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Author Topic: Comparison of ALL Spartan6 boards: voltage regulator max current & efficiency  (Read 4353 times)
mrb
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June 13, 2012, 04:36:41 AM
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I compiled a table comparing the voltage converters supplying VCCINT to the Spartan-6 LX150, across all board manufacturers. The table below lists the maximum current that can be provided to each FPGA, as well as the efficiency of the converter at 8A (for 12V input, and 1.2V output):

ngzhang's ICARUS15A or 20A(*) per FPGATexas Instrument TPS40192 or TPS40193unknown efficiency
Enterpoint Cairnsmore112A per FPGAMicrel MIC2695087% efficient (from datasheet)
btcfpga ModMiner10A or 13.3A(**) per FPGADelta D12F20084% efficient (from datasheet)
fizzisist's X650010A per FPGAMurata OKR-T/10-W12-C83% efficient (from datasheet)
Ztex 1.15x/1.15y8A per FPGAAlpha and Omega AOZ1025D87% efficient (measured; datasheet says 75%)

(*) Some batches of ICARUS boards use the TPS40192 (rated 15A), others use the TPS40193 (rated 20A).
(**) The nice thing about the ModMiner is that you can decide to plug only 3 FPGAs in the mainboard, to give 13.3A to each FPGA, as they share a common 40A-rated voltage regulator.

eldentyrell: can you comment on how much current does your TML bitstream pull?
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Dexter770221
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June 13, 2012, 10:08:13 AM
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If chip is designed to deliver 20A it doesn't mean that whole DC/DC converter will. Many depends on coil, both efficiency and max current. ngzhang says that is 12A continous current for Icarus.
Micrel at 1.2V and 12A (12Vin) output have 83.5% efficiency. 87% is max at 3A output current.

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June 13, 2012, 10:11:42 AM
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Very useful information. Thanks!
mrb
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June 13, 2012, 10:15:56 AM
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Micrel at 1.2V and 12A (12Vin) output have 83.5% efficiency. 87% is max at 3A output current.

I quoted efficiency when outputting 8A, for all converters, regardless of their max output current, so that we can compare them all fairly.
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June 13, 2012, 10:57:32 AM
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Micrel at 1.2V and 12A (12Vin) output have 83.5% efficiency. 87% is max at 3A output current.

I quoted efficiency when outputting 8A, for all converters, regardless of their max output current, so that we can compare them all fairly.

Efficiency values are nearly useless without real world measurements on the FPGA boards itself. Values from data sheet are marketing. Maybe it makes sense for DC/DC module as ModMiner uses but not for self layouted with external low side FET (high side FET is integrated) and coil as ZTEX uses. Let's concentrate on Mhs/W values, as long as all available bitstreams are around 200MHs per FPGA its is good comparable. In my eyes Features as "Layout improvement for FPGA cooling" are more important until there are cheap FPGAs with metal head-spreader available. 12A @1.2V are challenging for the lousy LX150 package for long time.

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June 13, 2012, 11:06:22 AM
 #6

You mean FET?

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June 13, 2012, 11:08:09 AM
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You mean FET?
Your right, FED is more responsible for the fiat money Smiley.
mrb
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June 13, 2012, 11:12:23 AM
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Efficiency values are nearly useless without real world measurements on the FPGA boards itself. Values from data sheet are marketing. Maybe it makes sense for DC/DC module as ModMiner uses but not for self layouted with external low side FED (high side FED is integrated) and coil as ZTEX uses. Let's concentrate on Mhs/W values, as long as all available bitstreams are around 200MHs per FPGA its is good comparable.

Ok. This is what I was told by Stefan too. A lot depend on the external layout and components. So the efficiency numbers I quoted would make sense only for the ModMiner and X6500 as they both use pre-made modules.
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June 13, 2012, 11:57:14 AM
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Efficiency values are nearly useless without real world measurements on the FPGA boards itself. Values from data sheet are marketing. Maybe it makes sense for DC/DC module as ModMiner uses but not for self layouted with external low side FED (high side FED is integrated) and coil as ZTEX uses. Let's concentrate on Mhs/W values, as long as all available bitstreams are around 200MHs per FPGA its is good comparable.

Ok. This is what I was told by Stefan too. A lot depend on the external layout and components. So the efficiency numbers I quoted would make sense only for the ModMiner and X6500 as they both use pre-made modules.
For that micrel also should be good. There are integrated FETs and if cainsmore engeneers take good care choosing coil, efficiency shouldn't be worse than specified.

Under development Modular UPGRADEABLE Miner (MUM). Looking for investors.
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June 13, 2012, 12:12:58 PM
 #10

Ztex 1.15x/1.15y8A per FPGAAlpha and Omega AOZ1025D75% efficient

No idea where the 75% come from. According to my measurements on a 1.15x board (w/o fan, current at 3.3V counted as inefficiency) the efficiency is about 87%. (6.7A @ 1.23V vs. 9.4W at 12V).



mrb
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June 13, 2012, 05:29:25 PM
 #11

No idea where the 75% come from. According to my measurements on a 1.15x board (w/o fan, current at 3.3V counted as inefficiency) the efficiency is about 87%. (6.7A @ 1.23V vs. 9.4W at 12V).

The 75% comes from an estimation of reading the efficiency graphs on page 6 of Alpha and Omega AOZ1025D.
Anyway I updated the post. Thanks for measuring efficiency!
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June 14, 2012, 08:41:21 AM
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No idea where the 75% come from. According to my measurements on a 1.15x board (w/o fan, current at 3.3V counted as inefficiency) the efficiency is about 87%. (6.7A @ 1.23V vs. 9.4W at 12V).

The 75% comes from an estimation of reading the efficiency graphs on page 6 of Alpha and Omega AOZ1025D.
Anyway I updated the post. Thanks for measuring efficiency!

The data sheet says that this is the efficiency with an AO4722 external MOSFET. But I do not use this thing.

At 12V input voltage the efficiency of the AOZ1025DI mainly depends on that MOSFET and the coil.

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