I have an application where we are supplied 24VDC but need to drop that down to 5V for some of our control circuitry. For DFM reasons, we are limited to buck converters that can only safely supply 3A; we may need more than that at certain points in time. Each board has a Molex connector going back to our main controller. The Molex connector will deliver 24VDC, 5VDC, GND (2), and I2C(2). The controller board itself may take up to 3A at any moment in time, but we still need to deliver 5V to each of the slave boards.

We are in the design phase and so we don't have any schematics yet. Right now, we're thinking we'll use the TPS54331DR on each individual board (master and slaves).

Is it safe enough to diode-OR these with a Schottky and put a regulator on each board with 5V "shared" between all of them? Is there a better way to parallel these buck converters given that we're locked into a handful of sub-par converters for this project?

Is this even necessary to try to share the 5V amongst boards? Would we be better off omitting the 5V line from our Molex connector?

Any advice is appreciated. I will answer questions as quickly as I can. Thanks!

  • \$\begingroup\$ Are there any constraints (cost, or redundancy/reliability) that would stop you putting a 24/5V buck on each board? If there's any distance between them, separate supplies will guarantee the 5V rail on each board, while inter-board wiring may not. \$\endgroup\$ – Brian Drummond Dec 21 '20 at 12:49
  • \$\begingroup\$ Nope. We can put them on each board. I just had a feeling that we would need to tie all the 5V lines together so the I2C communication doesn't end up at weird voltages, but I have no basis for that claim. \$\endgroup\$ – Ryan Norton Dec 21 '20 at 15:13
  • \$\begingroup\$ Tthat's where my desire to just have a shared 5V line came from. Have a regulator on each board, and diode-OR them all to a main 5V line. This may be overkill and I've thought my way into a problem. \$\endgroup\$ – Ryan Norton Dec 21 '20 at 15:13

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