Alright, just a little more of a status update:
The boards are working great! The 12V output works for running ~12 watts of strip LED, and the Omega can control it as expected. The 5V and 3.3V lines look great, even with some load, and the Omega's running without any issues. The whole thing is even pretty efficient - with a strip of LEDs, the Omega is putting out more heat than the converter.
There was a bit of a hiccup where I failed to recalculate a resistor value when I scaled the design from 3.3V output to 12V output. That was throwing the compensation loop out of whack, causing the 16 KHz ringing. After a bit of learning about feedback compensation and some circuit modeling, I calculated the correct value, and it's much happier now - no more audible whine, no more 16 KHz ripple in the 12V line. I'm now willing to declare that this design works!
I've even fixed the rest of my boards. Aside from the first one, which gave it's life for that resistor value fix, the other three work great.
I'm eager to go make something cool with this set up, but I know I got some people interested in a group buy. If I'm going to make that happen, I have a few questions for everyone:
- I've soldered the Omega down to my boards, but it should also be possible to put 2mm headers under them. Digikey is currently out of stock of the headers that are known to work, but I have some alternatives coming in a few days. The headers are only a few bucks, and only add ~4mmm of height. How many people would prefer to solder their Omega's down permanently?
- There's always going to be some ripple in the 12V line when it's under full 15W load - how much ripple is acceptable to you? I'm aiming for <150 mV, but I'm going to have to add a capacitor to get that. Am I the only one who cares? I might just leave an unpopulated pad for people to add a capacitor if they need it.
- We could save a few bucks if we decided
- I have the 12V output header controlled by a MOSFET, controlled by a GPIO. That GPIO, however, floats on startup, causing the 12V output header to be unpredictable. I want to add a resistor to hold it either high or low during power-up. So, 12V on by default, or off?
- If I run a group buy of these, how many are people interested in? They get cheaper the more that I order at once. $100 for 1, $78 for 4, $65@10, $60@40, $45@100 (approximate)... What kind of price range would people be interested in? How many?
P.S.: If anyone who works for Onion is reading, and wants to order and sell these so that I don't have to, that would be great! I'd love for my design to be the official PoE dock, and I wouldn't mind avoiding the trouble of running a group buy.