I have a circuit with two supplies, a 19 V supply for stepper motors, and a 5 V supply for driving the ATMEGA644, 3 stepper motor driver daughter boards, a Bluetooth LE daughter board, and two WS2812B RGB LEDs.
With two supplies everything worked, but I really wanted to get it down to just one supply. So I did another version of the board using just the 19 V supply and a VX78-500 switching regulator. I used their recommended input and output caps (but not the low noise version that include some extra inductors).
I have a 100 μF electrolytic on the 5 V rail. I'm not 100% sure if that's a good idea, but it's well below the max. capacitive load for the VX78-500 which is 680 μF and I thought it might help with noise.
I also have three 100 μF electrolytic on the 19 V line next to the stepper driver boards for the same reason.
When I first turned things on I noticed the WS2812b'd flashed slightly but everything was fine. That didn't happen on the two-supply version of the board. However, on maybe the 3rd or 4th time I turned it on the Bluetooth LE daughter board died, which is kind of surprising because it's got its own on-board 3.3 V LDO regulator.
I don't know that much about supply best practices/inrush current, etc. I knew my new setup would be noisier using a switching supply/being down stream from the same supply as the steppers. Any ideas what is going on? That flashing makes me think there's a bad spike happening at switch on time. It seems weird that the ATmega644 is still ticking but the BTLE daughter board died. How do I trouble shoot this?
Are those 100 μF caps just a bad idea in general? Does my circuit need some other form of protection?
Those daughter boards are $19 so I don't want to blow out too many of them in a search for the solution. Here is a pic of the PCB. I'm sure I'm just making some noob mistake, but I'd really like this one-supply version to work.
Ignore where that says 12 V, it's really 19 V. blush
Here are the two sheets of the schematic as well: