One of the nice things about this whole concept is that -by coincidence- there is no need to mess with a power supply / regulator circuitry for the PXIe instrument.
In general a module needs a +12V and a +3.3V rail and a +5V with negligible current draw. In case of the PXIe-5644R the spec sheet says the following:
+3.3V..............4.9A (5.3A max)
+12V................3.3A (4.2A max)
Luckily the SATA power lines from the ATX power supply contain all three. I couldn't find what's the story behind most storage drives only using +5V and +12V to the extent that adapters from the old 5pin power connector are very common. I wonder if I am just not aware of disks using 3.3V or it was for a future use case in the standard that never become reality.
I put 3x SATA power inputs on the PCB, but only populated 2, for a maximum of 9A input per power rail over the connector contacts.
(As a side note it is fortunate that 2 connectors is enough, because I spaced them too close on the board, not taking into account the protruding part of the cable connector. Since 2 is sufficient, I just left the middle one unpopulated.)
The PXIe module has its own power conditioning and voltage regulation stage, but I still felt like I had to do something to compensate for the fact that the power is not delivered directly from a low impedance trace on the backplane, but through ~2 feet of wire, from a commercial psu. As a wholeheartedly half-a$$ed solution I put a 100uF tantalum polymer cap on each input voltage rail. I read something somewhere...
Since I didn't want to connect any disks to the same SATA power lines, I decided to make new point to point cables for them
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