On 4/28/14, 11:33 AM, "Britton Kerin" <britton.ke...@gmail.com> wrote:
>On Mon, Apr 28, 2014 at 3:34 AM, Timbo <tim...@gmail.com> 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. Thinking about this, perhaps this is just simple pickup from your oscilloscope probe. This happens if you have a long ground wire on your probe. Connect the tip of the probe to your ground wire and move your probe over your power supply. If you still see the 500KHz ³fuzz², then you need to use a shorter ground wire. Regards, John > >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 beagleboard+unsubscr...@googlegroups.com. >For more options, visit https://groups.google.com/d/optout. -- 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 beagleboard+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
