Teardown of 1V 800A mainframe PSU - Page 1
Forum section: electronics / general

author: tszaboo
author_rank: Super Contributor
timestamp: June 16, 2016, 11:11:41 am
content: Yeah, 800 amps baby.I liked working with high currents (record was up to 4000A).But someone at IBM has to learn the term POL.

author: TiN
author_rank: Super Contributor
timestamp: June 17, 2016, 12:16:35 pm
content: POL or not, it does not change design much, as you still have to give those 800W to ASICs in the end. Even if POL supply right the CPU package/si (google FIVR intel 4th and 5th gen Core CPUs) there are losses on conversion of higher VCC to internal output rails.

author: uncle_bob
author_rank: Unknown
timestamp: June 17, 2016, 01:07:44 pm
content: HiThere's a lot of money in 800A of connectors and board copper issues (added layers for planes etc). That cost scales down more than a little as you up the voltage and drop the current. Silicon just keeps getting cheaper so the cost trade off moves more towards the onboard regulators every year. None of that even starts to get into the advantages of being able to control the voltage on each of the ICs *much* more accurately. That lets you fine tune speeds and get more bang for the (big) bucks you put into those ASIC's. If the regulators are running above 90% efficiency, that's down in the round off error on a big system.Bob

author: tszaboo
author_rank: Super Contributor
timestamp: June 17, 2016, 02:15:14 pm
content: Quote from: uncle_bob on June 17, 2016, 01:07:44 pmI've used 50A POLs. They are tiny, requireing something like 12 sqr cm. Double that for the decoupling. The issue with the high current is A) you need a lot of copper for the voltage drop B) You need a lot of copper for the dissipation B) You need a lot of copper for the heat. A 12-1V 50-100A converter happily lives right next to the ASIC/CPU, because the current path is wide, and short, not the other way around. Carrying the same amount of power at 12V, and have the same dissipation requires less than 1% of the copper.You need to assume that no single IC will eat that 800A. Which I think is safe to assume. I never seen more than 150ish W at 1.2ish Volt. Maybe it was powering a Monster 800A IC of water cooled radio frequency death ray amplifier.

author: uncle_bob
author_rank: Unknown
timestamp: June 17, 2016, 02:34:21 pm
content: Quote from: NANDBlog on June 17, 2016, 02:15:14 pmHiThe final gotcha on your 800A death ray ASIC is ... how do you get 800A into the chip? Your super duper ultimate ASIC today is likely done as a BGA of some sort. It *might* be on 0.5 mm spacing. To truly qualify for "super status" it could be a bit tighter than that. At one or two amps per pad, you are using a *lot* of pads for power and ground at 800A.Yes, even at a core voltage of 0.5V (not quite there yet), 800A will dump 400W into your die. Unless it is the size of a dinner plate, you will need liquid nitrogen to cool it. Of course if it's 8" square, that would give you room for all those power padsBob

author: uncle_bob
author_rank: Unknown
timestamp: June 17, 2016, 03:18:04 pm
content: Quote from: blueskull on June 17, 2016, 02:56:28 pmHiAt least for Intel, TDP really is an indicator of the size of the cooling solution required. A specific chip may (or may not) ever hit the magic 200W number. That said, yes, there is a lot of power going into those chips. It generally goes in on multiple rails to get around the current per pad / ball/ whatever issue.Bob

author: TiN
author_rank: Super Contributor
timestamp: June 17, 2016, 03:48:42 pm
content: Some folks like to overclock and overvolt their chips, so its more common than some might think. In those conditions power demand raises exponentially.I don't say that local multiphase buck is bad, what I say is design approach is still valid in both PSU in video and modern systems with local VREGs.On offtopic side, I measured power consumption of GPUs and CPUs in far end overclocking conditions (including nitrogen cooling and 60% higher voltage, yes). GPU like 780Ti or 980Ti easily talking ~1300-1500w RMS from +12V rail. CPUs like IvyBridge-E/Haswell-E/Broadwell-E can take about 500W. And TDP is not the maximum power chip can take, make no mistake.