On Mon, Apr 28, 2014 at 3:34 AM, Timbo <[email protected]> wrote: > Either there is a bad connection somewhere between the barrel jack and the > header pins (unlikely), or one of the power supplies is causing the problem. > I would check the resistance between the jack contacts and the corresponding > header pins, and then try powering via the headers with the known-good > supply. If that's ok, then (with the load connected) look for sag and > ripple on the other supply.
Well, its the supply. In some hideous way that I can't figure out how to measure. It works fine going straight from a wall wart to the header. The on-board 12V to 5V supply *looks* fine, it shows up a totally clean 5V on the scope, no noise that I can measure. There's 220 uF of output filter. But somehow 500 kHz triangular fuzz is showing up on the bone IO pin -- exactly the switching frequency of the step-down switcher. Its a design from TI switcher-pro. It also agrees almost completely with the reference design in Fig. 11 of the attached spec sheet. I feel sorta stupid to be using a design I don't completely understand, but I'd like to at least be able to measure where the problem originates. Any hints? Thanks, Britton -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
