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I'm making a device that will require two PCBs. One will be smaller, and pretty much just be the sensor that I'm testing. Almost like an evaluation board. This smaller PCB will be connected or inserted to a larger PCB which has all of the other components (some signal processing, biasing, a little microcontroller for data acquisition, etc).

The problem is that the sensor requires 4 different DC power supplies. Can I put power planes on both the smaller and larger PCBs, and connect them with a cable? The actual data coming in and off the sensor will use some high-density PCB-PCB connector, maybe an SO-DIMM architecture like this:

SO-DIMM RAM

I feel like I shouldn't use these connections for power lines though. The sensor is fairly power hungry, so I'd have to send a lot of current through those tiny pins, which seems like it wouldn't be the best idea. So as I see it, I've got 3 options:

  1. Put the voltage regulators on the larger PCB, and connect them to the smaller PCB through shielded coax cables.

  2. Put identical voltage regulators on the smaller and larger PCBs, and connect just a single power and ground line between them (I'm thinking this one isn't the best).

  3. Put voltage regulators on the smaller PCB, and connect them to the larger PCB through shielded coax cables.

Ideally, I'd want to use power and ground planes on both of the PCBs, to help with noise and losses over traces. But I have a feeling like I'm missing something important. Any advice would be welcome.

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  • \$\begingroup\$ Pick a connector type and analyze it's datasheet. The datasheet will tell you what current each pin can carry. Then use multiple pins to exceed this by 20% for a little margin (more if operating at temperature extremes, etc.) \$\endgroup\$ – rdtsc 2 days ago
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    \$\begingroup\$ "fairly power hungry" - surely you must know how power hungry. More than 16 GB of fast DDR3 SO-DIMM RAM (several watts)? \$\endgroup\$ – pipe 2 days ago
  • \$\begingroup\$ Seriously consider putting all the needed regulators on the smaller PCB, any cables will just add noise and other problems. You might also tell us how long the cables are! \$\endgroup\$ – Gil yesterday
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The pins on a so-dimm connect can handle 0.5 Amps to 0.75 Amps per pin. A pin on a PCI connector can handle 1.1 Amps. They are not as weak as you would expect. Use multiple pins if you need more current. Yes you could also use a local power regulator and higher voltage lower current through the pins, or a combination of both techniques.

Typically power input to a daughter card/carrier setup like this is the power comes into the carrier and passes through the daughter card connecter. Extra cables is only used on retroactive designs (think PCI E supplemental power connection) when the needs exceed the spec.

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it's a good practice to separate power and signal PCBs, separate high voltage used to power the sensor on the larger PCB and use some good connectors that can support high current (I used XT-60 and is pretty good, you can also use fork terminals). keep on the good work!

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