, when instability and errors are likely to occur. I have been using LLC on my 750 since I first got it at 4200 MHz with VID @ 1.35. My CPU has not burst into flames yet.

 

[mark_j]

Ok, thanks to everyone's advice, I set vcore to 1.195 in bios with LLC. 1.224 in CPUz when running P95 at 3600MHz. Temps are maxing out at 62c on the hottest core. I even loaded and unloaded the processor repeatedly to try and cause instability but it seems solid.

I'm happy. Cheers.

 

[n7]

I've used it on all my mobos that have had it.

It's likely more dangerous if used on crap mobos that have poor power delivery.

It's not really an issue with a good mobo & reasonable voltages though, IMO.

I prefer having lower idle voltage w/ a bit higher vcore under load than much higher under idle & lower under load, as has already been mentioned.

 

[MrK6]

Of note with the i5 750, I've found it's a lot easier to stabilize the chip at lower voltages with all power saving settings on and LLC off. For some reason I could never get it to play nice with LLC on, but voltage is cut to something <0.9V on idle anyway, so having a high idle voltage with power savings on really doesn't matter much.