Pros and Cons of Digital PWM?

[OSKAR_WU]

When the cpu load changes , no matter how fast the VRM can respond , there is always a very short period you need to use the Choke and Capacitor to maintain the voltage stable ... If we can design unlimited capacitor on the board , we can remove the droop design when the capacitor can handle all these transient state , but that's not possible ...

[hipro5]

When the cpu load changes , no matter how fast the VRM can respond , there is always a very short period you need to use the Choke and Capacitor to maintain the voltage stable ... If we can design unlimited capacitor on the board , we can remove the droop design when the capacitor can handle all these transient state , but that's not possible ...

From the schematics you have uploaded, users can see how the power circuit responds from heavy load to light load (idle) and visa-versa.....

a. Digital OR traditional VRM with ALL the Mos-Fets in ONE LINE (straight) and cooling them with ONLY ONE heatsink, IS WRONG.....
Why?......EVEN if a user place the DEFAULT Intel heatsink onto the CPU, the motherboard is NEVER going to be in a "straight line" - take a look at it from it's side - .....
By this, the CENTRED Mos-Fets are getting WAY hotter than the sided ones....
Imagine now that a user buys another CPU heatsink and he starts to squeeze it much more.....
BIG mistake putting ALL Mos-Fets in one line with ONE heatsink on them.....
Do you want to talk now about the enthousiasts with the cascades/LN2s?....You get an "S" shape motherboard.....

I'm NOT talking about DFI here......I'm talking about ALL.....


b. When using a Digital VRM Mos-IC-Fet, you encode two problems:
1. TOO tiny surface to cool down with a heatsink and
2. in case that some user wants to takes off it's heatsink and place another one on them, they are TOO delicate and they break VERY EASY....(Even a corner of them if it breaks you're s(crewed....


c. NO MATTER how high switching frequency the Digital VRM you make to work for efficiency/etc., you CAN'T "filter" the "Voltage spikes" from idle to full load of a CPU.....
By NOT using electrolytic capacitors ALSO ADDED on their output circuit so to "catch" (filter) better those voltage spikes and "walking" on the reference design of Voltera (for example), you're doing NOTHING....


My thoughts:

a. If you want to use Digital it's OK BUT place those Mos-IC-Fet by TWO (and only OR by 4 in a square) with a quite big heatsink on them (forget heatpipes and crap like this)....
b. ADD some elecrolytic capacitors on their outputs...(SMDs like ASUS uses in some of their designs "catches" faster those voltage spikes - Vdroop of ASUS is another thing though and it has nothing to do with them - )
c. Use AT LEAST 8 Digitals so by placing them in square, you will need only two quite big heatsinks which MUST NOT TOUCH each other with heatpipe or anything else in case the motherboard gets stretched by the CPU heatsink or so....
d. DON'T use the "lined" chokes for the digital......when a user screws his mobo with the heatsink/LN2 pot/cascade, some of them break their ceramic cover and they become useless.....

.

[Pete]

True bloody facts

Very very nicely put there.

Now why are all the MOBO MFGS focusing on having people like Oska oc'ing the willys off the bord when what they need in the first place is someone like Hipro that knows the facts both at the engiering aspect but end user.

Hipro maybe you should get some mobo made of your own desgin, id pay for it

[hipro5]

Very nice read, as always, George!

Very very nicely put there.

Now why are all the MOBO MFGS focusing on having people like Oska oc'ing the willys off the bord when what they need in the first place is someone like Hipro that knows the facts both at the engiering aspect but end user.

Hipro maybe you should get some mobo made of your own desgin, id pay for it

Thanks guys, but that's just facts....

Oskar is a hell of technician you guys.....DON'T underestimate of him...

Have you guys ever thought that he's NOT alone?...He just CAN'T do whatever he wishes.....He's an employ.....So in some cases/designs sometimes "other people" may tell him what to put on or off of a mobo.....what parts for example.....cheaper, etc......

IF "they" leave him alone, I bet he could do miracles...

Another thing I whould also like to add :
Manufacturers GET R.F. technicians TOO......We are NOT anymore at 33MHz....We are WAY HIGHER than that.....
This is going (pointing) to anyone who can understand of what I'm talking about....

[dinos22]

hipro it's simple

make a little pot for the mosfets and stick some dice on it during the runs

[hipro5]

hipro it's simple

make a little pot for the mosfets and stick some dice on it during the runs

NOT that simple.....It won't "touch" ALL of them when mobo gets squeezed and changed it's "lined shape"...

Take a look at the below photo and HOW a mobo could become to fully understand of what I'm talking about.....



Now put me a "straight heatsink" on those (let's suppose) Digitals to cool them down.....


EDIT: BUT I know why you said that!.....You want that OVP mod of the NVIDIA....

.

[dinos22]

lol biatch

nah i'm serious

also in terms of bending there is a solution for that too

i could quote some nice pics MM posted a long time ago of his wooden board and rubber standoffs but CFB looking it up

you get the idea though

let me recap then ...... wooden/metal solid board for benching with good wide and fairly short rubber standoffs and DICE cooling on PWM and you are good to go....you will have no heat in that area of mobo and mobo should be dead straight mounted on the board..............i see no reason why it would get bend that badly

[Ace-a-Rue]

Thanks guys, but that's just facts....

Oskar is a hell of technician you guys.....DON'T underestimate of him...

Have you guys ever thought that he's NOT alone?...He just CAN'T do whatever he wishes.....He's an employ.....So in some cases/designs sometimes "other people" may tell him what to put on or off of a mobo.....what parts for example.....cheaper, etc......

IF "they" leave him alone, I bet he could do miracles...

Another thing I whould also like to add :
Manufacturers GET R.F. technicians TOO......We are NOT anymore at 33MHz....We are WAY HIGHER than that.....
This is going (pointing) to anyone who can understand of what I'm talking about....

that last para flew over my head but those para's above that last read so TRUE to my eyes and ears!

[MrToad]

It has been mentioned before in the thread, but I also find digital PWMs a PITA from a mechanical point of view.

With my (defunct) IN9 32X I found myself in a catch 22 situation, which I was never able to overcome, and ultimately led to irreversible damage (I crushed the ceramic encapsulation).

With the default setup, and no OC, chips would shoot to what I understood as unreasonable 80-90 C.

Same setup, mild OC (X6800 @ 3.33 Ghz), they would shoot to 99-108 C under load.

Changing the thermal pad for a different type (the thick light blue one you often find in laptop GPU/VRegs) had no measurable impact on temperatures.

Liquid TIM was a no-go with the default HS, as it had (wisely enough) "legs", which left a gap enough to run freely a green rizla between the HS and the chips. Filling such void with Ceramique or MX-1 was impractical.

I looked at the possibility of making some sort of custom HS, but I didn't have at the time tools or a place to do so.

I finally acquired a water block from mips.de, and decided to give it a try. The problem I faced was... torque.

Too much and the PCB would warp leaving the centre chip with no contact whatsoever, and risk crushing the most external ones.

Not enough and the block would tilt due to the traction/torsion of the tubing.

The difference between "not-enough" and "too-much" was so little that achieving a good mount became a job for a 70 yr old Swiss clock maker.

In the end, my patience run out, and with it my pulse. I heard a sound like someone stepping on wet sand, and there went my MB.

In retrospective, even having used a back plate wouldn't have helped that much. Being the ceramic encapsulation so brittle, and with such tiny surface area, I doubt I would have managed to apply enough torque to leave the block sitting completely parallel to the surface without the same dreadful consequences.

[dinos22]

does DFI get THAT hot as well