Originally Posted by HiroPro
I dunno man... the language is so bad I thought the guy was claiming to have fixed an "I/V" stage or something...
Yeah the VRM section of that board is very cheaply designed and wasteful. I love the 20 phase PWM Intersil VRD12 (only Intel approved digital PWM) on my P67A-UD5-B3. Asus has a digital PWM VRM section but it doesn't use Intel approved PWM!
Actually Intersil PWM on your board is analog mix-signaled.
Analog PWM uses voltage/current control feedback, it does this by taking the output of difference from a current sensing resistor(current mode), or the vout(voltage mode), and amplifies and compares against a reference voltage(what the voltage should be), then if the output is low it changes the duty cycle accordingly to increase the output, or is reduces it if the output is too high, and it does this thousands of times per second. Its basically the 100% hardware method with the amplifier and comparator. its very fast, but it has a downside, its not very accurate to keep increase the output until its too high and decreasing until its too low and then increase or decrease again.
Digital PWMs in a sense compare the output to the reference through a PID algorithm in a digital way through firmware, but to get the output into digital 1s and 0s they have to use an analog to digital converter, which is a huge source of delay. The upside is that it will adjust the duty cycle just enough to make the output equal to reference, so if wont wait until the output is higher than the reference to change the duty cycle.
Both are precise, but the digital is more accurate. But precision and accuracy are only one part of the equation, transient response and how a PWM is able to handle load changes, as well as other technologies like phase alignment where every phase is turned on at the same time can greatly impact a VRM's performance. When you have factors that control the transient response like output capacitor ESR, switching frequency, and MOSFET parasitics.
Transient responce might be actually the most imporatnt factor, as it ussualy intertwines with ripple. Switching frequency is one of those numbers usually thrown around. lets take a LGA1155 example.
The P8p67 series has PWM frequency control, and many know you need to set to 350khz to OC higher than certain values.
All GIGABYTE LGA155 boards at this point switch at 264khz or below wether by restriction like with the 20 or 24 phases, or by choice with the 8-12 phase designs, and the truth is even with one of the lowest switching frequencies they still OC as high as the rest, and they get Intel VRD12 certifications easily.
part of it is because GIGABYTE boards use much less bulk output capacitance to get around ESR, and the way they do this is because of some active phase positioning tech from intesil PWM which allows the increase number of phases to interleave, thus multiplying the output ripple current, and reducing the need for more output capacitance to reduce ripple.
Go look up ISL6366 which is the top of like VRD 12 Intersil PWM, all these techs are explained in the datasheet,as well as the graph in there that shows interleaving and its affects on ripple.
Anyways Most every other company other than MSI, and some EVGA boards use Chil DIGITAL PWMs, which actually now DO HAVE VRD12 certification. They received it after release, but that is because they can flash the firmware of the PWM through a simple BIOS update.
Bottom line is that Digital and analog are marketing terms, they do have some truth as the feedback control loops are different as i stated, but other than that they are very similar. The both has VRD12 certification now, but Intersil did have it first. of course there is one other company uPI Semiconductor, and they make PWMs on the EVGA P67 FTW which has a ok VRM( works at 264khz as well, but not as good performance as the intersil, as it takes more voltage to get same OC by a lot i hear), EVGA switched to Chil now for Z68. MSI also uses uPI, and their switching frequency is high, that is why their phase count is low.
higher switching frequency = higher heat and lower efficiency per phase, add more phases at high switching frequency and your VRm gets wayy to hott, example is Volterra Z58 Classified VRM, actually prob one of the best VRMs on a motherboard, just runs way too hot.
Higher witching frequency also equals less ripple as the changes in load are dealt with quicker, and thus better transient response.
Another example is X58 OC board from GB, upto 1mhz switching frequency but only 12 phases.
the X58A-UD9 has dual PWMs to maintain a 500khz switching frequency across 24 phases which is very impressive, but every other GB X58 board is 264khz.
The GB UD9 and OC board have the best GB VRMs ever made, the UD7s of the X58 and Z68/P67 lines do not have the same 24 phase design as the UD9, they are missing a whole other PWM hahahaha.Edited by Sin0822 - 8/25/11 at 12:15pm