Well, I got my SP20 a little later than most and didn't get to the review as soon as I'd like, so this will be a bit different than most.
Most others have gone over the basic unboxing and review of the web interface, so I won't touch on that here. Instead, I'll go over a couple parts of the hashing board for people who might not know what all the parts are.
Disassembly
Holding each heatsink on is a glob of extremely tough glue. They really don't want these things coming off. If you do get it off, you can remove the heatsink.
Under the heatsink is a copper shim, with some thermal grease at the interface. The shim had some strange imperfections though.
As you can see, there's a couple marks on the shim, right where it touches the die. Not really ideal, but it didn't seem to really make a big difference. Underneigth, well..
That's a LOT of thermal paste. Thankfully they use an extremely high flow compound, so it all just squeezes out the sides. Clean it off, and you get a much better look at the die.
That's much better. As you can see, this die was packaged in week 44, so end-Oct or the start of November. They don't have a huge lag between getting chips in and sending out products. You can also see SP is using an 8 layer board from the layer marker at the top of the image.
VRM Show and TellNow that we've got the board nicely take apart, let's see what is going on for each ASIC. First the top of the board.
There's a few supporting blocks in frame here. First, in green there is a DC/DC convertor that provides one of the minor voltage rails.
The blue squares are a pair of LM75 temperature sensors. These have a digital I2C interface, and they run to an I2C switch between the sensors and the minor voltage rail.
Up top in pink you have some caps on the 12V rail right near the output devices.
The center is dominated by the VRM controllers. SPTech went with two TPS40425 analog converters, in a master/slave relationship to provide 4 phases to the ASIC.
These are driverless convertors, they just provide the brains and don't drive any mosfets directly. To see the main outputs, we need to look at the other side.
Starting at the bottom, in red you can see an input inductor that filters the incoming 12V from the PSU. In pink you can see more caps on that filtered 12V rail. While the 12V rail doesn't have nearly current flow as the 0.7V output, the change in voltage wrt time (dv/dt) is extremely quick, so it's good to see lots of decoupling there.
Next in yellow you can see the main output devices, TI's CSD95372. These 60A devices are quite new parts, with some very nice looking specs. They provide the main switching that converts the 12V rail into pulses of 12V that will be filtered later.
Before the output inductors, there's two more components in blue that for a zobel network. The zobel helps to reduce some high frequency ringing on the switching waveform. It's a bit of a safety, you don't want too much ringing, but the zobel does dissipate energy so it can reduce efficiency a bit.
Next up is the main inductors. These guys are the main filtering elements, and are what change the pulsed 12V waveform that comes out of the mosfets into a very wavey 0.7V. To get the output nice and smooth we still need more filtering though.
At the top of the image in light blue you have the main output capacitors. There guys get charged up while the inductors are flowing current, and discharge it to the ASIC while the inductors are off. They also provide another often overlooked but very important protection. Because current through an inductor doesn't change instantly, if the load switches off suddenly (like the ASIC is no longer hashing) the high current will keep flowing and the voltage can spike. Often the minimum capacitance you need isn't set by what you need to keep ripple low, it's chosen to keep the maximum voltage low enough to prevent damage in the case that the ASIC suddenly stops hashing.
Lastly at the top of the image you can see the bottom side of the ASIC, with a bunch more small value decoupling caps as close to the chip as possible.
Anyway, I hope this has been a bit informative. I'm trying to fight off a killer head cold and probably have minutes left before the NyQuil finishes kicking in, so I'll check back in tomorrow to see if there's any questions.
