Improve VDIMM regulator

[Calchaqui]

Hi guys, it's an old mobo with 4 sdram dimm (3.3v), to run it stable with all-4-dimms-filled i need @3.7v . Mobo takes input voltage from 5v rail to give 3.3v, next to dimms there's 1 little unisem 1010 and 3x1000uf, i hacked the voltage resistor and I got 3.6-3.7v output, the problem is that little regulator is rated only 1amp and it gets ULTRA HOT, how can i improve it?
This's the main spec
http://html.alldatasheet.com/html-pd.../1/US1010.html
Can i solder another one in parallel? :S:S (sorry if im saying something stupid)
I have lotta dead mobos, which STRONGER part could replace it?

[mariushm]

Re: Improve VDIMM regulator

That is a linear regulator, it generates lower voltage from higher voltage.

It has a guaranteed voltage drop of less than 1.3v, so in order to get any voltage stable there has to be at least 1.3v difference between input voltage and output.

So with 5v input, you shouldn't set the resistors to output more than 3.7v

Anyway, the difference in voltage gets wasted as heat, so you have about 1.3 watts of power dissipated into the board as heat. Any other linear regulator in the same format (package type) will be just as hot, because the pcb has to act like a heatsink to take the heat off the chip.

Your best bet would be to get a linear regulator in another package that can dissipate heat better, like dpak /to-263 or to-220 and put that on a heatsink - you won't be able to solder those onto the motherboard as they're too big but you would be able to glue it down somewhere.

As for what to use, first thing that came in mind to me was LM1085 (3A ldo with 1.3v max drop, just like what you have) or LM1084 (same but 5a max)

http://www.digikey.com/product-detai...NOPB-ND/363565

http://www.digikey.com/product-detai...NOPB-ND/363561

but they NEED a heatsink to work at more than 200-300mA continuously. Can't just solder directly on the pcb instead of old one.


Pretty much anything in that package (format) will be just as hot, because you're dissipating 5v-3.7v = 1.3v x 1A

[Calchaqui]

Re: Improve VDIMM regulator

Thank u very much Mariushm, what do you think is the consumption of 4x512mb (16chipsx4) sdramm dimms at 3.3v?
I'm pretty confused about current here, in another revition of the mobo, there's a 28N03L mosfet to do the job which is rated at 30AMP, and here we are talking about 1AMP? im confused

[tom66]

Re: Improve VDIMM regulator

Doesn't matter how many amps the regulator/MOSFET is rated for -- you still have to obey the inevitable laws of thermodynamics. Things dissipating energy get hot. Hot things can fail if they get too hot, so you must keep them cool.

[Calchaqui]

Re: Improve VDIMM regulator

Doesn't matter how many amps the regulator/MOSFET is rated for -- you still have to obey the inevitable laws of thermodynamics. Things dissipating energy get hot. Hot things can fail if they get too hot, so you must keep them cool.

Yeah I know that, but each 512mb sticks consumes about 5w, so we've got at least 20w consumption, which's about 6AMP @ 3.3v, this little regulator says 1A MAX output, something is outta specs? am i wrong tom66? thnk u

[budm]

Re: Improve VDIMM regulator

Are you sure that one stick of 512mb SDRAM uses 5 Watts of power?

http://www.micron.com/products/support/power-calc

[Calchaqui]

Re: Improve VDIMM regulator

Are you sure that one stick of 512mb SDRAM uses 5 Watts of power?

http://www.micron.com/products/support/power-calc

That's what I've read in tomshardware forum, thnk u budm for that link!

[tmiha71]

Re: Improve VDIMM regulator

From sheets (for 128 Mb -Mbyte? module) :
System is operating at 133 MHz at VCC = 3,3V. Read bandwidth is 53,2MB/s with write bandwidth of 19,95 MB/s. The data bus is idle 45% of the time.
consumption is ~550 mWat. This speeds are FUNNY (and consumption depends on speed)...
If it's 128 Mbyte module, to get 512 Mbyte module we need to multiply with 4...
So guessed consumption per module is ~2W, and for four modules NOT just multiply with 4, but ONLY background power (and activate power ???)...
What we can say, max consumption, for circumstances above, with all 4 DIMMs populated, is LESS than 8W - what translates to 3 A.

Note - if mobo does not have at least 3 capacitors (8 mm dia) for DIMMs -> can lead to severe problem...
Note - your board is designed (LDO specs) for ONE 512MB stick (maybe two, if you're lucky)...
Stronger LDO would help, but heating is problem, and ripple which is generated by stronger LDO should be minimized...

[Calchaqui]

Re: Improve VDIMM regulator

Yep, they've made a very cheapo dimm VRM. Sorry, this's very off-topic, what the red-circle VRM regulates? it takes drain from 5v rail and source is 3.3v, but it is far from NB, DIMMS , and close to SB (allofthem 3.3v), i've never seen a dedicated vrm for SB. What do u think is it for?

[ben7]

Re: Improve VDIMM regulator

There are chips you can use to build a more effiecient switching regulator, or you can buy a pre made one made by TDK, and a few other companies.

[tmiha71]

Re: Improve VDIMM regulator

Yep, they've made a very cheapo dimm VRM.

Or they had better (more accurate) data, or went on lower edge -> to disable overclocking, or 512 MB sticks were not available at that time...

Note:
Increasing voltage, to DIMMs is cheating, usually indicates dirty voltage (which can be result of badly specified capacitors, or too low count of electrolyte capacitors, or some other design flaw...)

3DMark (any) runs with your mod ?